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Trente ans de lutte contre l’onchocercose en Afrique de l’Ouest. Traitements larvicides et protection de l’environnement

Laurent Yaméogo
Christian Levêque
Jean-Marc Hougard

Joint US-AID/OCCGE/WHO technical-meeting on the feasibility of onchocerciasis control


Texte intégral

1A technical meeting on the feasibility of onchocerçiasis control was convened in Tunis from 1 to 8 July 1968 under the sponsorship of the United States Agency for International Development (US-AID), the "Organisation de Coordination et de Coopération pour la Lutte contre les Grandes Endémies" (OCCGE) and the World Health Organization (WHO). Professor P. G. Janssens was elected Chairman, Dr E. Akwei Vice-Chairman, ànd Dr B. O. L. Duke and Dr M. M. Ovazza were elected Rapporteurs. The meeting was opened by Mr H. Khefacha, Secretary of State for Public Health Affairs of the Government of the Tunisian Republic.

2The twenty-seven experts gathered represented various disciplines involved in the control of onchocerciasis: public health, tropical hygiene, parasitology, epidemiology, entomology, ophthalmology, medical training, economics, sociology and medical geography. The meeting was serviced by a joint US-AID/OCCGE/WHO secretariat. It was attended by a representative of the International Bank for Reconstruction and Development (IBRD) and by an observer from the "Office de la Recherche Scientifique et Technique Outre-Mer" (ORSTOM) (see list of participants).

  • 1 Wld Hlth Org. techn. Rep. Ser., 1966, 335.

3In 1965 the World Health Organization convened an Expert Committee on Onchocerciasis to provide guidance on the methods of approach to onchocerciasis control best adapted to existing epidemiological conditions.1 In the three years that have since elapsed, although some advances were made in several fields of research, it was felt that knowledge had progressed but slowly, particularly on the actual geographical distribution of the disease and its pathogenicity.

4Successful control has been achieved in the last twelve years in some geographically well defined foci, notably in Kenya where the eradication of Simulium neavei was completed in 1956 except for a very small focus on the Uganda border. On account of these encouraging results, a number of new control projects have been started in the last five years. Good results have been obtained but at the price of many difficulties, both technical and financial. It was therefore felt that the time had come to undertake a critical review of the experience gathered in the projects recently carried out.

5In addition to the technical and financial difficulties encountered, operations in progress have raised another set of problems. Owing to the Limited extent of the areas, under control, these areas, even when successfully treated, remain under the threat of an early reinvasion by Simulium flies from adjacent areas that have not been protected. This raises the problem of a concerted action between neighbouring countrïes.

6In view ofthe above, the present meeting was called to advise on the best strategy to be adopted in the present epidemiological circumstances, the conditions under which control should be attempted, the methods to be used, including the most modern techniques, and the requirements (staff, equipment, funds, inter-country co-ordination) to be met.

7Onchocerciasis is rife in many countries. Obviously, its control cannot be attempted everywhere at the same time. The meeting was therefore asked to point out the areas where the onchocerciasis problem is greatest and where an expanded project could be carried out with the maximum chances of success.

8In recent years public health administrators and field workers have drawn attention to the devastating economic repercussions of onchocerciasis. Some of the most fertile river valleys in tropical Africa have remained deserted and uncultivated or are progressively abandoned, and it seems that the occurrence of the disease and of the Simulium vectors is a major deterrent to the reclamation of these valleys. Furthermore, the presence of the Simulium vectors, which are dreaded both for the terrible nuisance they cause and as the vectors of onchocerciasis, has also hampered the implementation of large economic development schemes in certain areas. Onchocerciasis has now acquired the status of an "economic" disease and, as such, is of interest to national authorities responsible for economic development planning as well as to international and national organizations providing technical and financial assistance to economic projects planned or carried out in developing countries.

9A revised strategy of onchocerciasis control, enlarged to include whole river basins, will obviously require financial efforts which must be warranted by the economic benefits they are expected to provide. In order to facilitate this assessment, the experts were asked to define the requirements for a large-scale onchocerciasis control project applicable to the recommended initial project area.

10The present report is an account of the views expressed and recommendations made on these various questions.


11Onchocerciasis may be regarded as being in a state of dynamic equilibrium. In the present section the current situation is first reviewed and an attempt is made to foresee some of the changes that may take place in the future.

1.1 Magnitude of the current problem

1.1.1 General situation

12Onchocerciasis is a parasitic disease widely distributed in tropical Africa and the Americas. In Africa, the disease is known to occur south of the Sahara in a wide belt stretching from west to east. The northernmost boundary of this zone coincides roughly with latitude 15°N and runs from Senegal to Ethiopia. South of the equator the endemic area extends down to Angola in the west and to Tanzania in the east. Apart from highly endemic areas in the south of the Sudan Republic, small foci have also been reported in the north of that country as well as in Yemen. In the Americas, important foci exist in Mexico, Guatemala and Venezuela. A small focus has recently been discovered in Colombia.

13It is estimated that approximately 20 million people in the world are infected with Onchocerca volvulus, the majority of whom live in Africa. However, this figure is probably an underestimate and does not fully reflect the importance of the disease. To give a more concrete example, in Upper Volta alone, it is estimated that, out of a population of 4.5 million, 400 000 have onchocerciasis. Of these 400 000, 40 000, or one in ten, suffer from severe eye lesions and many of these are actually blind.

  • 2 A detailed description of the onchocerciasis situation country by country is given in a separate d (...)

14A summary of the global distribution of onchocerciasis as known today is presented in Map 1 (Africa) and Map 2 (the Americas). The endemic onchocerciasis areas marked on these maps represent, however, a conservative estimate. The geographical distribution of the disease still requires more precise determination. In many instances the blank spaces in the tropical belt of the African map indicate gaps in our knowledge rather than absence of onchocerciasis. The area in which the vector exists without the disease itself being found is usually more extensive than the endemic area marked on the maps.2

15The greatest impact of onchocerciasis occurs, without doubt, in West Africa between the 8th and 12th northern parallels of latitude, where the prevalence of blindness and other clinical manifestations are extremely high.

1.1.2 Situation in West Africa3

  • 3 For geographers, the division between West and Central Africa is approximately the valley of the C (...)

16All the States of West Africa are affected by onchocerciasis: Dahomey, Gambia, Ghana, Guinea, Ivory Coast, Liberia, Mali, Mauritania, Niger, Nigeria, Portuguese Guinea, Senegal, Sierra Leone, Togo and Upper Volta. Moreover, as is generally agreed, it is in West Africa that the most serious foci are located. Nevertheless, in this part of Africa gradations in the severity of the disease may be observed. Thus it is possible to distinguish two distinct types of transmission:

(1) The forest type of onchocerciasis

17In the forest zones, the foci are extensive and continuous with adjacent foci. However, although individuel infections may be very intense, serious disorders such as blindness are relatively uncommon. It should, however, be noted that the nuisance caused by the vector, which in certain foci and at certain seasons literally swarms (4 000 bites per man per day), may constitute a serious problem for the use of riparian lands by man. This forest type is encountered in the Southern part of West Africa stretching from Cameroon to Guinea.

(2) The savanna type of onchocerciasis

18Here the foci are restricted to communities either living in close contact with the vector species, or brought into frequent contact with them through the normal activities of their daily life. In these areas, the morbidity rate falls rapidly as one moves away from the rivers.

19With the second type, in contrast to the first, the individual parasite load is very high. The clinical manifestations are usually severe, with a high rate of blindness.

20Moreover, a particular feature of certain parts of the savanna zone is that there has been an actual abandonment of villages in the river valleys. This can be considered as the most severe. socio-economic impact produced by onchocerciasis,. For ecological reasons specific to the vector, this all too frequent depopulation effect occurs only in the savanna areas. It is encountered in the northern and central regions of Nigeria, Dahomey, Togo, Ghana, the Ivory Coast and Guinea, and in the southern and central regions of Niger, Upper Volta, Mali and Senegal.

1.2 Factors likely to alter the distribution of the disease

21The distribution of onchocerciasis is not static. From several parts of Africa evidence exists that the situation has been aggravated by extending and improving agricultural practices through irrigation and open water storage. In many parts of Africa the increasing numbers of dams and causeways, mainly for irrigation purposes, have caused a spread of Simulium vectors, thus extending the area of potential risk of onchocerciasis transmission.

22On the other hand, the building of dams and the consequent transformation into lakes of stretches of rivers situated above the dams may result, in the elimination of many breeding sites upstream. However, in some cases due to local topographical conditions, new breeding sites appear on tributaries of such lakes.

23Large-scale movements of population in connexion with development projects may result in the spread of onchocerciasis to new areas.

1.3 Public health importance

24The most serious consequences of onchocerciasis are impaired vision and blindness. Thus, like trachoma, the disease affects human beings' most valuable and precious faculty, eyesight. The loss of vision not only reduces the working capacity of the population in the endemic areas but has far-reaching repercussions.

  • 4 Greenslade, C. (1956) Incidence and causes of blindness, London, British Empire Society for the Bl (...)

25The relative proportion of ocular manifestations is much higher in onchocerciasis foci than in any other region. Published figures4 collected by the British Empire Society for the Blind indicate that the number of cases of blindness per 100 000 inhabitants is 250 in Europe, 500 to 1000 where there is endemic trachoma, and 1500 or more in countries where hyperendemic onchocerciasis occurs in some areas (i.e. 1.5%).

26In some villages of Upper Volta, Ghana and Nigeria the blindness rate reaches about 10%. This corresponds to up to 30 per cent. in the working population and in these areas depopulation is occurring. By comparison, villages free from onchocerciasis but lying in the same geographical region show blindness rates of 0.5 to 1 per cent.

27The actual situation of blindness in an onchocerciasis endemic area of Northern Ghana, as shown in Map 3, demonstrates the gravity of the problem, especially if one considers that blindness in such hyperendemic areas is often already established in the 20-30 year-old age group.

28Apart from total blindness of onchocercal origin, various degrees of impairment of vision, which decrease occupational ability to an extent difficult to estimate, must also be taken into account. Even simple conjunctivitis, because of its lasting nature, is a serious handicap to those affected.

29Other manifestations of the disease involve primarily the skin and lymphatic system and in their most serious forms can also cause great suffering to the affected individuals. In extreme cases of pruritus and lymphadenopathy, people may be rendered quite incapable of leading a normal life or maintaining normal social relationships.


30Control of onchocerciasis may be achieved either by measures designed to control the vector Simulium population or by measures designed to eliminate the microfilarial reservoir from the human population. The latter method is theoretically possible since it is unlikely that any significant animal reservoir exists for Onchocerca volvulus, but it is at present impractical to put it into effect as none of the drugs available is really suitable for use in mass control campaigns. It is greatly to be hoped that further research will be undertaken to find new non-toxic drugs which are active against O. volvulus and which may be used in combination with Simulium control operations to achieve control of onchocerciasis, but for the time being vector control remains the only practical means of reducing transmission on a large scale.

31Although elimination of the vector may not be necessary in order to stop the reproductive cycle of the parasite, at the present stage of knowledge the maximum degree of control of the vector density should be aimed at. In order to achieve interruption of transmission whenever this seems possible, vector control could be supplemented by measures aimed at reducing the microfilarial reservoir in the human population.

  • 5 Wld Hlth Org. techn. Rep. Ser., 1966, 335, pp. 51-78
  • 6 Wld Hlth Org. techn. Rep. Ser., 1966, 335, pp. 15-24, 28-45

32The following review refers to new trends and developments that have occurred in control and assessment methods since the Informal Meeting of WHO Advisers on Entomological Needs in Onchocerciasis Control (July 1964)5 and the meeting of the WHO Expert Committee on Onchocerciasis (June-July 1965).6

2.1 Control methods

2.1.1 Vector control Grouhd application of larvicides

33The objective of larviciding is the elimination of the immature stages of S. damnosum from the rivers of the area under control.

Choice of insecticides

34DDT has been the insecticide of choice for the past 20 years, and emulsifiable concentrates appear to be the most suitable formulation. Wettable powders, although attractive because of cheapness, have a shorter "carry" than emulsions. Concentration of DDT may vary from 0.01 ppm (p,p'-isonier) to 1.0 ppm per 30 minutes in an inverse relationship to the size of the river. Discharge, velocity and nature of the river also influence the concentration required. Dieldrin has given good control at concentrations as low as 0.0003 ppm/30 minutes but is not considered suitable because of its high toxicity to man and other vertebrates.

35Because of the possibility that Simulium larvae may develop resistance to DDT, and because of DDT's persistence and accumulation to texic levels in non-target organisms, field trials have been carried out with a number of other insecticides. Of those tested, methoxychlor, Abate, Dursban, sumithion and carbamyl appear to be the most promising. Methoxychlor is as effective as DDT in killing blackfly larvae when applied in the same time/concentration conditions. It is non-persistent and will not accumulate to toxic levels in fish and other aquatic organisms.

Method of application

36Simple methods are recommended, the usual method being to let the insecticide drop into the water through a hole in the bottom of a tin.

37The recommendations as outlined in the report of the WHO Expert Committee on Onchocerciasis (reproduced in Annex 3, section 1) are accepted with the following modifications

"(6) Dosage be at a rate not exceeding 1.0 ppm and not less than 0.01 ppm maintained over 30 minutes. Discharge can be calculated by measurements of width, average depth and maximum speed of flow in small rivers but in large rivers hydrological data are required."

"(11) The concentration of the insecticide should be calculated on the basis of a theoretical dosing time of 30 minutes. However, the actual dosing time may be reduced to as little as one minute or continued for more than an hour, depending on local circumstances, but the total quantity applied remains the same." Aerial larviciding

38In large-scale programmes covering a very large area rapid, complete, and effective application of insecticide is of prime importance. These criteria are met with by aerial application techniques.

39Aerial larviciding for blackfly control has been widely used in heavily forested regions of the United States and Canada with good results for many years. Modern pressure spray equipment was utilized. In Africa, continued aerial spraying was practiced in the Kinshasa area and resulted in the disappearance of Simuliidae for several years. It can be applied in areas otherwise inaccessible or which require extensive road construction. Large areas can be treated quickly allowing more efficient Use of the professional staff. Lower dosages can be resorted to, probably because of better dispersion of the insecticide in the stream, which increases the efficiency of the technique and also reduces the possibility of direct or indirect injury to fish. The dosage is to a great extent automatically regulated by the stream width.

  • 7 Solvent: Heavy aromatic naptha with fuel oil added to give a specific gravity of about 0.995 and w (...)

40Effective dosages in North America have been 15-20% oil solutions of DDT7 or methoxychlor applied at the rate of one gallon per flight mile in swaths 1/4 mile apart using a wide variety of aircraft with modern spray equipment (e.g. with Piper standard systems, 3-D4 nozzles, 40 psi, flying at 120 mph at tree-top heights). This form of aerial application may be of special value during seasons when rivers are in spate and inaccessible or, conversely, when very low and divided into a large number of separate breeding areas.

41Stream treatment by "bombing" from aircraft with cartons containing insecticide may be useful under special circumstances. However, aircraft equipped with conventional insecticide spraying apparatus can do this more accurately and efficiently, and with a more even dispersion of the insecticide, and is therefore to be preferred. Aerial application of adulticides

  • 8 Wld Hlth Org. techn. Rep. Ser., 1966, 335, 31

42As noted in the WHO Expert Committee Report,8 DDT aerial spray applied at the rate of 0.2 1b per acre (0.224 kg/hectare) for blackfly control in North America significantly reduces adult fly populations for periods up to ten days. It is a control measure of short duration which quickly reduces adult populations and therefore has some possible use as a supplement to the basic control measure, larviciding.

43In savanna regions of Africa it may be useful if applied along river margins where the adult blackflies emerge, rest and return to oviposit. It may also be advantageous to form a protection barrier on the periphery of other zones controlled by larviciding. Ground application of adulticides

44Truck-mounted thermal aerosols are widely used in North America for control of adult blackflies in densely populated areas where there are many access roads. They provide temporary relief from annoyance by killing the flies the insecticide comes in contact with, in very limited areas. 5-8% DDT in oil solutions (fuel oil or heavy aromatic naptha) are commonly used. It is an expensive, non-persistent method of control, probably of little use in onchocerciasis control programmes. Environmental control methods

45In view of the strict localization of the larval and pupal forms in water-courses or sections of water-courses with adequate speeds of flow, it has been demonstrated that elimination of the indispensable ecological factors renders impossible the development of the vector species. To achieve this, one method is by damming to create reservoirs of sufficient size to eliminate any flow over considerable distances upstream of the dam. The building of these reservoirs will help in the strategy of campaigns by forming protection areas which will reduce the possibility of reinvasion of the controlled areas. Moreover, these lakes, in case of an unexpected interruption of the campaign, could limit the risks of infection in areas recently resettled by non-infected populations.

46Dam spillways and flood gauges should as far as possible be constructed in such a way as to prevent them forming suitable breeding places for Simulium.

2.1.2 Parasite control Nodulectomy

47Experience in Guatemala and Mexico has shown that the operation of nodulectomy can be carried out simply and effectively by organized mobile teams, provided they are well equipped and Haye acquired practical experience in this particular form of minor surgery. Regular nodulectomy campaigns have been carried out for the past 25 years, so that once every 6-12 months all palpable nodules are removed from the population attending. The clinics are popular, attendance is good, and the method is reported to be effective in controlling the high incidence of blindness and of "erisipela de la Costa". In Mexico and Guatemala denodulization has made it possible to reduce the incidence of onchocercal blindness from the 5 to 15% level which prevailed at the beginning of the campaign to the present level of 0.5 to 1%. However, the campaign appears to have brought about little significant reduction in the amount of transmission. Its clinical success in the Central American form of the disease is largely due to the frequency with which palpable nodules are found on the head, leading to early and heavy microfilarial invasion of the eye. Nodulectomy effectively reduces and controls this invasion.

48The inadequacy of nodulectomy is due to the presence of adult worms which lie deep in the tissues and are impalpable from the surface of the body. One has only to observe the large numbers of microfilariae present in patients who have no palpable nodules to be certain of the existence of these cryptic worms, and worms lying free in the tissues have been reported at operation. In addition, experimental work on chimpanzees has shown that the great majority of the worms in these animals lies deep in the tissues between the muscles and often near the bones and joints (especially around the capsule of the hip joint).

49As nodulectomy has not been successful, even in Central America, in reducing the microfilarial reservoir in man to a level at which transmission becomes ineffectual, the method can be ruled out as a practical measure to attain this end in Africa. Moreover, as nodules on the head are uncommon in Africa, a reduction in the incidence of blindness is unlikely to be achieved by this means and the operation has never given good results as a control measure. Chemetherapeutic methods

50The primary aim of a control project is to eliminate the serious eye lesions and other clinical manifestations of the disease. Chemotherapy may play a part in achieving this both by reducing the worm load of an individual to a level at which serious eye lesions no longer occur, and by reducing the microfilarial reservoir in the human population so that treated persons cease to be a source of infection to feeding Simulitdae and transmission is interrupted.

51While suppressive regimes directed against the microfilariae alone should not be disregarded, provided they can be maintained for the long period necessary before the adult worms die, it is obvious that chemotherapy directed against the adult worms themselves will have a much more prolonged and fundamental action in reducing microfilarial concentrations.

Mel W

52Until recently this arsenical preparation was thought to hold considerable promise as a macrofi-laricide for mass use by single-shot intramuscular injection. Regrettably, it has since been shown that in a significant proportion of patients fatal arsenical encephalopathies may follow its use, and there is considérable doubt as to the efficacy of the drug when used in single dose treatments even as high as 10 mg/kg. The use of Mel W in mass campaigns cannot at present be recommended.


53Suramin in adequate dosage (1.0 g weekly to a total of not more than 6.0 g) has proved effective as a macrofilaricide and has also a microfilaricidal action. Severe reactions, including deaths, have been reported when suramin is used (see Annex 3, section 2), and on ethical grounds the drug cannot at present be recommended for mass therapy purely as a means of reducing the reservoir of microfilariae in the human population in an attempt to break transmission. However, where transmission has been reduced by vector control, it may well be justified to treat those persons in a heavily infected population, in whom severe or blinding eye lesions may be anticipated from the effects of their existing load of parasites. Such treatment must be given under medical supervision.


54For all practical purposes diethylcarbamazine can be considered as acting against the microfilariae. In mass control schemes it could probably be used with great effect to reduce the microfilarial reservoir in the human population.

55Treatment consists in giving 50 mg diethylcarbamazine acid citrate once a week until the initial load of microfilariae has been eliminated. This process may take about six to eight weeks, during which time the patient undergoes a series of reactions to the death of microfilariae, declining in severity each week. Thereafter, the weekly dose can be taken with little or no inconvenience and may be continued, if necessary, throughout the life of the adult worms. The life-span of the microfilariae being some 24-30 months, the initial load of microfilariae probably represents about a 12-15 months' supply and, once this has been eliminated, the number reaching the skin each week from the adult worms will thus, in theory, be between l/50th and l/65th of the initial load. The death of this relatively small number each week under diethylcarbamazine can usually be brought about at the expense of an almost insignificant reaction in the patient.

56Reactions encountered during the early weeks of treatment may be controlled to some extent by simultaneous dosage with antihistamines. However, Mexican workers state that reactions are due to release of serotonin rather than histamine. They have acquired considerable experience of treating reactions with serotonin antagonist drugs. Blind coverage with steroids is not justified in a mass campaign on account of the risks involved with these preparations, but if severe eye reactions are encountered local steroid therapy may be needed.

57The population to be treated must be warned of the nature and severity of the reaction to be expected following the early doses. It should be explained that this is a result of killing the small worms in their skins, that it is dramatic evidence of the power of the medicine, and that it will be of short duration. Skilful propaganda on these lines may well succeed in overcoming resistance to co-operate.

58Such a suppressive regime has two great advantages. First, the microfilariae are killed as soon as they arrive in the skin and before they can invade the eye so that its use may serve to halt the progress of eye lesions. Secondly, the patient ceases to be a source of microfilariae for feeding Simulium and thus a reservoir of transmission. However, the method may be difficult to apply in practice and has never yet been tried on a large scale. If it is considered desirable to use it as an adjunct to a Simulium control programme, it would be wise to conduct a pilot scheme in the first instance in one or two villages (starting with those which are less heavily infected) so as to assess its practicability under field conditions.

2.2 Surveys and assessments

59Prior to instituting control measures, entomological and epidemiological base-line data should be obtained by means of carefully planned and conducted preliminary surveys. Thereafter, throughout the course of the control campaign, similar surveys should be conducted in order to evaluate the effectiveness of the measures instituted.

2.2.1 Entomological Surveys: Data to be obtained before, during and after treatment

60(a) Simulium larval survey: This survey should be carried out in all streams throughout the year in the preliminary phase and, during the attack phase in selected points while dosing and after treatment. Quantitative sampling is not practical at present.

61Careful mapping of all breeding sites is indispensable.

62(b) Simulium adult survey: Catching female S. damnosum on human bait should be carried out routinely by means of full-day collections made at 1 or 2-week intervals. Such catches must be made at sites inside and outside the treated area and along its margins. Counts should be continued for at least a full year before control is started. The unit is f/m/d (number of flies per man per day). The physiological age of the collected flies should be determined by dissection.

63(c) Survey of O. volvulus transmission: To obtain information on the level of transmission in any given area the number of O. volvulus infective larvae per fly and the number of infected and infective flies per man per year should be recorded. Evaluation of results

64(a) Larvae: All S. damnosum larvae should be eliminated by the first treatment and so counts should then be zero.

65(b) Pupae: The presence and age of pupae after treatment provide supplementary information on the effectiveness of larviciding. Pupae should disappear by the second cycle of treatment.

66If larvae are not eliminated in the first cycle of treatment, the dosage, or the distance between treatment points, may require adjustment. Should pupae continue to appear, the interval between treatment times should be shortened.

67(c) Adults: Adult dissections will provide information as follows:

  1. Persistence of nulliparous females after treatment indicates that some breeding sites may persist or immigration from untreated areas is occurring.
  2. If control of all breeding sites is complete, with the result that the local fly population has disappeared, an increasing proportion of nullipars indicates a selective migration of young females to the area.

68(d) O. volvulus transmission: During the campaign, in the absence of invasion from untreated areas, the infection rate will increase temporarily as the average age of surviving females increases.

69If there is an invasion of flies from outside the control area, the infection rate may decrease because of the lowering of the physiological age of the population.

70From these data, the number of infective larvae transmitted per man per year can be calculated at different points in the control area. The aim is to reduce transmission at least to levels no higher than those occurring in epidemiologically comparable areas where the disease is present but does not cause disability-in man. Susceptibility of vectors to insectide

71Decreased susceptibility of Simulium larvae to DDT has been reported in Japan and North America. The possible widespread development of resistance is a factor to be taken into consideration in any large-scale onchocerciasis programme in Africa.

72A procedure for testing larval resistance has been developed (WHO) and, in modified form, has been extensively used. It can give consistent and homogenous results when carefully used.

73Susceptibility levels should be routinely checked by discriminating concentrations with modified jar tests in the field and, when detected, followed by more detailed laboratory tests to determine dosage mortality relationships.

2.2.2 Morbidity Objectives

74The first task is to map the geographical distribution and evaluate the endemicity and severity of onchocerciasis within the country when accurate data are not yet available ("initial prevalence survey").

75The second task is to record the trend of the disease in relation to control. For this purpose a limited number of indicator areas will be selected ("detailed surveys"). Initial prevalence survey

  • 9 Wld Hlth Org. techn. Rep. Ser., 1966, 335, pp. 16-24.

76This survey should be undertaken to determine the extent of onchocerciasis in a statistically representative number of villages. A qualitative skin snip method as described in the WHO Expert Committee report9 (see Annex 3, section 3) should be employed, and visual acuity recorded. Detailed surveys of selected indicator areas

77Along each major river system, areas should be chosen to represent high, medium and low endemic zones (see Annex 3, section 4), care being taken to include communities with high, moderate and low incidence of blindness.

78The areas chosen should lie in close relation to the entomological assessment sites at which S. damnosum are to be captured (see section so that the effects of the scheme on the amount of transmission can be related to its effects on the disease in the human population.

79Wherever possible, the entire population of each indicator area should be examined and basic data recorded on each person using the Individual Onchocerciasis Record Card suggested by the WHO Expert Committee (see Annex 3, section 7).

80The first detailed survey must be conducted immediately before, or at the time, control commences. It should be repeated at 2-3 year intervals, using the same methods and if possible the same personnel.

  • 10 Wld Hlth Org. techn. Rep. Ser., 1966, 335, pp. 16-24.

81Although in general agreement with the Expert Committee report,10 the following points are believed to provide important comparative data for the assessment of the success of the campaign.

82(a) Two approaches might be used in the parasitological assessment of the campaign.

  1. Study of selected age groups, by comparing the incidence and intensity of infection in given age and sex groups. The findings should be particularly significant in children;
  2. Follow-up of the progress of the disease in individuals chosen from those examined at the initial survey (cohort study).

83As there is a time lag between the acquisition of infection and the appearance of microfilariae in the skin detectable by skin snip, it is important that as many cases as possible should be detected in the younger age groups since if they are missed and later show a positive skin snip, they might lead to the erroneous conclusion that infection has been acquired since the initial survey. As a supplementary investigation the Mazzotti test could be employed to identify early infections in the younger age groups. It was reported that this method has proved of greater value in mass surveys than anticipated (see Annex 3, section 5), provided the area is not heavily infected by other filarial diseases.

84(b) The most important ill effects of the disease are impaired vision and blindness An ophthalmologist, equipped with a mobile slit lamp, must be made available to survey the indicator areas in the control area. He should complete the ophthalmological sections of the Individual Onchocerciasis Record Cards, adding a record of fluffy stromal corneal opacities typical of onchocerciasis and of other causes of impaired vision and blindness.

85(c) The first survey in the indicator areas will provide data which give a base-line. Subsequent surveys carried out by the same methods will then be comparable.

86(d) In section, treatment is suggested for those persons considered to be under a continuing threat of blindness from their existing worm load. The evolution of the eye lesions in these treated patients should be compared with that in untreated patients also living in the control area.

2.3 Examples of success and failure of control schemes

87Although the Mayo Kebbi project in Chad could have been successful due to the area being partly isolated, its relative failure may be ascribed to:

  1. insufficient co-operation between the various units of the project;
  2. the lack of planning (too short preliminary surveys);
  3. incomplete assessment of results;
  4. indiscriminate use of sophisticated techniques without preliminary study of their applicability under local conditions.

88At Abuja, Northern Nigeria, where 100 miles (-160 km) of rivers in an area of 1200 square miles (3100 km2) have been treated annually during the first three months of the wet season since 1957, the S. damnosum biting density has been reduced by over 90% to usually less than one bite per man per hour. In spite of this reduction skin snip surveys show that, although there is an indication that the microfilaria density has been reduced, there is no doubt that transmission is still taking place. The fly density measurements in this scheme were based on weekly 15 minute catches at 43 sites within the controlled area. It is thought that full-day catches might have given a better estimate of the Simulium density, and also provided larger numbers of flies so that age and infectivity dissections would have had greater meaning.

89The Sikasso focus in Mali has been under treatment for several years and it has been possible, by adapting the treatment to local conditions, by keeping the zone under close surveillance, and by eliminating existing possibilities of reinfestation through the establishment of larvicide barriers, to obtain a considerable reduction in the density of the vector species. Except for one point in the downstream part of the zone where a very limited population of vector females (2% of the pre-campaign population) still persists, it can be considered at present that transmission has practically ceased throughout the zone, as shown by entomological and clinical assessments.

90Control of S. damnosum in the Victoria Nile in eastern Uganda was first instituted in 1952, when DDT was applied as a larvicide at a rate of 1 ppm/30 min for 10 weekly applications. Eradication was achieved, but reinfestation occurred in 1953. Subsequent treatments in 1956, 1961 and 1964 were necessary to maintain a fly-free state. The picture is one of intermittent eradication for periods of about four years. The source of reinfestation is not known.

91At this stage, when the control areas are exposed to reinfestation from outside, as in Abuja, Murchison Nile and Sikasso, the campaigns must be continued on a maintenance basis, otherwise the S. damnosum problem will quickly return.

2.4 Problems involved in onchocerciasis control

2.4.1 Problems related to vector control in large-scale projects11

  • 11 A review of "Research problems involved in vector control methods" is appended (Annex 1)

92With large-scale control the problems of transport, staff, and logistics, in general, will be multiplied many times. The problems of collecting data for evaluation will also be formidable. Methods that are satisfactory for small areas of 10 000 square miles (25 000 km2) or less may be unsatisfactory when areas of 50 000 square miles (130 000 km2) or more are to be put under control as too many man hours of professional and auxiliary staff would be required to obtain the necessary data for evaluation. Therefore, modifications of these methods and statistically valid sampling procedures may be necessary. Adaptation of methods proposed

93Checking of every single breeding site after treatment has commenced, over a large area may prove beyond the capabilities of any team that could be put in the field. Therefore, (1) sampling of larval populations could possibly be restricted to selected sites after treatment to assess the reduction in larval population following control; (2) dissection of female flies collected at selected sites should be carried out to determine density, physiological age and infectivity within control areas. All flies thus collected should be retained for identification and as large a proportion as possible dissected. Use of aircraft

94The total area should be subjected to a preliminary aerial reconnaissance to enable the area to be divided into sub-areas which can be covered by a qualified person according to the peculiar topographical difficulties. For example, in savanna areas, it has been found that an entomologist can cover effectively for ground survey and control 100 miles (160 km) of river per year. This represents only a small part of a focal area and will permit a calculation of the number of personnel, transport, etc. to be made at an early stage in the Project.

95Aircraft should be available throughout the scheme to be used for the following tasks:

  1. locating possible breeding sites under all rlverine conditions;
  2. observing present tracks and roads and planning others necessary to reach the rivera;
  3. transport of the entomologist in charge around the project area to maintain close liaison with the other personnel involved;
  4. aerial larviciding, especially in breeding sites otherwise inaccessible;
  5. aerial adulticiding, if the necessity arises. Alternative insecticide and insecticide formulations

96DDT persistence and recycling is a serious problem as this material may accumulate to toxic levels in fish and other organisms. Consequently a scientist should monitor the effects of treatment on fish and other aquatic life.

97The exclusive use of DDT raises the problem of resistance. Susceptibility levels should be established at the beginning of the programme and their trend should be followed while it is in progress. This will require special facilities.

98The possible deleterious effect of DDT on the aquatic biotype combined with the possibility that resistance may develop to DDT, make it imperative that satisfactory alternative insecticides be sought for by a screening and field testing programme.

2.4.2 Other problems

99Sero-immunological methods might be of great help in evaluation but methods suitable for large-scale use under field conditions have yet to be developed.

2.5 Conclusions

100From the epidemiological and entomological viewpoints, it has been demonstrated that onchocerciasis control is technically possible in Africa. Adequate control of the vector S. damnosum can be achieved using the methods already available, and this alone will result in a very great reduction in transmission.

101The effects of vector control could be greatly enhanced if this method could be supplemented by chemotherapeutic control designed to reduce the microfilarial reservoir in the human population. However, the drugs at present available all suffer from disadvantages which limit their use on a large scale, and there is urgent need for further research to develop new filaricides active against O. volvulus.


102While it is technically possible to achieve onchocerciasis control with the methods now available, the question remains as to whether or not it is feasible, i.e. under what set of circumstances is control practicable, justified and advisable. In order to answer this question, a detailed examination of the needs for control and of the related economic, technical, financial and organizational aspects is necessary. Afterwards it can be decided where and how a proposed project can be carried out with the maximum chances of success and benefit to the population concerned.

3.1 General economic considerations

3.1.1 Needs for economic considerations in public health

103In most tropical countries a dynamic process of development has taken place covering a multitude of fields ineluding public health improvement. However, as the financial and manpower resources of these countries are usually very limited, a sound economic approach to development planning is an essential requirement which applies equally to public health development schemes. Consequently, socio-economic factors have to be considered from the beginning in the planning and programming of health activities. There are, in particular, three points which call for reasonably accurate information on the economic impact of a disease, the cost of its control and an estimation of the control benefits:

  1. the establishment of priorities in the planning of health programmes;
  2. the procurement of assistance in the financing of specific disease control programmes;
  3. the interrelationship of health development with the country's over-all development plan, in particular with projects like water and/or agricultural development schemes which may have a direct bearing on health.

104The economic effects of controlling different crippling diseases should be taken into account when weighing up the technical reasons for choosing to mount one sort of disease campaign rather than another. Priorities must be established in relation to practicability, costs and probable benefits to the human population. These priorities could well be different from one region to another and from one morbid condition to another.

105The aim of bringing an economic concept into public health planning is relatively new and there is not much previous experience and knowledge of its mechanisms. It requires the co-ordination of different disciplines which still have to learn each other's way of thinking and language as well as gain the full understanding of each other's problems. A new methodology has to be developed which satisfies all the various scientific elements and which will lead to the information aimed at.

3.1.2 Common conditions of parasitic diseases relevant to assessment of their economic impact

106Most parasitic diseases have a number of conditions in common which have an influence on the economic aspects and thus justify the separation of this disease group from others in regard to the assessment of its health implications:

the majority of parasitic diseases occur at present in developing countries of the tropics where frequently no state social security organization exists which could provide a sufficient source of reliable data;

they are predominantly diseases affecting rural populations for which social, economic and health information is often difficult to obtain. At the same time it is the rural communities which are involved in agricultural improvement plans;

the clinical manifestations of many parasitic infections are of a chronic nature developing slowly without a dramatic onset. Hence they are frequently overlooked with the result that morbidity data are unreliable sources grossly underestimating the actual situation; the pathological changes of several infections are still under investigation and the establishment of their public health importance is still in progress;

in many instances the parasitic diseases are water-related infections, that is, their degree of transmission is influenced by the proximity of water. Hence, development programmes such as agricultural irrigation, creation, of lakes, etc., will have a bearing on the distribution and level of endemicity of many parasitic diseases; the same applies also to uncontrolled urbanization;

apart from the direct effect of the infection on man, there exists also an indirect effect on the community involving elements such as nutrition, demography, social structure, etc

3.1.3 General considerations of economics in the appraisal of health problems

107In the context of development planning an appraisal of health problems from an economic point of view is required primarily as a basis for advising on the establishment of priorities within the health budget. It can also be envisaged that a private or international financial organization which receives a request to finance a health programme by loans is likely to interest itself in the narrow economic returns of such a programme, e.g. by means of cost-benefit analysis.

108It should be emphasized that cost-benefit analysis cannot be applied to all health policy decisions in developing countries. In particular, we are unable to calculate the value of a human life but, nevertheless, we should make a great error by not taking this value into account by considering it as nil, solely because we cannot give a precise answer to the question.

109It is true that any economic policy implies a precise evaluation of costs, and that we must develop the analysis of costs in the framework of health programmes. The main difficulty lies in the evaluation of nett advantages or benefits.

110This difficulty does not appear only in health policy. More generally, it concerns a great part of the economic policies of developing countries, in which it is impossible to apply cost-benefit analysis in the way that this technique has been used for the study of specific projects in North America and Western Europe. This is due to two series of factors

  1. by their very nature, developing countries have not reached a stage of stable economic organization where present costs and prices of inputs and outputs can be used as terms of reference. Large development projects, for example, inevitably change wage levels and prices throughout a substantial part of the economy of a developing country;
  2. particularly in developing countries, one must consider a number of strategic choices rather than a single project. The nett benefits of any of these projects will depend, to a crucial extent, on complementary and supplementary action on other fronts.

111When a private commercial firm or financial organization is requested to finance a programme - even a health programme - it is likely to focus its attention, for example with the aid of cost-benefit analysis, on the direct economic returns of the programme. But economists, and particularly development economists, are not absolutely obliged to use narrow quantitative criteria, particularly when this technique is reducing the usefulness of their analysis. Their aim is to present choices between suitable costed alternative projects. Agricultural development, for example, has a high priority rating in most developing countries, and comparisons between various possible uses of natural resources would be useful.

112In the field of health policy, one should bear in mind that, even if it is impossible to evaluate a human life, an immeasurably positive effect on rural populations might be obtained simply by demonstrating to them that Simulium damnosum can be controlled.

113Attention must therefore be focused (a) on the practicable policy choices concerning people afflicted with a variety of parasitic diseases, and (b) on obtaining information about areas and costs of research and about partial and specific benefits; e.g. from curing onchocerciasis and preventing blindness due to this disease.

114The projects could range from relating the costs of research on onchocerciasis control to the question of whether a depopulated valley should be resettled or the development of a programme combinfng several mutually interacting public health measures,

115This general framework being clarified, it is useful to reaffirm the absolute necessity of gaining better knowledge of different aspects of the economic impact of each health programme. For example, the evaluation of benefits of onchocerciasis control will turn mainly on the increased employability of healthier men. At the same time, however, specific investigation of the economic effects of preventing blindness due to onchocerciasis seems to offer scope for a reasonably precise appraisal.

116It is however important not to consider individual projects apart from each other, but to keep in mind alternative feasible programmes, and to establish for each programme the time sequence or planning of expenditure. In particular, it is always important to link any health project to general socio-economic development policies, and specially to socioeconomic planning. Onchocerciasis control policy must be a part of general health planning, which in turn must be a part of socio-economic planning. This is equally true in regions where at present no specific development programmes exist, but where it is necessary to control parasitic diseases.

3.2 Criteria to be considered in the selection of an area

117The principles on which priorities for a control project area should be decided include the following:

  1. the area must include foci of high onchocerciasis endemicity with high rates of morbidity, particularly blindness;
  2. the presence of the disease must constitute a severe economic drain on the community, particularly by denying use of fertile land in river valleys and by producing local depopulation;
  3. there should be evidence from past experience that Simulium control therein can be carried out effectively and at reasonable cost;
  4. there should be available a high human population density in nearby zones, which can repopulate and develop any land reclaimed by control operations;
  5. there should be economic or development projects envisaged in the area which would benefit from Simulium control;
  6. the government or governments of the countries concerned must be anxious to institute control, to co-operate with one another in this respect, and to create conditions favourable to the smooth running of control operations;
  7. it is desirable that experience gained in the control area should be likely to prove of practical application to other river systems later on;
  8. there should be available basic epidemiological, entomological, topographic, hydrological and sociological data on the area concerned, information which can only be accumulated over some years of careful recording,

118It is recognized that investigations, carried out for the purpose of collecting information required to assess whether the conditions prevailing in a particular area meet the above criteria, are lengthy and expensive.

3.3 Selection of recommended area

119In considering where financial-aid for onchocerciasis control projects could best be given with the prospect of producing the greatest return in terms of benefit to the human community, it is profitable to consider all those regions of the world in which the disease is endemic and then to proceed first by a process of elimination, and later by a positive pproach to select a suitable control area.

120In the context of the present meeting the onchocerciasis areas in America were excluded, because it was believed that some of those organizations which might consider financing onchocerciasis control projects would be to a great extent committed to using their resources on the continent of Africa. However, it was noted that in America, especially in Guatemala, the existing programme for the control of onchocerciasis (Robles' disease), which is based oh nodulectomy, is in urgent need of international assistance so that operations may be extended particularly in the field of entomological control. Technical advisers, particularly an entomologist for a 1-2 year assignment, complementary salaries, ophthalmological equipment and vehicles are needed. The meeting accordingly recommended that the Pan American Health Organization and the office of the Agency for International Development should be asked to give urgent consideration towards supporting and extending the programme of onchocerciasis control in the Americas.

121The endemic area of onchocerciasis in Africa may, broadly speaking, be divided into two epidemiological zones extending east-west across the continent. There is a forest zone to the south where the disease is widespread but in which the infections, even when intense in dermatological manifestation, are only occasionally associated with blindness; and there is the savanna zone to the north, where, in many localized areas of intense transmission, onchocerciasis is responsible for blindness rates of 10% and more and has caused the inhabitants to desert many fertile river valleys. It is in this savanna zone that control is most urgently required and it includes foci of blinding onchocerciasis of differing size and importance which are known to exist in Senegal, Mali, Guinea, Upper Volta, Ivory Coast, Ghana, Niger, Dahomey, Nigeria, Cameroon, Chad, the Central African Republic, the Democratic Republic of the Congo and the Sudan Republic.

122It is considered that the proposed first large-scale control scheme must be carried out under the best conditions obtainable so that it may be given every chance of success and thus prove to be an exemplary precursor to more extensive operations throughout the whole African savanna zone.

123For a variety of reasons the foci in those countries lying in the eastern half of the savanna zone do not appear at present to offer conditions suitable for a large-scale control programme.

124The group of foci lying in Senegal, western Mali and Guinea were considered as highly deserving of attention but suffer at present from the disadvantages of seasonal lack of access to the Senegal focus and shortage of basic entomological data in some of the foci which would take several years to collect.

  • 12 WHO Regional Office for Africa project AFRO 0131 carried out by an Onchocerciasis Advisory Team, f (...)
  • 13 Fonds d'Aide et de Coopération du Gouvernement de la République française.
  • 14 Fonds européen de Développement, du Marché commun.

125There remained then the infamous foci of onchocerciasis situated in the centre of the West African savanna zone and embracing parts of Ghana, Upper Volta, Togo, eastern Mali, Ivory Coast, Dahomey, and Niger; and it is indeed fortunate that choice of these areas should at the same time be supported by many positive arguments. The selected area is outlined on Map 4 and for it a great deal of the basic entomological and epidemiological data necessary to a control programme are already available. The scourge of onchocerciasis shows its sorry effects on the economy of the countries, the suffering population is potentially industrious, active and desirous of progress, and in so far as naturel barriers against reinvasion can be said to exist in.the zone, the area is relatively well protected. In addition, well planned small scale control schemes are already in progress in this zone of evident priority. Two schemes are at present under progress: the first one is sponsored and put into effect by the governments of Ghana, Togo and Upper Volta (with the participation of OCCGE teams in the case of Upper Volta) and with the effective collaboration of WHO.12 The second one is under the charge of three States members of OCCGE, Mali, Upper Volta and Ivory Coast, with assistance from FAC,13 FED14 and ORSTOM, and with WHO's support (for research and development) In fact, a substantial financial effort is already being made by the countries in the recommended area.

126It was considered that aid for onchocerciasis control could be given with maximum effect to a scheme designed (i) to unite and consolidate the control measures already effective in this area, (ii) to extend the operation so as to cover the whole of headwaters of the Volta system and the tributaries of neighbouring river systems from which reinvasion of S. damnosum may be expected, and (iii) to maintain the scheme for period of 10-15 years so as to permit the Virtual elimination of the parasite O. volvulus from the human population, meanwhile integrating operations with the health services of the countries concerned.

127The hope was expressed that control operations would later be extended both to the east and to the west of the recommended zone; and that further meetings would be held at a later date to consider means of effecting this.

128Finally, consideration was given to the existing state of affairs in other zones wherein onchocerciasis is widespread and of severity as a blinding disease but where the basic data and infrastructure necessary for control are not yet available.

129Among those in West Africa were the foci in Senegal, in the west of Mali and in north Guinea. It was noted that many basic data on the last of these areas have been collected by the joint mission organized by the Governments of Guinea and of the Federal Republic of Germany in 1963-67, but that at present there was a lack of sufficiently trained staff to undertake control. Along with them, the foci in Nigeria, Uganda and Sudan were also considered as areas in which it would be desirable to collect further data so as to interest those institutions, which, in their desire to encourage economic development of Africa, might consider giving further aid to onchocerciasis control.

3.4 Economic considerations in the recommended area

130There are the usual difficulties in presenting figures from African countries; mainly, in this instance, those of evaluating the proportions of areas and populations that are actually exposed to Simulium bites and onchocerciasis infection. For purposes of collecting information, the recommended zone was arbitrarily divided into six parts, and Table 1 below gives figures many of which, it must be realized, are approximations.



* Includes Sikasso town, 20 000.

131The various sectors are inhabited by farmers principally raising food crops. These farmers are in the main capable of substantially increasing their productivity provided that the accessibility of the endemic zones, the dissemination of improved agricultural techniques, and the organization of market outlets permit.

132The zone comprises the worst focus of onchocerciasis in the world, with local blindness rates of up to 15% and all the other ill-effects of onchocerciasis highly prevalent. Blindness is commonest in males over 30 years of age, and 20-25% of these may be blind in a seriously affected village. The labour force is correspondingly depleted. The age-sex population structure shows a marked deficiency in the young male age group. These young men have little incentive to remain at home where fertile land on which to cultivate food and cash crops is denied to them and, in consequence, many of them migrate in search of better economic conditions, e.g. to cocoa farms, mines, etc. of Ashanti or Southern Ivory Coast. As a rule, they return home eventually. However the combined weakening of labour effort resulting from blindness in men in their prime and from migration of young adults can very easily result in a village community starving from simple lack of agricultural manpower.

3.4.1 Estimated costs of onchocerciasis control

  • 15 Detailed costs will be provided after the first short-term survey referred to in Annex 2.

133The cost of onchocerciasis control in the recommended area, based on present expenditures for existihg control services and control operations carried out in the area might reach US$ 2 512 000 a year at its outside limit.15

134Expenditure for the recommended area will be on a substantial scale. However, because control would be more effective when covering a large area and, depending on a wellestablished time-table of operations the total duration of the campaign could be shortened it may be possible to reduce the estimated cost to US$ 2 million or even 1.5 million.

3.4.2 Benefits anticipated from onchocerciasis control


135In the whole area there are approximately 626 000 persons infected with onchocerciasis, of whom approximately 52 000 are blind. The other effects of heavy onchecerciasis infection, pruritus, debility, probably scrotal elephantiasis, etc., have been described in detail on many occasions. They add up to a great sum of human misery. The first - though not the earliest in time - effect of onchocerciasis control will be the relief of suffering and an increase in the work capacity of the community.

136The potential increase in communal work capacity can be partially calculated. Blindness falls mostly on adult males over 30 years of age, and one may estimate not too fancifully that the removal of onchocerciasis would in the future for this reason alone make fit for work 20 to 30 thousand men who would otherwise be an economic liability.

  • 16 Société d'Etudes pour le Développement économique et social, Paris.

137Secondly, the population structure of onchocerciasis foci (where it is known) shows a marked deficiency in the young male adult groups. For example, in the Upper Volta rural areas the proportion of adult males to females is 100:143 (SEDES16 report, 1965). In Tumu district, Ghana, the proportion of males to females in the 15-39 years age group is 3:4. In Frafra district, Ghana, there is the even more striking male-female ratio in this age group of 15:26 (Ghana population Census 1960).

138Admittedly if the young men are emigrating, they are working somewhere. Nevertheless, restoration of well-being in the onchocerciasis areas and the release of farming land at present uninhabitable would offer more inducement to remain at home. One may assume that a normally balanced population structure is a desirable objective.

139The sum of human inefficiency due to the other effects of onchocerciasis is not calculable without ad hoc investigations that have not yet been undertaken. Anyone with personal experience of living among onchocerciasis sufferers knows well enough that considerable debility is caused.


140In the course of the project several hundred men will receive training in epidemiological and entomological techniques, carried out in field conditions. These men will constitute a very great contribution to the health infrastructure of the region, and an asset to be reckoned on when campaigns against other mass endemic diseases are planned.

Access to water

141The savanna zone is traversed by many rivers, but for most of the year is otherwise dry. The mere fact that life can be made possible closer to rivers constitutes an economic benefit in transport of water - either by human power or mechanical means.


142At present virtually the only fishermen in the whole area are immigrants. They prefer to dry their fish and export it towards the coast. Economic development in the region would create a demand for this source of valuable protein.

Protection of labour forces in development projects

143It is necessary to protect labour forces working on hydro-electric and irrigation projects from Simulium attacks and from onchocerciasis. Key personnel, whose services are essential in the construction of major capital works, have a dread of onchocerciasis which has to be taken into account. In the area of Kainji dam in Nigeria, the cost of Simulium control has averaged $ 70 000 a year.

Psychological effects

144The control of Simulium and of onchocerciasis will be an unmistakable demonstration to the people of the area (who suffer probably the heaviest load of endemic disease of any community in the world) that amelioration of their conditions of life is indeed possible, thus creating an atmosphere favourable to plans for increasing productivity.

3.4.3 Benefits anticipated from redevelopment of river valleys

145Table I (see above) shows that in the recommended area the unused land capable of being put to agricultural production amounts to 1 090 000 hectares. Care has been taken not to make this figure grossly optimistic. For example in Upper Volta 300 000 hectares of unused land could be developed for pastoral use.

146A general indication of the additional farm revenue obtainable in Upper Volta, taken as a whole, can be gained from the following table.

Type of farming

Annual revenue/hectare (US$)

1. Traditional subsistence farming on plateaux


2. Traditional subsistence farming in valleys


3. Traditional supervised (co-operative) farming operations


4. Modern mixed farming schemes:
(a) dry cultivation
(b) irrigated


147In Northern and Upper Ghana it appears that the productive value of land is somewhat higher:

Potential gross value per hectare of rain-fed crops, Ghana


Annual revenue/hectare (US$)

Guinea corn and millet




Ground nuts (shelled)


Rice (in grain)


Cow peas


Tobacco (dry leaf)




148It is stated that these yields could be doubled by irrigation.

149Tentative calculations can be made of the gross annual income at different yields per hectare. It must be assumed that each additional hectare under active cultivation by traditional methods requires the work of two adults. The table below provides an indication of alternative combinations of manpower and yields per hectare which would provide sufficient revenue to offset the upper estimated annual cost of Simulium control, i.e. $ 2.5 million a year.

Estimate of annual gross revenue (US$ millions) according to different combinations of yields and hectares under active cultivation

Estimate of annual gross revenue (US$ millions) according to different combinations of yields and hectares under active cultivation

150It can be seen that 60 000 men would need to produce between $ 80 and $ 100 a year by traditional agriculture to offset the cost of Simulium control, whereas at yields of $ 40 a hectare, more than 120 000 men would need to be employed.

3.4.4 Conclusions

151While the costs of Simulium control for the whole area may seem considerable, nevertheless the benefits to be expected both in human and material improvement are sufficiently great to encourage the belief that a campaign for the control of Simulium would be worth while from an economic standpoint and further justified since population increases rapidly in areas close to onchocerciasis foci.

152It is still necessary, however, to verify and complete certain sources of information both about estimated costs and, more especially, concerning the potential benefits to be obtained in different parts of the recommended area.

153At the present time the only dossier which exists, although it is not complete, concerns the Volta Basin and its adjacent areas.

154The dramatic improvement in human well-being that will follow the control of Simulium is not open to doubt. Nevertheless, it must be emphasized that any onchocerciasis control activity that is not accompanied by organized economic development of the reclaimed lands (including better farming methods to increase cash revenues) will fail to enable the countries benefiting therefrom to take charge of the maintenance of control after the initial phases. The associated economic studies must therefore pave the way for the beneficiary countries to participate in, and later assume in full, the financing of the campaign. It is essential that international organizations mainly concerned with agricultural development in tropical countries should be consulted and their participation sought in programmes that will be associated with the control of onchocerciasis.

155It is of course a sine qua non that the first move in the search for sources of financial aid to carry out widespread and costly control measures should come from the government or governments of the countries concerned.


4.1 General principles

156A mass campaign against onchocerciasis should aim at the eradication of this endemic disease. Although this may prove technically difficult, it is imperative that a degree of control such as to render impossible any serious - especially ocular - complications should be attained. It should make possible resumption by the riparian populations of a life that is normal in every respect, and even resettlement in the area if the scourge of onchocerciasis has driven them away from it.

157A reduction in vector density such as has been obtained by certain larviciding campaigns already in operation is, by itself, capable of lowering the transmission potential of the vector Simulium population to a point where severe eye complications - impaired vision and blindness become very rare.

158In practice, there will be no difference in the methods used to achieve eradication and maximum control of the vector. The different phases to be planned and the resources to be brought to bear are the same in both cases.

159Even in an extensive regional-type focus, if the natural or artificial barriers are effective, if insecticiding activities have been properly carried out and evaluated throughout the treated zone, it should be possible to attain a satisfactory end result with the virtual elimination of transmission. This may be obtained either by elimination of the vector (e.g. S. neavei in Kenya) or by complete control in all breeding sites (e.g. Victoria Nile or Sikasso area), or even by slow attrition as in the Budongo area (Uganda).

160The operational phases of a campaign against onchocerciasis will be in some ways similar to the well-mapped-out phases of a campaign against malaria:

  1. Preparatory phase;
  2. Attack phase;
  3. Maintenance phase.

161Adequate evaluation must be made throughout the campaign.

Preparatory phase

162Its duration should be at least three years and it should provide for the following:

163(1) An adequate survey of human onchocerciasis prevalence should be made by existing health personnel using standard methods as recommended by WHO (see section 2.2.2). If the survey cannot be carried out by existing health services, teams specially trained for the purpose should be formed. Standard maps should be drawn up with conventional signs showing the degrees of infection at the district level (districts coloured or marked in black and white according to the prevalence and severity of the disease, as far as possible). These maps should be kept up to date as accurately as possible (using medical record cards) in every hyper-endemic focus. Experience has shown that national major endemic disease control services are the most suitable bodies for drawing up such exhaustive inventories, for which they generally have the necessary experience and equipment.

164In hyper-endemic foci a full-scale ophthalmological survey by a specialist is indispensable before undertaking larviciding.

165(2) Collection of all necessary data on topography, climatology, hydrology and entomology (see section 2.2.1).

166(3 Advantage should be taken of this period for recruitment of staff, for their specialized theoretical and practical training, and for their installation. This applies to necessary staff at all levels.

Attack phase

167This should follow immediately the preparatory phase. Control methods (e.g. insecticide treatment, damming of rivers, etc.) found effective in the preparatory phase, will be applied according to the methodology developed during that phase. Technical responsibility will be exercised by the chief entomologist, as the specialist responsible for the antivector campaign, on the understanding that all the necessary logistic means have been placed at his disposal in due time together with adequate facilities for maintenance treatment.

168In an extensive regional type project it is impossible to specify precisely in advance the duration of the attack phase. Flexibility must be allowed for in regard to certain procedures and even to the duration of the attack phase, for experience has already shown that. Imponderables - in particular anormal rainfall, unforeseen difficulties in vector surveys both at the larval and adult stages, etc. - nearly, always arise.

Maintenance phase

169The duration of this phase will be long if eradication of the vector proves difficult to achieve. Normally the maintenance phase will be the responsibility - with or without outside assistance - of the beneficiary States that have participated in the regional campaign. Its annual cost should be much lower than that of the preceding phases. Under the responsibility of the States, it can be taken in charge by the national staff trained during the mass campaign.

4.2 Time-table and phasing in the recommended area

170The time-table is deduced from the preceding general principles applied to the local conditions. The recommended area contains not only foci where the vector population is present all the year round but also areas where for part of the dry season it is not present. In the sequence of operations the permanent breeding foci, and especially those in which breeding persists during the dry season, must be attacked first.

171When funds, personnel and equipment are available, the following programme could be followed:

  • 17 WHO Rgional Office for Africa project AFRO 0131 carried out by an Onchocerciasis Advisory Team, fi (...)
  • 18 Fond européen de Développement, du Marché commun.

1st Year:


Control in area of AFRO-0131 project;17


extension of control to Comoe-Leraba area (FED project);18


continuation of control in Sikasso and Korhogo area (FED project).

2nd Year:


Continuation of 1st Year's programme;


last surveys and planning of control in Black Volta/Bougouri-Ba area.

3rd Year:


Continuation of 2nd Year's programme;


Initial control of Black Volta/Bougouri-Ba area (FED project and AFRO-0131, Ghana).

4th Year:


Continuation of 3rd Year'sprogramme;


review of contact zone east of AFRO-0131 project area (Niger and Northern Dahomey foci).

5th Year:


Continuation of preceding programme;


initial control of eastern contact zone (Niger and Northern Dahomey foci).

6th Year:


Continuation of 5th Year's programme;


evaluation of results.

7th Year)

8th Year)

As 6th Year.

9th Year)

10th Year:


Dependent on results;


possibilities of national services adopting the responsibilities for maintenance service.

172Note: Concerning the eastern zone, which comprises the western Niger foci and the northern Dahomean focus, control will be possible only after the permanent breeding sites of Ghana and Togo have been treated (see first paragraph of section 4.2). Moreover, the complete survey and collection of data have yet to be achieved.

173The timing of the hoped-for extension of operations outside the initial control area into Guinea, Senegal and other countries will be dependent on the rapidity with which basic information is provided from these zones and it cannot be stipulated in advance (see requirements for operational phase, section 2.2).

4.3 Organization and staffing

174For operational reasons the following organization is proposed in the recommended area:

4.3.1 Headquarters Functions of headquarters

175The planning, direction, co-ordination and administration of the campaign, as well as the training of staff devolve upon headquarters. Planning must be based on required entomological and epidemiological data collected during the initial field surveys. Co-ordination is needed between onchocerciasis control services and also between them and all services or agencies interested in rural, industrial and economic promotion in the area. This is especially true in the case of all the water-development projects.

176Specific functions of headquarters include: logistics, accounting, cost-analysis, collection and analysis of data, exchange of information, assessment of the campaign. Headquarters staff

177The staff at headquarters consists of:

  • the Project epidemiologist and the Project entomologist responsible for the total onchocerciasis control operations;
  • a consultant ophthalmologist who will assist, at all phases of the project in the planning of epidemiological investigations on morbidity (see 2.2.2) and assess survey data on prevalence and severity of onchocercal eye lesions; consultants for special technical fields as required by epidemiological circumstances, as well as consultants during the staff training period;
  • to each the Project epidemiologist and the Project entomologist is attached a junior to provide inter alia for liaison periods;
  • a finance administrator (and necessary staff);
  • a vector control engineer;
  • a hydrological engineer.

178Headquarters needs also common services for the operation of the project, such as:

  • mechanics, aircraft personnel (subject to the development and approval of aerial spraying techniques, some of the field teams would be replaced by aerial units, with resulting changes in organization), a statistician, draughtsmen, secretarial and clerical staff;
  • a central laboratory (parasitology and entomology). At least two technicians are required, one of whom must be a technician in chemistry. Operational organization

179For surveys and control operations, field units should be organized as follows.

4.3.2 Entomological units

180Vector surveys to collect data before, during and after treatment (see 2.2.1) and control operations are carried out by entomological units according to the project plan.

181Each unit is superVised by an entomologist. At the unit's base, the entomologist is assisted by the following staff; an entomological assistant, an administrative assistant to handle routine work such as finance and supplies, a secretary, two drivers and six general labourers.

182A unit would comprise two to four teams. Each team would consist of: one field officer, three or four field assistants, five drivers, 12-18 labourers.

183The number of teams that could normally be included in an entomological unit would depend not only on the area and rivers concerned, but also on the quality and reliability of the individual field officers and their supervisors.

184Each field team could command a stretch of river 100 miles (160 km) in length making the unit responsible for a minimum of 400 miles (640 km). Such a unit is capable of dealing with approximately 30 000 km2.

185An entomological unit would be responsible for the pre-control surveys and assessment in its area. Once larviciding is begun the same unit wouid carry out both the dosing of the rivers and the assessment techniques.

186The entomologist in charge of a unit ought to be authorized to concentrate at any moment as many of his teams on a given part of his area as the situation requires.

187Whenever possible the entomologists in charge of units should be relieved of routine administrative duties.

188Every six or eight entomological units will need to be organized into groups, headed by the most skilled and experienced entomologist of the group. A group would be responsible for the supply of the units below it and also form the base for heavy, specialized equipment, e.g. aircraft, radio links, road building equipment, etc.

189Entomological groups should be loosely connected so that exchange of equipment and supplies and information can take place. Maximum liaison between groups is essential.

4.3.3 Epidemiological unit

190The epidemiological unit is composed of two teams, each team comprising: one medical officer epidemiologist trained in basic modern epidemiological methodology with parasitological background; two male nurses; two technicians; two microscopists; two drivers and one labourer.

191The epidemiological unit is responsible for carrying out epidemiological work as required under the plan of operations established by headquarters, i.e. an initial prevalence survey and detailed surveys in indicator areas (see section 2.2.2).

192The initial survey will have to investigate a large number of communities in the country. If this cannot be conducted by existing services, two teams will be organized during the first year to determine the prevalence of onchocerciasis and blindness by investigating clusters of 200 persons and covering 2% of the population.

193When Simulium control commences, the teams will conduct the detailed surveys in selected indicator areas. An indicator area should be inhabited by approximately 250-500 persons, whom it will probably take about one week to examine.

194There will be an interval of two to three years between detailed surveys, during which the teams may be used to undertake chemotherapy for onchocerciasis under ophthalmic supervision. Apart from assisting in the planning of surveys and assessing ophthalmological data, the consultant ophthalmologist attached to headquarters (section will join the teams for survey work and for providing ophthalmic treatment as required.

195Although some progress has been made in the nomenclature and classification of eye lesions due to onchocerciasis, there are still differences of opinion between specialists in this field. The meeting therefore agreed that it was important that the services of the same ophthalmologist should be obtained for both the initial and all follow-up detailed surveys.

196The following work schedule for epidemiological investigation carried out under the Project plan is suggested:

  • one year for the initial survey by two teams (200 persons per day during 20 days a month, which equals 48 000 persons per year per team, i.e. approximately 100 000 persons in one year if two teams are at work;
  • hall a year for the first detailed survey by the epidemiological unit covering one indicator area of 250-500 persons per week, i.e. 18 indicator areas;
  • 15 year follow-up programme:
  • re-survey of indicator areas at two to three year intervals;
  • onchocerciasis sample surveys as in the initial prevalence survey covering those parts of the project area not previously surveyed;
  • treatment under ophthalmic supervision of individual patients who risk becoming blind from their existing load of onchocercal infection (see section

4.3.4 Training

197There is a world-wide scarcity of all types of trained personnel required for parasitic diseases and especially in the field of onchocerciasis. Specialized training in Simulium/onchocerciasis control will be needed at all levels. It is highly important that training candidates should possess an aptitude for field work, a willingness for hard work and a readiness to put up with rough conditions. Whenever possible, preference should be given to personnel with previous experience of vector-borne disease control. As far as possible, training should be arranged at institutions within the area of the control project and preference should be given to locally-recruited staff provided that they have the necessary qualifications; however, in areas where qualified candidates are not available in sufficient numbers, recruitment will have to be made from a much wider field of candidates.

198Training should be organized on the following principles:

  1. Only two categories of staff should be considered for advanced training:
    1. professional staff;
    2. technicians/field officers.
  2. Priority should be given exclusively to training to meet the requirements of the project.
  3. The training courses should be given at the Project headquarters and be in the charge of those responsible for the project (entomologiste, epidemiologists, etc.). The best training for Simulium control is acquired in the field.
  4. The training period for professional staff will last three months and for technicians six months, the time in each case being divided equally between laboratory and field.
  5. The training of the personnel will be in direct relationship to their respective responsibilities.
  6. For entrance into the project and training course, the basic qualifications considered desirable are as follows:
    1. Epidemiologist: Medical graduate with special training in epidemiology or an entomologist with knowledge of parasitology and epidemiological methodology;
    2. Entomologist: Graduate with basic knowledge of entomology and parasitology, preferably with Masters degree or equivalent;
    3. Technician/field officer: Minimum: middle school graduate or state certificated (male) nurse with specialized training in entomology; possessing attributes essential for field work.
  7. Training of all other staff will be carried out locally.

4.4 Transport, equipment and supplies

4.4.1 Transport

199Three types of cars and trucks are necessary:

  1. long-wheel based four-wheel-drive station wagon and/or pick-up;
  2. lorry - one-and-a-half to three tons;
  3. car suitable for travelling the trunk roads of the area.

200For an entomological unit, the following number of vehicles would be required at the unit's base: (a) one car; (b) two all-wheel-drive station wagons or pick-ups; (c) two lorries; (d) eight bicycles; (e) one boat with one or two outboard motors.

201Each team would require: (a) four all-wheel-drive station wagons; (b) two lorries; (c) bicycles; (d) two boats with three outboard motors.

202This takes into account necessary replacement while maintenance and repairs are being carried out. The boats should be of lightweight construction but robust and portable.

203The number of planes required for the project will be directly related to the size of the area and the problems it poses. The campaign must have a full-time pilot-engineer and a mechanic to fly and maintain each project aircraft.

204Full and adequate repair facilities as well as spare parts for the engines of all motorboats and vehicles on the project must be furnished to provide against break-down, especially once control operations have started.

205The vehicles, boats, outboard motors, etc. should be depreciated over two years in view of the high mileage and rough terrain covered by entomological teams.

206Each epidemiological team will require three Land Rovers or similar vehicles.

4.4.2 Equipment

207Laboratory equipment - The headquarters laboratory must be fully equipped with the necessary optic apparatus, etc. and spare parts for replacement and the general needs of the units.

208Each professional or field officer should have at least one dissecting microscope and one binocular microscope (with immersion lens) plus all the necessary laboratory equipment and supplies (this must include all the material necessary for catching files etc. in the field).

209Field equipment:

  • Adequate camping equipment;
  • hydrological and topographical equipment;
  • ophthalmic equipment;
  • simple equipment for radio-communication between units and teams would be. highly desirable.

210Office equipment - For headquarters, units and teams.

4.4.3 Supplies

211Laboratory supplies; insecticides; drugs for the treatment of ophthalmic lesions; drugs for mass chemotherapy whenever effective, non-toxic compounds are available.

4.5 Existing services (in the recommended area)

212In the member countries of OCCGE there exist public health organizations known as the Services des grandes endémies which are responsible for the control of endemic diseases. These organizations are staffed by auxiliaries supervised by local medical officers where available. In addition these countries have the support of French doctors and entomologists of the OCCGE. At the Centre Muraz at Bobo-Dioulasso (OCCGE) the Onchocerciasis Section specializes in long-term research on the biology, ecology and distribution of the vector (S. damnosum) as well as in epidemiological studies of onchocerciasis in the member States of OCCGE. This section maintains or has maintained at various times, sub-stations at Ouagadougou and Garango (Upper Volta, Korhogo (Ivory Coast), Bougouni (Mali), Natitingou and Parakou (Dahomey. The Onchocerciasis Section is directed by a medical entomologist from ORSTOM, who is assisted by two other ORSTOM entomologists (at Bobo-Dioulasso and at Ouagadougou), by several ORSTOM technicians (at Korhogo and Bobo-Dioulasso) and by a technical assistant of OCCGE (at Bougouni). In addition, this section is responsible for the organization, direction and execution of the FED/OCCGE campaign against the vector of onchocerciasis. A certain number of specialized personnel (technicians from ORSTOM and from FAC) also work within the framework of this section. Dahomey and Mali both have their own entomologist.

213In Ghana the Division of Epidemiology at the Ministry of Health is responsible for the control of communicable diseases. Apart from the headquarters units there is a Medical Officer of Health responsible for communicable diseases control in each region. The headquarters organization has a vector control unit from which entomological work is organized. This is at present under the supervision of a senior research entomologist from thé Ghana Academy of Sciences. Routine survey work is undertaken by auxiliaries of the Rural Health Service who form part of the regional health organizations. The Volta River Authority has its own health organization and there is an entomologist in this organization, who works on Simulium control. He has his own staff of auxiliaries. The Institute of Aquatic Biology at the Academy of Sciences also collects information about Simulium during its routine work. The work of all these organizations is co-ordinated by the medical officer in charge of the Epidemiological Division through a Committee.

  • 19 Other services provided by WHO under regional programmes of assistance to countries for operationa (...)

214The WHO project AFRO-0131, staffed by an ophthalmologist/epidemiologist and an entomologist, and based in Ghana, is assisting the governments of Ghana, Upper Volta and Togo in the preparation of a plan for an inter-country onchocerciasis control project in the area of the White and Red Voltas (Map 4)19

  • 20 In preparation.

215The existing services for countries outside the recommended areas are described in a separate document20 along with the distribution of onchocerciasis in those countries.


  • 21 Wld Hlth Org. techn. Rep. Ser., 1966, 335, 45-48.

216The recommendations of the WHO Expert Committee on Onchocerciasis21 (see Annex 3, section 6) on the subject of research needs in onchocerciasis were endorsed, and it was suggested that the following items should be added:

  1. The clinical manifestations in the younger age groups up to five years should be carefully investigated;
  2. The possible role of the parasite in producing an arrested development (pseudo-nanism), and its impact on general health should be studied;
  3. Reliable and more specific immuno-serological methods for detecting onchocerciasis under field conditions should be sought;
  4. More effective, non-cumulative, cheaper insecticides should be developed as well as formulations to improve their dispersion and carry;
  5. Accurate information on the role of Simulium biting density as a determining factor in the abandonment of fertile land should be collected;
  6. The antifilarial action, pharmacology, and toxicology of Mel W require study. Special attention should be paid to the mechanisms producing encephalopathy and to ways and means of avoiding it.22 For instance, further research should be carried out on the use of Mel W in association with antihistaminic drugs or possible detoxicants in an attempt to find a dosage schedule which may be less toxic and more effective against the adult worms of O. volvulus and free from frequent, serious risks of encephalopathy;
  7. Every encouragement should be given to the development of new drugs effective against O. volvulus with especial emphasis on the need for non-toxic macrofilaricidal preparations.


217The meeting made the following recommendations:

2181. Co-ordination will be necessary between the governments of the countries within boundaries of which the recommended area lies, in order to synchronize and strengthen anyapplication for financial assistance which may be made to outside sources; once financial resources are assured for the continuation and extension of existing control operations, it would be desirable that the responsible public health officers and financial controllers of the countries concerned should meet to agree on ways and means for ensuring effective co-operation among themselves so as to attain their mutually desired objective of controlling onchocerciasis with the utmost expedition.

2192. Whereas the magnitude of the recommended programme places it beyond the present fiscal and manpower resources of the countries involved, and whereas the nature of onchocerciasis control excludes any effective action on a piece-by-piece basis, the programme must be accepted in its entirety, therefore the attention of the three sponsors of the meeting should be directed to this fact and they should be urged to pursue energetically the procurement of the needed resources from whatever sources possible, be they national or international, bilateral or philanthropic. Contributions of funds will afford greatest flexibility and freedom of action but provision of personnel, especially those of most specialized qualifications, is highly desirable and even necessary.

2203. All current operations for onchocerciasis and Simulium control within the recommended control scheme area, and elsewhere, should be encouraged, maintained and, where possible, extended.

2214. Training Centres for entomologists and technicians to be employed on Simulium control in the recommended area and in adjacent zones should be organized without delay.

2225. An international study mission should be formed at an early date, with the following brief:

  1. to assemble and analyse all the existing information relevant to a technical and economic study of onchocerciasis control and regional development;
  2. to provide a more detailed assessment of the costs and benefits expected from the proposed programme of onchocerciasis control in the recommended area, especially in combined regional rural development projects including health, agricultural and industrial activities.

223It is recommended that a suitable team for the mission would comprise two experts in onchocerciasis, an agricultural development expert, an economist and a socio-demographer. The team should be bilingual French/English. A working programme is provided in Annex 2.

2246. Although an appreciable amount of information has been gathered in recent years, knowledge of the geographical distribution of onchocerciasis and its vectors should be completed as soon as possible and exact quantitative epidemiological data collected throughout the endemic area on a uniform basis. In particular, every assistance should be given to promote the training and provision of personnel to collect such data as rapidly as possible in the onchocerciasis zones into which it is hoped to extend the present recommended control operation.

2257. The control project should be utilized as much as possible to encourage field research. Full use should be made in this respect of the research institutes existing in the countries in the recommended project area.


226Control of the disease onchocerciasis depends on the control of Onchocerca volvulus transmission and at present this depends largely on controlling the vector Simulium damnosum by means of larvicides. Much information is now available indicating that control of onchocerciasis in the savanna zone of West Africa is feasible, and it is considered that the time is now ripe to undertake a large-scale Simulium control scheme for the purpose of reducing the prevalence and intensity of onchocerciasis among the people living in this zone. Such control would stop the further occurrence of onchocercal blindness, which under present conditions is such a frequent sequel to the infection, having dire socio-economic repercussions on the afflicted communities and obliging them to abandon much fertile land in river valleys.

227For the reasons given in section 3, the area centred on the head-waters of the Volta River and contiguous river basins is recommended as the one which should receive priority for a large-scale control project. Operations in this area could, if successful, be extended later to embrace neighbouring onchocerciasis foci in the African savanna zone.

228As it is likely to be beyond the means of the governments concerned to put the proposed scheme into operation, considerable financial aid will have to be sought from outside sources.


1 Wld Hlth Org. techn. Rep. Ser., 1966, 335.

2 A detailed description of the onchocerciasis situation country by country is given in a separate document (in preparation).

3 For geographers, the division between West and Central Africa is approximately the valley of the Cross River in Southern Nigeria. Reference to other onchocerciasis areas in Africa is also made in section 3.3 of the present report.

4 Greenslade, C. (1956) Incidence and causes of blindness, London, British Empire Society for the Blind, p. 5.

5 Wld Hlth Org. techn. Rep. Ser., 1966, 335, pp. 51-78

6 Wld Hlth Org. techn. Rep. Ser., 1966, 335, pp. 15-24, 28-45

7 Solvent: Heavy aromatic naptha with fuel oil added to give a specific gravity of about 0.995 and with 0.5% Triton X-161 added as a surfactant to aid initial penetration.

8 Wld Hlth Org. techn. Rep. Ser., 1966, 335, 31

9 Wld Hlth Org. techn. Rep. Ser., 1966, 335, pp. 16-24.

10 Wld Hlth Org. techn. Rep. Ser., 1966, 335, pp. 16-24.

11 A review of "Research problems involved in vector control methods" is appended (Annex 1)

12 WHO Regional Office for Africa project AFRO 0131 carried out by an Onchocerciasis Advisory Team, financed under the United Nations Development Programme (Technical Assistance).

13 Fonds d'Aide et de Coopération du Gouvernement de la République française.

14 Fonds européen de Développement, du Marché commun.

15 Detailed costs will be provided after the first short-term survey referred to in Annex 2.

16 Société d'Etudes pour le Développement économique et social, Paris.

17 WHO Rgional Office for Africa project AFRO 0131 carried out by an Onchocerciasis Advisory Team, financed under the United Nations Development Programme (Technical Assistance).

18 Fond européen de Développement, du Marché commun.

19 Other services provided by WHO under regional programmes of assistance to countries for operational surveys and control operations or under the headquarters research programme covering the whole field of onchocerciasis (including research projects supported in the recommended area) are not referred to in this report as they do not specifically apply to the proposed control project.

20 In preparation.

21 Wld Hlth Org. techn. Rep. Ser., 1966, 335, 45-48.

22 WHO Expert Committee on Filariasis (Wuchereria and Brugia infections) (1967) Second report, Wld Hlth Org. techn. Rep. Ser., 359, 25, 39.

Table des illustrations

Légende * Includes Sikasso town, 20 000.
Fichier image/jpeg, 154k
Titre Estimate of annual gross revenue (US$ millions) according to different combinations of yields and hectares under active cultivation
Fichier image/jpeg, 36k

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