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La lutte antivectorielle en France

 | 
Didier Fontenille
, 
Christophe Lagneau
, 
Sylvie Lecollinet
, 
et al.

Tools for risk management and anticipation

Research: a key to successful vector control1

Texte intégral

  • 1 In this chapter, references to the CD-ROM concern question 13: “How does research contribute to im (...)

1The history of research on vector control is dotted with successes and failures and it would be useful to draw lessons from these. One of the major successes is the onchocercosis control programme in West Africa. The source of this success: the intensive research on the vector species of blackfly (Simuliidae) and their biology, on the insecticides that could be used and on appropriate product rotation strategies, all accompanied by over 30 years’ intensive human and financial investment. The pioneering, highly multidisciplinary approach adopted achieved the effective control of the transmission of the disease, to such a degree that today it is no longer a problem for public health.

2In contrast, however, the attempt at complete global eradication of malaria by vector control, through a campaign run from 1955 to 1968 resulted in failure in the tropics (see CD-ROM). More recently, the introduction and diffusion of West Nile virus into the USA revealed a serious gap in knowledge of the disease. The same goes for the recent (2005-2006) chikungunya epidemic on Reunion Island.

3Vector control is usually underpinned by applied research, but it sometimes stimulates basic research on more fundamental scientific questions. The highly effective tools that are currently used (insecticide-impregnated mosquito nets, visual traps against tsetse (Glossina) and so on) are often the fruit of prior fundamental research performed in the many disciplines involved. Such research includes work in engineering, biological sciences, chemistry, epidemiology and biomathematics, but also in human and social, economic and political sciences.

KNOWLEDGE ON VECTORS LEADS TO CONTROL TOOLS

4If one believes in the saying “Know your enemy” to be able to fight him, then clearly it is essential that research on vector surveillance, biocidal products and on material and equipment be founded on sound knowledge of vector biology.

Vector biology

5Vector biology involves two major fields of research: “taxonomy” and “population biology”.

Taxonomy

6One of the prerequisites of vector control is to know how to identify the vectors and put them in an evolutionary context. To crystallize the issue, it must be borne in mind that nearly 900,000 insect species have now been recorded, representing more than 80 % of all animal species described to date. Around 10,000 new species of insect are described and published every year and an estimated two to three million species are yet to be discovered. As observations progressed, it became apparent that most vectors belonged to complexes of species that, although morphologically similar, were genetically different and hence reproductively isolated.

7In taxonomic research, multiple-entry identification software now compensates somewhat for the deficiencies and subjectivity of standard dichotomous keys. Molecular tools have also been developed, mainly based on the polymerase chain reaction (PCR) technique, which allow identification of most taxa. Such an approach using PCR tests in Tanzania and South Africa, when mosquitoes were still present after insecticide treatment, was able to show that only individuals of Anopheles parensis, Anopheles rivulorum or Anopheles vaneedeni, from the same group as Anopheles funestus but exophilic non-vectors, persisted whereas Anopheles funestus had been controlled. Sequencing of Ribosomal DNA, mitochondrial DNA or of introns and exons of nuclear genes has helped refine the phylogeny and phylogeography of many vector species. It has thus been shown that in the Camargue the populations of Anopheles hyrcanus and Anopheles pseudopictus make up a single species.

Vector population biology

8The genetic mechanisms behind vector competence are becoming better known thanks to quantitative genetics applied to insects and to functional genomic tools. The most rapid advances are being made in the knowledge on Anopheles gambiae, the major vector of human Plasmodium in Africa. Studies have shown that this mosquito, like other insects, develops cellular immunity involving haemocyte-mediated melanization and phagocytosis, and humeral immunity developed by the intervention of antimicrobial peptides. Its complete genome has been sequenced and partly annotated (see CD-ROM for other vectors and infectious agents).

9However, a major conceptual advance in entomology is the approach that looks at the dynamics of the vector system as a whole. This considers the system with all its components, the vector, parasite and host populations, all adapted at a given moment to an environment that changes. The study of vectors then becomes a component of eco-epidemiology. Considerable advances in population genetics of vectors recently achieved have improved understanding of the links between each of the actors of the system and helped to gauge better the important roles of coadaptation and coevolution.

10Substantial research has been done especially on vectors’ physiological, genetic, morphological and behavioural adaptations to environments that are changing, particularly in response to climate change and environmental modifications. The results obtained include findings on vectors’ choice of sexual partners, choice of resting site and breeding site in mosquitoes and identification of genes involved in behaviour and unravelling their expression mechanisms. They are largely owed to new tools from molecular biology, but also partly to a return to descriptive and explicatory studies on the behaviour and life characteristics of vectors (see CD-ROM).

11The socio-anthropological component is now also better integrated into the research. For example, the development and spread of dengue in Asia, South America and the Caribbean are clearly linked to urbanization and living standards. Similarly, reinvasion of housing by sylvatic triatomine bug vectors of Chagas disease helps explain why transmission persists even after application of vector control measures.

The history of tsetse trap development
■ The first methods for catching tsetse flies were rudimentary, but quite effective: capture traps, glue-impregnated screens.
■ 1930: first tsetse trap. This Harris trap is like an enclosing box with a cage fitted above equipped with an anti-return device.
■ 1970s: the traps underwent considerable development aided by studies on tsetse behaviour towards animals, odours and colours and other factors. Observations made discovered that: the shape and size of the trap influence capture rate (a single shape is not effective for all Glossina species), some species are sensitive to movements (hence the use of vehicles equipped with electrified mesh), tsetse can distinguish colours (some are attractive, like royal blue) and some are sensitive to odours (various substances can be used).
■ These observations culminated in the development of new traps, such as the blue and black biconical Challier-Laveissière trap, which is simple, lightweight, foldable, cheap and efficient especially for forest-gallery Glossina form, and in the blue cubic trap of Flint which can be used fixed to one spot against savannah tsetse.

Vector surveillance

12Vector surveillance, based largely on capture traps, aims to detect the presence of a vector or a given population (introduction of an exotic vector into a previously vector-free area) or to determine vector abundance useful for estimating the risk of transmission (see Box “The key parameters of transmission” in the chapter “From vector risk assessment to epidemic risk assessment”). The first operation (detection of vector presence) requires that traps be as sensitive as possible. In the second one (abundance assessment) the traps must reflect the diversity and quantity of the insects that feed naturally on the hosts concerned by the investigation.

13The literature abounds in descriptions of trapping methods. The history of those used for African Glossina (tsetse), sleeping sickness vectors, illustrates perfectly how research can further progress in this field (see Box).

14Scientists’ work leads to ways of designing traps best adapted for the objectives of surveillance, including traps with or without animal bait, others targeting only females, and egg-laying traps (see details on CD-ROM).

Biocidal products

15To be effective, biocidal products must change and develop perpetually owing to vectors’ acquisition of resistance and capacity for adaptation. Furthermore, the legislation insists that some of them should be abandoned.

The new insecticides

16Application of the European directive 98/8/EC has meant that most of the old effective, inexpensive biocides (generally the organophosphates and carbamates), non-notified or non supported by their manufacturer, have either disappeared (like temephos, malathion) or are about to be withdrawn (fenitrothion). As for the development of new products, one of the hindrances is that the market for them is not a priority in the eyes of the manufacturers, because its profitability is low.

17Considerations of cost, acceptability, safety and, more recently, respect for the environment have nevertheless led companies, research institutes and international agencies to offer new compounds such as insecticides of biological origin: Bacillus thurigiensis israelensis (Bti), effective against Simuliidae and certain mosquitoes, B. sphaericus (Bs), active against mosquitoes of the genus Culex, Spinosad, from the naturalite chemical class derived from actinomycetes, or pyrethroids, with low toxicity against homeotherms and, finally, growth regulators mimicking insect hormones (see Box).

18It remains that at present, few really innovatory avenues are explored. Some trials are nevertheless under way on natural substances such as essential oils or plant extracts (geraniol). Research laboratories are working on new biocides (chemical or bacterial) resulting from screening on specific target nuisance arthropods. Some have given rise to the filing of patents. However, the link between laboratory research and the agrochemical industries is not easy to forge. In addition, the development and marketing of a new product are extremely costly and not necessarily profitable for the manufacturer.

Sensitivity and resistance to insecticides

19Many vectors have become resistant to insecticides. Management of resistances to insecticides requires their characterization. Resistance is an adaptive phenomenon. It usually appears in a restricted area, but it can expand rapidly by active migration. But the main process is passive migration, seeing that mosquitoes can propagate far from their habitat aided by aircraft or ships. Their genetic adaptation is more-or-less effective depending on the mutated genes, the nature of the mutations and the selection pressure exerted.

Summary of insecticides used in France
Malathion, temephos and fenitrothion are no longer authorized in France.
Larvicides
Bti and Bs
– Utilization: a highly favourable toxicological spectrum and high selectivity.
– Limitations: Bti acts on most species of Culicidae, Bs is more specific for Culex and Anopheles.
– Changes and developments: diversification of formulations depending on diversity of situations in the field.
Diflubenzuron
– Action: development inhibitor.
– Utilization: used little or not at all at present, owing to its action mechanism which intervenes only at the moulting period.
– Limitations: significant effects on invertebrates.
– Potential uses: mainly targeted at species living in urban areas, improvised mixtures with other larvicides to be assessed.
Pyriproxifen and S-methoprene
– Action: mimics growth hormone.
– Utilization: effective at very low concentration. Used little or not at all at present, owing to its action mechanism which intervenes only at the time of emergence.
– Limitations: assessment to be made on effects on non-target aquatic invertebrates in their development period.
– Changes and developments: mainly for use in urban areas, improvised mixtures with other larvicides to be assessed.
Spinosad
– Action: causes modification of nervous system in many insects.
– Utilization: certified in some member-States against ravaging insects (agriculture), use anti-Cuclidian larvicide currently under assessment.
– Limitations: first assessments not very encouraging for use in natural environments owing to it effects on non-target aquatic invertebrates.
Imagocides
– Potential uses: in mosquito destruction or vector control programmes.
– Limitations: low selectivity of non-target insect fauna.
– Changes and developments: more than 20 compounds supported at Community level (European Union).
Deltamethrin
– Utilization: for spatial treatment and residual treatment.
– Changes and developments: a formulation is marketed as an aqueous emulsion. Effectiveness and selectivity trials under way with a view to replacing fenitrothion.
■ Other notified pyrethroids
– Utilization: could be incorporated into the composition of products devoted to non-specific domestic imagocide treatments (nuisance insects/arthropods commensal with humans).
– Limitations: cost of their authorization, growing resistance to pyrethroids (Kdr, cross-resistance with that of DDT).
Products requiring research
Natural pyrethrum (highly photolabile and allergenic, etofenprox (a non-ester pyrethroid), naled, one of the rare organophosphates notified (adulticide in spatial treatment), natural plant extracts and essential oils as repellents or insecticides.

20Considerable advances have been achieved over the past few years on the understanding of the genetic mechanisms. Two large types of the latter have been brought to evidence within mosquito populations. The first, called metabolic resistance, corresponds to an increased detoxification of the insecticide by enzymes which trap it and/or inactivate it before it reaches its target. The second corresponds to the mutation of the product’s target sites which change their conformation and affinity for this.

21Any light shed on these mechanisms can only improve vector control. In particular, the construction of resistant strains in an insectarium with a controlled genetic base allows the attribution, to a controlled mutation, of levels of resistance to different insecticides. The perfecting of detection tests for these mutations (biochemical or molecular) will offer the possibility of measuring their frequency in natural populations. These frequencies will be correlated with environmental factors (biocidal product treatments, ecological data and so on) and genetic factors (see details in CD-ROM).

Repellents and insecticide-repellent combinations

22The pollutant character of insecticides and the development of resistance to insecticides have led industrial companies, research institutes and international agencies to turn their attention to repellents. These substances are commonly used for personal protection against insect bites. They are now undergoing a revival of interest for public health purposes. Three control strategies are being studied at present: the use of repellents for dermal application on their own or as a complement to the wide use in the local community of impregnated mosquito-nets or other equipment, the impregnation of equipment just with repellents, and the use of repellent-insecticide combinations in reduced doses for the impregnation of equipment (for further information on the results obtained, see CD-ROM).

23Nevertheless, research focusing on repellents and their use in public health is just beginning. Fundamental research on olfaction and repellents’ impacts on insect nervous systems prove to be essential and urgent. Studies are currently being conducted on small molecules which act like antagonists of mosquito CO2 chemosensory-receptors. This opens the way to the development of new substances.

24Moreover, repellents are extremely volatile and hence the problem arises of their remanence on the impregnated equipment. Close collaboration between chemists, biologists and industry is imperative if research is to be undertaken that aims to formulate substances that meet well-defined remanence characteristics, particularly for long-lasting action. It is also essential to study the toxicology of products, used on their own or combined, as it is for any new compound. Then their effectiveness, again alone or in combination with other control methods, must be measured in the field at population level. This involves research questions in public health which entail experimental or quasi-experimental comparative assessment protocols, when a control programme is being implemented. The Department of Health set up a workshop group in 2008 in order to tackle these questions.

Unwanted side-effects

25Biocides might evidently exert unintentional harmful impacts on the environment, the study of which is in the field of ecotoxicology, but also on humans and animals, whose analysis requires research in toxicology. Resistance to certain families of insecticide could emerge or behaviour could change (avoidance). In parallel, the pressure exerted by the intensive use of insecticides and the fall in abundance of a vector can bring about worsening of diseases owing to the loss of immunity. All these aspects are dealt with abundantly in the chapter “Unwanted side-effects”.

Pesticides in agriculture versus vector resistance

26The use of pesticides in agriculture can be expressed by two direct effects on insect vector populations: by a non-specific action, these insecticides also kill vectors but in addition, which is more cause for concern, they select the appearance of resistance in the latter, by creating selection pressure.

27WHO and FAO experts recognized at the end of the 1980s, after 40 years of intensive use of organochloride (OC) and organophosphate (OP) insecticides in agriculture (particularly for cotton), evidence of selection of insect disease vectors brought on by agricultural plant health practices. Typically, populations belonging to 13 out of 48 anopheline species that had acquired resistance were presumed to have been selected by agricultural pesticides (see other examples on CD-ROM). Moreover, when agricultural treatments are deployed at the same time as vector-control operations, their relative significance for selection processes is not always easy to estimate.

28The identification and subsequent follow-up studies of the resistance gene for organochlorides and for pyrethroids (kdr gene) in anopheline populations have confirmed the continuation of selection processes of Anopheles by agricultural treatments in the Ivory Coast and Burkina Faso (see other examples and the literature on the subject on CD-ROM). Today chemical alternatives to pyrethroids in agriculture exist (spinosad, indoxacarb, growth regulators, but also other protection strategies (organically-grown cotton, genetically modified varieties), that could considerably reduce the impact of agricultural practices on the selection of malaria vectors. Regional mapping of the resistance of anopheline populations in relation to the strategies applied in the different crop systems would help to confirm this hypothesis.

29Fertilizers, especially modern products of the NPK type (nitrogen, phosphorous, potassium), can have attractant properties for gravid females of Aedes aegypti at certain concentrations: it would appear that the attractive power emanated by the NPK combination lies in a precise proportion of its component elements. Vigilance is needed in agricultural situations, but also in residential areas or gardens, and pot plants, which are often dressed with fertilizers. Thus, for Aedes albopictus, the chikungunya virus vector, the preferred breeding sites are indeed the saucers placed under the flower pots. Fertilizers are deployed in combination with insecticide treatments on all the crops.

30The principal mechanisms of resistance to insecticides are either mutations of the target, or metabolic resistance, which involves an increased level of detoxification of pesticides and pollutants by enzymes (for further information, see CD-ROM). It is therefore not surprising that in the large urban agglomerations in the tropics, Culex quinquefasciatus, observed in the most polluted sites, have become strongly resistant to most of the insecticide families, whereas generally no control campaign is run for this species by insecticides and pollutants. This is cause for concern, especially so seeing that recently colonization has been growing in anthropogenic and polluted sites in tropical urban environments by certain major vectors like Aedes gambiae, which transmits malaria in Africa.

Materials and equipment

31Each item of material used for vector control must be carefully studied and sized for optimum effectiveness, but also to limit unwanted side-effects.

32As far as spraying equipment and the conditions in which treatment is conducted are concerned, research concentrates on optimization with regard to new requirements governing hygiene and safety. Possible improvements to individual protection equipment (IPE) concern their ergonomics, considering the discomfort and arduous conditions experienced when working in humid zones or in confined environments (see CD-ROM). Another improvement, the fruit of a joint project between EID Méditerranée and the Institut de Recherche pour l’Ingénierie de l’Agriculture et de l’Environnement (CEMAGREF, Montpellier) concerns the setting-up of on-board DGPSs (Differential Global Positioning Systems) and the recording of flow rates before spray emerges from the nozzle. These two organizations are also combining their efforts to develop droplet generators that could optimize Bti aerial spreading.

33Aerial spraying campaigns, however, are up against the unfavourable image of their use in agriculture. They can continue only if accompanied by stringent measures (proof of their effectiveness, and the best possible control over treatment parameters). Trials are under way, under the leadership of EID Rhône-Alpes and EID Méditerranée (see further details on CD-ROM). In any case, whether treatments are conducted from tarpaulin-covered vehicles or by aerial spraying, temporal and spatial assessment must be made of their effectiveness (see Chapter 3 on vector control assessment).

34To date, impregnated materials (such as mosquito nets) still appear to be the most effective devices (and inexpensive), especially in the case of malaria. Clothing impregnated with pyrethroids or repellents and quite lastingly wash-resistant are currently being assessed. Several operational trials have shown, for example, that impregnated mosquito nets reduce malariainduced morbidity by about 50 % and deaths of children under 5 by 20 %. Large-scale utilization of impregnated materials is strongly supported by WHO and is incorporated in almost all national malaria control programmes.

35The research themes currently pursued include: third-generation mosquito nets (with permanent insecticide effectiveness for all their useful life), but also pyrethroid substitution products (the only ones used as toxicity for humans is low), against which vectors have developed resistance. Also investigated is the vector behaviour (host identification and biting), with a view to developing more effective tools.

CONTROL METHODS AND STRATEGIES

36How can epidemic risks be assessed? What strategies can be adopted? Answers must be found either in the existing research results or new research must be embarked upon.

Entomological and epidemiological indicators

37The relationships between entomological and epidemiological indicators provide essential information for improving management of vector control plans, for warning and for planning the control response. Research programmes are therefore necessary aiming to assess and validate different indicators, which supposes close collaboration between the entomology services, the surveillance organisms and research teams in epidemiology, biostatistics and modelling. The long-term idea is to share common tools for collection of georeferenced information.

38Remote-sensing tools can now contribute to following-up indicators. For example, the Argentinean Ministry of Health has assigned its national space agency, the Comisión Nacional de Actividades Espaciales (CONAE), to develop tele-epidemiology applications, jointly with the French space agency CNES, and to integrate the spatial products into the epidemic surveillance system. The objective is to use them in an early-warning system, in other words render them capable of detecting change in environmental and climatic conditions favourable for the development of vectors and to produce risk maps (intended for decision-makers and operational actors). The CNES is also involved in follow-up studies on rift valley fever in Senegal, as well as in a programme on urban malaria in Dakar, on the follow-up of dengue in Argentina and on the detection of malaria-infected zones in Brazil (for further information, see CD-ROM).

Risk assessment

39Risk assessment must take account, among other things, of those linked with global climate changes, but also of risks of importation, especially by means of transport. The risk indicators are currently poorly defined, which prevents the prediction of potential epidemics (see CD-ROM). This is where the European Eden project shows its interest, which jointly involves several research teams from the IRD, CIRAD, EIDs, the CNRS and universities to conduct studies and devise risk models (for malaria in the Camargue, for example). A risk study on rift valley fever (RVF) in Mayotte and Reunion Island was conducted in 2008 on the initiative of AFSSA. A group of experts coordinated by AFSSA gives advice, on commission and of its own accord, on regulations, then risks and operations associated with bluetongue in France. The ECDC commissioned a study of the risks of vector-borne diseases at European level and a report produced by an international consortium was delivered at the end of July 2008.

Genetic control

40Genetic control has already given rise to a number of successes (against screw-worm fly Cochliomyia hominivorax, for example, in Zanzibar). New research projects aiming to assess the feasibility of releasing sterile males of Anopheles arabiensis, malaria vector, and Aedes albopictus, vector of dengue and of chikungunya are being devised in Reunion Island and also in the Sudan and Italy. Besides this, the recent control of transgenesis in mosquitoes, the progressive identification of useful genes and the development of colonies of insects genetically refractory to a range of pathogens give a glimpse of the possible use of genetically modified mosquitoes incapable of transmitting viruses or parasites to humans. Other avenues are also explored, particularly paratransgenesis techniques taking advantage of symbiotic bacteria (of the Wolbachia type for example). Evidently, the use of transgenic mosquitoes necessitates detailed research upstream in order to ensure that the approach is feasible.

The means

41Experiments on the use of Wolbachia, endocelullar proteobacteria very widespread in the arthropods, were conducted for the first time in the 1970s. In mosquitoes, they induce cytoplasmic incompatibilities (CI) which lead to the premature death of their embryos (see the mechanisms on CDROM). Further experiments are now under way for infecting mosquitoes which are not naturally infected. The objective is to render them incompatible with the natural populations.

42Research projects on this aspect make it possible to envisage in the long run genetic control based on cytoplasmic incompatibilities, at least against some species and in certain regions of the world. Sequencing of the genome of Wolbachia from different species will contribute to improvement in our knowledge about the genes involved in incompatibility phenomena. These genomic studies could thus lead to the identification of new biocidal products.

Biological control

43Biological control consists of taking advantage of the natural enemies of insects. These include fish and insect predators, but also parasites or entomopathogenic agents. The first type includes larvivore fish and certain entomophage aquatic insects (see CD-ROM). Among the second type, can be observed some parasitic nematodes (mainly Ramanomermis cuilcivorax, others being assessed) or entomopathogenic viruses, but which are difficult to apply in operational terms. The microsporidia, however, do not hold any real interest. As for fungi, several species are potential candidates for use in mosquito control. Then there are the entomopathogenic bacteria which have such a high infective power against insects that their action can resemble that of insecticide: they have been used for several years now (see CD-ROM).

HUMAN AND SOCIAL SCIENCE RESEARCH

44Research in human and social sciences applied to vector control embraces a wide range of disciplines. Most of the time it is conducted in the framework of multidisciplinary programmes. The large disciplines of human and social sciences are essentially geography, history, social and political sciences, psychology, anthropology and economics.

Geography, history, psychology

45These are disciplinary approaches that must not be neglected. Geography, associated with planning (urban or agricultural), is indispensable: spatial location of biological and human processes, the notion of territory, scales, spatial analysis methods, disparities, fracture, continuities and so on. History is also highly important (knowledge of past epidemics and of control actions deployed), in the same way as the memorization of previous disastrous epidemics, must be taken into consideration: in particular, what do people remember and how are such memories passed down?

46Then there are the socio-political aspects, notably for what they imply in terms of governance and social debate. They are at the core of crisis management: role of the press, strategies of euphemization depending on how close the risk is, or, conversely, of minimization (for further information, see CD-ROM). Research work on vector control would moreover benefit from integrating that of psychologists, who could bring a relevant viewpoint on the levels of personal involvement of individuals.

Psychosociology

47Research projects in psychosociology are quite rare. The work that is done has two principal objectives. The first consists of identifying the perceptions of acceptability and effectiveness of vector control according to people’s sociodemographic characteristics. The second aims to bring into evidence a link, if one exists, between these perceptions, beliefs, feelings and so on, and the behaviour of actors exposed to vector risk and vector control. Such research would benefit from being conducted on different contexts of exposure and different levels of risk.

Other research

48Socio-epidemio-entomological research, when that is possible, comes as a complement to those mentioned. This field adds an entomological aspect which groups together observation data (on sites, vector capacity and density and so on) and also georeferenced data on vector control, essentially those concerning chemical and mechanical control methods.

The anthropological dimension

49This dimension is generally too often missing from research on vector control. Recent work has highlighted the value of “indigenous” knowledge and practices. These carry certain meanings/significance, which should be deciphered if campaigns are to be able to act alongside communities. Anthropologists consider that this distinction between common sense and specialist sense, between ordinary perceptions and scientific measurements does not mean that there are two mutually hermetic worlds. Concerning the health risks linked to environmental problems, there are no impermeable boundaries between scientifically based and popular discourses.

50Research work in the anthropology of health shows a frequent tendency to stigmatize people (because they “don’t understand” or are considered to be “not observant enough”), while omitting to consider the perceptions and practices of professionals in their relationship with their patients, for example. As far as vector control is concerned, it would be worthwhile, alongside studies on the knowledge and behaviour of communities (whether or not they support protective measures, whether or not they use these collective or individual measures), also to take account of the role of the various players involved in vector control (such as agents of the DRASS, officials) and of the medical profession in epidemic or endemic situations.

51These considerations bring out the fact that notions of areas or groups at risk are insufficient for taking into account the diversity of situations and scales of investigation. The idea of vulnerability, which expresses both natural and human situations, appears more appropriate.

52These thoughts suggest that the problems in question must be understood in a more general context, in particular by examining the interfaces between environment and health and drawing on more appropriate conceptual and methodological approaches (for further information, see CD-ROM).

Theoretical and applied economics

53The advances in theoretical and applied economics over recent years will have some significant spin-offs for vector control. Firstly, from now on it will be possible to improve economic assessment of strategies for prevention or treatment of patients. Secondly, these advances should help bring out the mechanisms that can be used to stimulate economic agencies (public or private) and therefore their behaviour in the context of vector control.

54Assessment of vector control policies and strategies is faced with the problem of assessing both direct and indirect costs (see also “Economic assessment: France lags behind”). The indirect ones are especially difficult to evaluate, as they are mainly borne by the patients, their family and friends and employers (owing to patients’ absenteeism or loss of productivity). Recent developments in methods seem promising: the willingness-to-pay approach, measurement of the externality costs (whether positive or negative), or the standardization of cost-measurement methods.

55Moreover, in the context of present rules of governance of vector control and their applications, deficiencies in behaviour are observed that could jeopardize the delegation of operation (public authorities or public-law bodies) or the implementation of prevention and vector control measures. Literature on improvement to the delegation relationship abounds, but the work described must be adapted to the French context of public health. Concerning the behaviour of private agents and their involvement in control measures, one of the major issues is to induce a greater responsibility among households and companies in a spirit of overall public good. Beyond awareness-building and information campaigns, that implies the introduction of incentive measures linking the actors involved in vector control and the private agents or communities of private agents. This means the establishment of contractual relations around an objective of a definite result in health terms (for further information, see CD-ROM).

ACTORS IN VECTOR CONTROL RESEARCH

56In France, and more widely Europe and the world, research on vector control is not highly coordinated. Projects stem most often from the individual initiatives of teams, whether in the public or private sector. Lines to follow or incentives on certain themes are sometimes given by the market (for example, a strong demand for repellents) and by funding sponsors, including the gates Foundation and WHO on malaria- and dengue-vector control, the CRVOI (Centre for Research and Intelligence of Emerging Diseases in the Indian Ocean) on chikungunya vector control or the European Union on malaria control. Some research projects can find their place in national calls for proposals of the French National Research Agency, in the broader framework of infectious diseases or the environment, but the applied-research aspect is more handicap than advantage in this case.

Industry

57Industry is not greatly involved in the research sector of vector control. The large chemical firms like BASF or Bayer either conduct or finance research, but mainly for agriculture, little for public health. Some companies, such as Bayer Environmental Service, wish to develop their activities in the public hygiene sector, but in the biocides sector, they restrict themselves to offering new formulations or presentations of existing active substances (generally from the pyrethroid family). Biocidal products (larvicides and adulticides) are still mainly agro-pharmaceutical by-products. Bti and B. sphaericus, exclusively specific for larvae of Culicidae or Simulidae, or nearly so, remain among the rare exceptions.

58Some companies have become engaged in the mosquito net niche, especially the insecticide-impregnated type, but their research is focused mainly on improvements to existing products. Others carry out studies, sometimes using non-standardized protocols, on the effectiveness of substances deemed to be repellent.

Research institutes and universities

59Many research institutes and universities are involved in the range of themes just mentioned, from basic scientific aspects (like vector biology) to social sciences considerations. The institutes or centres of research include the IRD, the CNRS, CIRAD, INRA and the Institut Pasteur. This research usually suffers from insufficient coordination. Each research team follows its own strategy to answer calls for proposals that might come from regional, national or international organizations or respond to the demands of industry (see the list on CD-ROM).

Vector control operators

60Vector control operators such as the EIDs, the Martinique département council or the Reunion Island public interest groups, carry out applied research on vector ecology, resistance to insecticides, new insecticides or new methods for the utilization and spreading of biocides, often working jointly with research institutes. They are naturally in contact with local people and conduct surveys on the acceptability of methods and on unwanted side-effects, especially their environmental impact.

Agencies

61Agencies such as the InVS, AFSSA and AFSSET have no mission to conduct research. Nevertheless, as part of their surveillance and health watch duties, they collect and analyse a large amount of data on the risks of infection for humans and animals, including vector-associated ones (whether zoonotic or otherwise) and risks for the environment.

62For example, InVS coordinates, leads and financially supports a 47-strong network of national centres of reference, several of them dealing with vector-borne infections. That Institute also has regional stations (inter-regional epidemiology units, including one covering the French Departments of America and another for Reunion Island and Mayotte). It is the designated national partner of the ECDC for European-level watch and early warning and it also runs a highly active international surveillance over emerging risks. It is therefore an important partner for public health research, whether for planned projects or emergency situations.

63In order to develop and adapt its surveillance systems, the InVS also works with academic research teams. Such activities hold particular interest for applied research, especially on the question of the link between entomological and epidemiological parameters, on monitoring, assessment of vector-control programmes and on modelling.

64AFSSA becomes directly involved in the work of mixed research teams, for example with researchers from INRA.

Funding agencies

65The funding agencies play an essential role in the orientation and performance of research. Not all of them can be mentioned here. The major ones, for French programmes are: WHO, FAO, the European Union, the national or regional financing agencies (ANR, CRVOL, AFSSET), the regional councils, industry, or foundations such as Bill and Melinda Gates and Wellcome Trust.

RECOMMENDATIONS
Global changes in climate, the environment and societies are bringing conditions in which some diseases are emerging, others are changing their distribution range and certain historically known diseases like malaria are undergoing a world-wide resurgence. Research must therefore focus on certain major themes:
– the mechanisms of vector transmission;
– assessment of entomological risk;
– transmission-control strategies that are less polluting, more accurately targeted and more durable.
Understand the nature of a vector
Compared with the number of species of arthropods that exist, pathogen vectors represent only a tiny minority. Studies on the taxonomy, biology and interactions between vector and pathogen which make use of data from morphology, morphometrics, biology, behaviour, genetics and genomics should be continued, especially within species complexes. The vector-parasite interactions are still an obscure area and must receive particular research attention.
Assess and predict vector risk transmission
Global changes are modifying or will modify vector density and distribution, their vector capacity and their contact with parasites and hosts. These changes can increase or decrease the incidence of a vector-borne disease. The first step must consist of a far-reaching investigation of risk indicators. Such research must then culminate in the development of risk assessment tools based on validated statistical and theoretical models. Particular effort must be exerted on transmission models involving a zoonotic reservoir, which are more complex than in the case where a single host is used.
Improve current vector control methods and develop new approaches
The biocidal control methods must be made more specific, less polluting and more effective. Joint research between entomologists and specialists in human and social sciences must be intensified with the objective of optimizing the acceptability of the methods proposed and the participation of communities. Concerning biological control approaches, even though most results have been disappointing, it is essential to continue research (with other bacteria, viruses, fungi, parasites, predators). As for genetic control, it opens promising prospects for vector control. French research teams must follow up such avenues in the framework of international joint projects.
Coordinate multidisciplinary research efforts
Vectors know no frontiers. Research therefore must be conducted at European, Mediterranean and sometimes global levels. In France, at present there is no true national coordination on vector control. An organization such as the Vectopôle in Montpellier could play this role of unifier of research, expertise and training at national or even European level. A specific call for proposals from the ANR on the subject of vector control in France could be set in place jointly by the ministries of Research, Health, Agriculture and Ecology.

Notes

1 In this chapter, references to the CD-ROM concern question 13: “How does research contribute to improving vector control?”.

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