Tracking infectious diseases

1If you can’t look for it, you’ll never find it. Or rather, we can only find that which the tools at our disposal allow us to see. Which helps to explain why, throughout history, biologists have frequently struggled to identify pathogens. The first to be discovered were parasites such as worms, visible to the naked eye. Thereafter, the invention of the microscope and the development of growth media made it possible to identify bacteria, and molecular methods allowed scientists to analyse micro-organisms which cannot be easily cultivated in growth media. More recently, the advent of PCR 16S has allowed for further progress in detecting bacteria which are very hard to cultivate using more traditional techniques.

2But researchers are a long way away from achieving anything like a comprehensive inventory of infectious diseases, especially since the line between what does and does not constitute a pathogen is often a blurry one. Perhaps the most famous example is staphylococcus aureus, a bacterium frequently found on the skin where it is generally harmless, but which can provoke violent infections in certain circumstances. In fact, in many cases a pathogen only becomes a pathogen when its host is in a particular state or situation: the pathogenicity of an organism is defined by the complex relationship between man and micro-organism.

3This observation has prompted researchers to look more closely at the human body’s most substantial bacterial reservoir: the intestinal flora. The idea behind this approach is that certain pathologies could be connected with the bacteria in our gut, something which has only recently been demonstrated for two diseases commonly arising in connection with malnutrition: kwashiokor and nutritional marasmus. These conditions are both widespread in Mali, affecting 10% of children under the age of five. Worldwide, these diseases afflict more than 50 million children and cause hundreds of thousands of deaths every year.

••• New methodological approaches are allowing researchers to gain a new perspective on the concept of pathogenicity. •••

© Ird / O. Mediannikov

4Analyses have revealed that these deadly conditions are connected with changes in the internal microflora, which make it impossible to cure some cases even when the sufferers receive emergency nutrition. But, according to researchers, a simple faecal transplant could help to rebalance the intestinal flora and boost chances of survival.

5Discoveries like this are the reason why researchers have now embarked upon a project to establish a full inventory of the intestinal microbiota, not necessarily to identify potential pathogens, but rather to study and better understand the composition of a healthy digestive flora. This would simplify the process of identifying irregularities which might help to explain certain chronic fatigue symptoms, or even more serious illnesses whose causes still remain mysterious.