Which animal is the most dangerous to humans? the mosquito. A simple mosquito bite may result in death. And the mechanisms of malaria, for example, are still poorly understood. However a new study, conducted at the University of Fribourg, has now shown how the parasite influences the disease. The results of the study will enable there to be a reduction, not only in fatalities, but also directly in the number of infected mosquitoes.

There are 300 million infected individuals in the world and more than 3 billion people at risk: malaria is still one of the major public health challenges of the 21st century. Caused by a parasite of the genus plasmodium and transmitted to humans via the bite of infected mosquitoes, the most serious cases cause the death of half a million people every year, a large number of whom are children under 5 years of age and pregnant women.

Though the majority of infected individuals recover completely, some patients develop serious symptoms, such as cerebral malaria, severe anaemia or respiratory distress, which can be fatal. These clinical symptoms are caused during the blood stage when infected red blood cells burst, secreting or releasing a number of toxic substances produced by the parasites. Recent studies have noted the important role played by extracellular vesicles (VEs), coming from infected red blood cells, in regulating the course of the disease. Indeed, the concentration of VEs in the blood serum of patients infected by the plasmodium parasite is higher than in the control group of non-infected subjects.

A question of communication
So the parasite communicates with the human body via these vesicles, but how? It is these mechanisms which an international  research team headed by Dr Pierre-Yves Mantel of the Institute of Anatomy at the University of Fribourg and Professor Matthias Marti of the Harvard School of Public Health have just discovered. The identification of these mechanisms opens the way to the development of new therapeutic strategies which will enable not only a reduction in patient mortality, but also a direct reduction in the transmission of the parasites to mosquitoes.

This team had already demonstrated that infected red blood cells secrete tiny vesicles which enable and aid the transmission of the parasites to mosquitoes and consequently the survival of the plasmodium parasite itself. Indeed, it seems that the parasites communicate with one another via these vesicles, which allows them to synchronise.

However, the molecules responsible for the transmission of the Information contained within the VEs remained unidentified. In a new publication in the prestigious scientific journal Nature Communications, Dr Pierre-Yves Mantel and his team show that the VEs transmit molecules of RNA, the regulators of the infected cells, to the cells of the blood vessels. The microRNA thus transmitted are capable of regulating gene expression in the target cells and can thus modify the function of the blood vessels.

• Link to the article in Nature Communications