The Antwerp Institute of Tropical Medicine has received a $3m grant from the Bill & Melinda Gates Foundation for malaria research. They will use it to attack malaria mosquitoes from a new angle.
Malaria is caused by a series of parasites of the genus Plasmodium. They are transmitted through the bites of several mosquito species. Eventually the parasites wriggle their way into our red blood cells, where they multiply. A few days later (the exact timing depends on the parasite species) the infected red blood cells burst and an enormous number of new parasites emerge, ready for the next round. High fever, anaemia, renal complications are common symptoms and cerebral malaria can be fatal if not treated in time. Each year some 800 000 people die from malaria.
In recent years the number of cases worldwide has come down; over a third of the 108 endemic countries decreased their malaria burden by half in the last decade. They achieved this by large scale indoor residual spraying of insecticides, massive distribution of long lasting insecticidal bed nets, and reliable diagnostics and treatment with artemisinin-based combination drugs. But this decrease is insufficient to eliminate malaria, as aimed by the World Health Organisation. Here the expertise of the Institute of Tropical Medicine comes in.
With current measures the number of mosquito bites can be brought down by 80 to more than 95%, but the remaining few percents are still sufficient to sustain the spread of malaria. Extra measures are needed to further restrict the distribution of the disease: by reducing the number of mosquitoes, by diminishing their chances to bite, and by fast identification and treatment of infected people so that mosquitoes no longer can suck infected blood from them. And we are running out of time: in some regions, for instance in Cambodia, the malaria parasite is becoming resistant against one of the most effective drug we have left: artemisinin.
One of the weak points of the current approach is that outdoor biting mosquitoes, and mosquitoes that bite early, before the people lie under their bed nets, are poorly controlled by bed nets, even though they cause a serious number of infections.
Professor Marc Coosemans and colleagues think they may have an answer. They now want to examine if that answer is powerful enough.
The scientists want to study if and how topical repellents, substances applied on the skin that chase away mosquitoes, can be used on a large scale to prevent the mosquitoes from biting early in the evening and outdoors.
If you ever have bought an insect lotion or spray, you know that a good repellent indeed keeps the mosquitoes away. But even though this diminishes your personal chances of getting infected, it does not diminish the malaria burden, unless other people are protected too. If the infected mosquito does not bite you, but simply deviates to your neighbour, the total number of cases remains the same. Prevention of malaria transmission only works if the mosquito during its lifetime cannot find another unprotected victim.
The individual effect of repellents applied on the skin is well studied, but the effects on the scale of a village, or larger, are not known. This is what the scientists of the Institute of Tropical Medicine (ITG), together with colleagues from Cambodia, want to find out, in a region with a high malaria burden. They want to learn if adding repellents to the current malaria control tools can indeed reduce the transmission of the parasite sufficiently to eliminate the disease. Or will more be needed? Their research must lead to a new strategic plan to make Cambodia free of malaria by 2025.
The scientists will study 100 villages in which people receive either the classical control measure of long-lasting insecticide-treated bed nets alone, or these bed nets with additional repellents. They will use the well-known repellent picaridine, one of the best now available against malaria vectors. The substance is donated by producer SC Johnson, a contribution of almost a 700 000 bottles of repellents. Chance decides which village gets what.
The villages will be followed for two years to buffer the effects of an unusually wet or dry season. A mobile laboratory will check the blood of the population with modern molecular biology (PCR)-technology. Infected people will be treated immediately. If during the study period an outbreak of dengue or another insect borne disease happens, the efficacy of the repellents in preventing those infections will also be assessed.
The researchers not only follow the number of infections, but also the impact of large use of repellents on the mosquito populations and its malaria transmission. The three million dollar question is: how much lower will the transmission be, and is that sufficient to break the chain of transmission?
At the same time the anthropologists of the team will look into the social and cultural aspects, because everything depends on the acceptance and use of the repellents by the population. Is it cool to use a lotion? Will they stay up longer because they feel safer? Do they accept information from Health Volunteers in the villages? Do they believe it helps? How can rubbing or spraying be incorporated in their daily habits?
The scientists will also record how they are used in real life conditions. Only then they will know if, repellents applied on the skin in addition to the use of bed nets are sufficient to bring down the transmission of malaria to elimination levels, or if still other measures have to be taken.
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