More attractive to mosquitoes due to malaria infections

Infections with the malaria pathogen attract mosquitoes

07/01/2014

An infection with the malaria pathogen influences the host's fragrance and makes it more attractive to mosquitoes, according to a recent study by researchers from ETH Zurich (Switzerland) and Pennsylvania State University (USA). Scientists have studied the effects of unicellular malaria parasites on the odor profile of mice and their findings in the journal „Proceedings of the National Academy of Sciences“ (PNAS).

Malaria is transmitted by the Anopheles mosquitoes. The life-threatening disease is caused by animal protozoa of the genus Plasmodium, which, however, according to the researchers have a problem. Because „In order to complete their life cycle, they have to get back into a mosquito.“ Only when the insect stings an already infected victim, it can take in the pathogens and start the life cycle from scratch. The research team led by lead investigator Mark Mescher has now demonstrated that the pathogen, however, it „Do not leave it to chance if the mosquito finds the right victim.“ By influencing the characteristic scent mark of the host, this will be more attractive to hungry mosquitoes.

Malaria pathogens make the scent of the hosts for mosquitoes irresistible
As part of their study, for example, at the end of a wind tunnel where mosquitoes were placed, the researchers had each set up a chamber with one infected and one uninfected mouse. They then observed which chamber the mosquitoes preferred to choose. The test was repeated just under one and a half months daily and supplemented by further tests. It turned out that „For mosquitoes those infected mice were the most irresistible, having a high concentration of so-called gametocytes, the plasmodial sex cells, in their blood“, reports ETH Zurich. Accordingly, around two to three weeks after infection, the smell of the infected mice had the greatest effect on the mosquitoes. If the mosquito absorbs the gametocytes with the blood, these reproductive cells in the mosquito intestine start a new development cycle, so that the next bite of the mosquito can transmit the infectious malaria parasites. If the gametocytes are not taken up by a mosquito, they die and the life cycle of the malaria pathogens is interrupted.

Increased formation of different fragrance components
The researchers analyzed changes in the fragrance profile of the hosts using gas chromatography and found that „the pathogens do not trigger the formation of specific, unique fragrance components.“ Rather, any existing fragrance components would be increasingly formed. Mescher and colleagues could according to their own information „find no components that were only present in infected mice.“ Only the level of fragrances has changed. „It appears that the pathogen causes the increased formation of several fragrance components that attract mosquitoes“, explains Consuelo De Moraes, Professor of Biocommunication and Ecology at ETH Zurich.

Malaria infection affects the body odor for a lifetime
The researchers conclude that it makes perfect sense if infected hosts do not form highly specific fragrances, but only intensify the known fragrance profile in certain places. Because the malaria pathogens also have negative effects on the mosquitoes and these would have „no benefit of stinging infected people“, reports Study Director Mark Mescher. „For the pathogen, it is therefore more appropriate to strengthen a fragrance brand, are attracted by the mosquitoes anyway“, So Mescher on. Most of the researchers have surprised, according to their own information, „that the malaria infection affects the body odor throughout life.“ Although infected mice no longer had any symptoms, their personal scent rating indicated that they carried the virus. However, the odor profile in the different disease stages was quite different.

Hope for new diagnostic tools
Although the findings are not directly transferable to human malaria, they do suggest that „suggest that comparable scent effects cause mosquitoes to more easily infect humans“, the researchers write. In addition, the scientists hope that their findings as a basis for „a new non-invasive diagnostic tool“ could serve. Such „would make it much easier to check the population for malaria infections“, report Mescher and colleagues. In particular, that way too „those individuals who no longer show any symptoms but continue to serve as a reservoir and transmitter of the pathogen on the mosquito.“ (Fp)