Malaria: Parasite calls mosquito taxi by body odor

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MunichThe malaria pathogen is ingenious. In order to leave his old host and infest new ones, he has to rely on mosquitoes as a means of transport. To attract them, he uses a trick: he orders his "mosquito taxi" via a scent signal.

Plasmodium - this is the name of the parasite that causes malaria. According to the World Health Organization, 207 million people were affected by it in 2012, and 627,000 died of it. Reason enough for research to take a closer look, above all, at the transmission routes. Because the pathogen actually has a very complex cycle: it has to be in the right place at the right time - and in different hosts. For this, the parasite is dependent on Anopheles mosquitoes as a carrier. In order to increase his chances that a mosquito will bite his home host and that he can eventually use it as a "taxi", he manipulates its smell. At least that was the result of an experiment by researchers from ETH Zurich and Pennsylvania State University with mice.

Sex cells who love to travel

To do this, the scientists exposed mosquitoes that were ready to bite in a wind tunnel. Its gentle breeze showed the insects the way to two chambers, each with a mouse. One rodent was healthy, the other had been injected with plasmodia. The flight of the mosquitoes led purposefully to the infected rodent. This was especially true when the parasites had formed a large number of gametocytes - a kind of sex cells that need a mosquito intestine in order to fuse with other gametocytes.

However, the plasmodia do not seem to stimulate the production of a novel substance - the researchers at least could not find any components that were only present in infected mice. Rather, the odor composition of the host changes: "Various substances that we already know that mosquitoes are attracted to were to be found more often," explains study leader Mark Mescher. That's smart because “Mosquitoes don't benefit from biting infected people. It therefore makes more sense for the pathogen to intensify a scent mark that mosquitoes are attracted to anyway, ”says Mescher.

The scientists were surprised to find that the body odor was longer. Even when infected animals no longer showed symptoms of malaria, their scent profile revealed that they were carrying the pathogen. However, not all stages of the disease smell the same. The odor of the acutely ill differed from that exhibited by individuals in later stages of the disease.

Non-invasive diagnostic tool

The researchers want to try out soon to what extent their results can also be transferred to humans. Because if sick people could actually be recognized by their smell, that would also offer new ways of identifying infected people quickly and easily.In particular, those individuals could be discovered who no longer show symptoms, but still serve as a reservoir and carrier of the pathogen. (lh)

Source: De Moraes C. et al. Malaria-induced changes in host odors enhance mosquito attraction. PNAS, 2014; DOI: 10.1073 / pnas.1405617111

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