Most Hollywood supervillains have nothing on the malaria parasite, not just for its horrendous death toll, but the devious way this single-celled organism outwits our body's defenses. Now one of its secrets, the way it makes infected people more attractive to mosquitoes, has been revealed, opening the way to countering it.
Members of the Plasmodium genus, like the malaria parasite, have a lifecycle that requires them to be transmitted by Anopheles mosquitoes, but to multiply in the red blood cells of vertebrates. Since the victims will either clear most of the parasites from their system or die, malaria needs mosquitoes of the right species to bite an infected individual while the parasites are common enough in the bloodstream to be transmitted on.
Mosquitoes, at least the females that use the blood to feed their eggs, don't need any incentive to bite their prey. However, from the parasite's point of view, they need to make sure the mosquitoes are biting the right people, the ones that have been infected. It has been known for more than a decade Anopheles mosquitoes prefer to feed on people infected with the parasite, but until now we have not known how this occurs.
A study in the Proceedings of the National Academy of Sciences has revealed infected children produce increased amounts of heptanal, octanal, and nonanal; organic compounds called aldehydes. The authors confirmed the scent of these chemicals' attractiveness to mosquitoes by mixing them with body odor from healthy people and testing the insects' preference.
Some other diseases, not transmitted by insects, also cause people to produce extra aldehydes. However, the authors found the specific aldehydes measured in this study are unique to malaria infections, suggesting this is an evolved response of the parasite, rather than a coincidence mosquitoes are attracted to smells we make when we are sick.
“A possible application of our work is in odor-bated traps for monitoring or mass-trapping of malaria vectoring mosquitoes,” study author Dr Jetske de Boer of the London School of Tropical Medicine told IFLScience. Moreover, de Boer added, it may be possible to use the discovery to diagnose malaria using smell alone (probably using electronic devices rather than the human nose), replacing blood tests.
“There’s a great need for non-invasive diagnostic tools for Plasmodium and improved monitoring of mosquitoes, which are both very important in eliminating malaria,” she said.
De Boer thinks it less likely it will be practical to suppress aldehyde production, other than through malaria treatments, as this isn't the only way mosquitoes find their victims. However, she thinks masking the smell might work.
Sadly, the work probably won't resolve the perennial question of why, outside malaria zones, mosquitoes leave some people alone while making life miserable for others.