An infection with malaria pathogens changes the scent of infected mice, making those infected more attractive to mosquitoes, researchers have found.
Malaria is and remains a formidable disease that is transmitted to humans by the anopheles mosquito. The pathogen is a protozoan of the genus Plasmodium. If left untreated, malaria can be deadly.
In order to complete its life-cycle, the plasmodium parasite must eventually be acquired by another mosquito, which occurs when the insect bites an infected person.
In a new study, researchers from ETH Zurich and Pennsylvania State University show that the plasmodium parasite appears to manipulate its host by changing the characteristics of the infected individual's body odour, which makes the carrier more attractive to hungry mosquitoes.
Mosquitoes were most attracted to infected mice with a high concentration of gametocytes, the plasmodium parasite's reproductive cells, in their blood.
When the mosquito consumes these cells along with the blood, a new development cycle starts in the mosquito's gut.
However, the pathogens do not appear to trigger the expression of unique scent components.
"There appears to be an overall elevation of several compounds that are attractive to mosquitoes," said Consuelo De Moraes, from ETH Zurich.
The researchers believe it is logical that infected people smell more attractive but do not form highly specific body odours, especially given that the malaria pathogen can also have adverse effects on mosquitoes.
"Since mosquitoes probably don't benefit from feeding on infected people, it may make sense for the pathogen to exaggerate existing odour cues that the insects are already using for host location," said study leader Mark Mescher.
What researchers found most surprising is the fact that the malaria infection leaves its mark on body odour for life.
Even when infected mice no longer had symptoms, their body odour showed that they were carriers of the pathogen.
However, not all stages of the disease smelled the same: the scent profile of the acutely ill differs from the profile found in individuals exhibiting later stages of malaria infection.
Although the findings cannot be directly transferred to human malaria, they suggest that similar effects might be involved in the attraction of mosquitoes to infected people.
In addition to aiding efforts to disrupt malaria transmission by mosquitoes, researchers hope that findings may also be used to develop new non-invasive diagnostic procedures that would facilitate effective screening of human populations for malaria infections, particularly in order to identify individuals who don't otherwise have symptoms but remain capable of spreading the disease.