Carbon dioxide emitted from humans and other mammals is a well-known homing beacon for blood-thirsty female mosquitoes. But mosquitoes responsible for spreading the parasite that causes malaria, Plasmodium falciparum, are more attracted to already infected animals.
Ingrid Faye and colleagues at Stockholm University now report that (E)-4-hydroxy-3-methyl-but-2-enyl pyrophosphate (HMBPP), a molecule made by P. falciparum, explains this mysterious attraction that helps spread malaria.
They showed that mosquitoes preferred to consume red blood cells laced with HMBPP, doubling their intake compared with HMBPP-free cells. “It was a very fast feeding and they filled their guts enormously,” Faye says. Blood cells infected with P. falciparum caused a similar increase in feeding (Science 2017, DOI: 10.1126/science.aah4563).
By analyzing the volatiles emitted from red blood cells, the researchers showed that HMBPP raised CO2 emissions by 16%. The molecule also increased the release of aldehydes, such as octanal, nonanal, and decanal, as well as monoterpenes, such as α-pinene, β-pinene, and limonene. Adding a synthetic blend of these compounds plus CO2 to blood cells had the same mosquito-enticing effect as HMBPP.
The scientists also determined that HMBPP altered transcription of genes expressed in mosquito neurons, suggesting that the parasite molecule further influences mosquito behavior and blood-seeking preferences. Faye hopes to investigate HMBPP’s nervous system effects in future studies.