An investigation into the effects of Plasmodium parasite infection on the human odour profile

Some studies suggest that Plasmodium parasites can change the attractiveness of their vertebrate hosts to Anopheles vectors. This is suggestive of parasite manipulation, where the parasite alters a host phenotype to the parasite’s own fitness benefit. In this instance, Plasmodium parasites may benefit from increased transmission via a greater number of vector-host contacts. Despite evidence that variation in human host attractiveness to biting insects is manifest through differences in the human odour profile (volatile compounds produced by the skin), the association between odour profile and Plasmodium infection has never been studied in humans. The skin odour profile of individuals infected with Plasmodium in both experimental- and natural-infection settings was investigated using gas chromatography (GC). In the experimentally-infected (EI) cohort, adults were infected with Plasmodium falciparum and their odour profile sampled before, during and after infection. In the naturally-infected (NI) cohort, children aged 5-12 years with Plasmodium infections of varied parasite density, stage and species were sampled before and after treatment with antimalarials. Odour samples from both cohorts were further screened for infection-associated compounds using coupled GC-electroantennography (GC-EAG). In both EI and NI cohorts, changes in the production of several compounds in skin odour were found to be associated with the presence of Plasmodium parasites. Of these, production of the aldehydes heptanal, octanal and nonanal (C7-C9) was both increased in association with the presence of parasites in a density-dependent manner, and found to induce antennal response in Anopheles coluzzi. The production of C7-C9 and other infection-associated compounds via malaria-induced oxidative stress is a suggested mechanism. Malaria remains one of the most important diseases worldwide. As the global strategy for malaria control and elimination evolves, to combat both parasite and vector resistance to drugs and insecticides, the need for innovative tools intensifies. If malaria parasites can alter the human odour profile and attractiveness to mosquitoes, the repercussions would be far reaching: this would likely have a profound influence on the way that malaria spreads through populations, and malaria-specific volatile biomarkers could provide a basis for novel diagnostic tools.