The importance of body odour in malaria

The chances of being bitten by a mosquito are related to genes that control body odour, according to a recent study.

In a study involving pairs of identical and non-identical twins, each twin placed a hand at an end of a Y-shaped wind tunnel as air was pumped through to carry their body odour. Swarms of mosquitoes were released and moved towards or away from each twin’s hand. For identical twins there was an even distribution of mosquitoes in both sections, but results for non-identical twins were more varied. Authors of the study, published in Plos One, concluded that the mosquitoes were attracted to a genetically linked body odour.

Mosquitoes infected with the malaria parasite are even more sensitive to human body odour, probably because the parasite enhances the insects’ sense of smell. Researchers demonstrated this effect by placing malaria mosquitoes (Anopheles gambiae) infected with the Plasmodium falciparum parasite into a container containing nylon stockings that had been worn by volunteers for 20 hours. Infected mosquitoes were three times more likely to be attracted to the smelly stockings than uninfected insects.

The importance of body odour has been demonstrated at other stages of the malarial parasite’s life cycle too. Scientists have observed changes in the body odour of infected mice that could serve to attract mosquitoes.

They found that the scent of infected mice was not completely different, but levels of compounds already present were altered. This was particularly noticeable in mice that were still infectious but showed no symptoms – corresponding to an important phase in the parasite’s life cycle. Mosquitoes were particularly attracted to the mice when the parasites were at the gametocyte stage, which is when they need to be ingested back into a mosquito in order to reproduce.

Researchers believe that the parasite may manipulate its host’s scent to ensure its continued survival. Work is now under way to investigate whether a similar pattern of odour change occurs in humans.

According to the latest World Health Organization estimates, there were 198 million cases of malaria worldwide in 2013 and the disease led to 584,000 deaths, representing a decrease in incidence and mortality rates of 30 per cent and 47 per cent, respectively, since 2000. The burden is heaviest in Africa, where an estimated 90 per cent of all malaria deaths occur. Children aged under five account for 78% of all deaths.

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Citation
The Pharmaceutical Journal, May 2015;Online:DOI:10.1211/PJ.2015.20068512