Pregnant women are twice as attractive to malaria carrying mosquitoes as non-pregnant women, according to new research. This added attractiveness is thought to be linked to physiological and behavioural changes and places pregnant women at greater risk of malaria, an important cause of stillbirths, low birth weight, and early infant mortality.
For the research, 36 pregnant and 36 non-pregnant women were studied in the Gambia. Every night during the study, three women from each group slept alone under a bed net in six identical huts. The following morning the number of mosquitoes from each hut was counted to measure the relative attractiveness of each woman, and it was found that that twice as many mosquitoes had been attracted to the pregnant women.
The researchers, who report their findings in the Lancet (2000;355:1972), say that this increased attractiveness is likely to be linked to at least two physiological factors. Firstly, they found that women at an advanced stage of pregnancy exhaled 21% greater volume than non-pregnant women. Mosquitoes are attracted to the moisture and carbon dioxide in exhaled breath.
Secondly, they observed that the abdomens of pregnant women were 0.7°C hotter. They suggest that the hotter, pregnant women released more volatile substances from their skin surface, allowing the mosquitoes to detect them more easily. The fact that the pregnant women left their tents during the night, probably to urinate, twice as often as the non-pregnant group might also be important.
Dr Steve Lindsay of Durham University, one of the study's authors, said: “This study underlines the importance of protection, particularly for women in their first pregnancy. Simple measures can help, such as using bed nets treated with insecticide and checking for lurking mosquitoes inside the net.”
He added: “Our next challenge is to develop strategies to reduce the mosquito attractiveness of pregnant women. We are already looking into the use of bactericidal soap to reduce the chemical signals produced by skin bacteria, which help mosquitoes find blood.”
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R PETERS/INSIGHT
Promoters dressed up as mosquitoes in a Shanghai shopping mall warn Chinese women about malaria