Dr Steve Lindsay and his team at the University of Durham studied 36 pregnant and 36 non-pregnant women living in rural Gambia. Each night three pregnant and three non-pregnant women slept alone under a bednet, in six identical huts. In the morning, the number of mosquitoes collected from each hut was used to estimate the relative attractiveness of each woman. There are several reasons why a pregnant woman might be an attractive meal for a mosquito. Firstly, as her baby grows, a pregnant woman will exhale more rapidly.
Mosquitoes can use many of the chemicals found in human breath to detect a host from a distance.
Secondly, during pregnancy, women become hotter and may release more volatile chemicals attracting mosquitoes from a greater distance. Not only do pregnant women appear to be physiologically more attractive to mosquitoes, but changes in their behaviour may also make them more vulnerable to bites, since the researchers found that expectant women left the protection of their bednet during the night twice as frequently as non-pregnant women. This may be as simple as recommending that women use bednets that have been treated with insecticide and that they check for lurking mosquitoes inside the net when they go to bed. The next challenge for the team will be to develop strategies to reduce the appeal of pregnant women. Ultimately this could lead to more effective repellents which block the most telling odours.