Mosquitoes prefer pregnant women

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Pregnant women are twice as attractive to malaria canting 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
[degrees]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."

Author/s: Roger Dobson
COPYRIGHT British Medical Association

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