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Presentations at the 49th Annual Meeting of the American Society of Tropical Medicine and Hygiene, Houston, Texas, Oct/Nov 2000
By Michele Barry, MD
Synopsis: A short review of the current literature concerning pregnancy and malaria was presented at a Meet the Professor session in Houston, Texas, last fall. Three articles published during the past year were discussed in detail.
Sources: Lindsey S, et al. Effect of pregnancy on exposure to malaria mosquitoes. Lancet 2000;355:1972; Diagne N, et al. Increased susceptibility to malaria during the early postpartum period. N Engl J Med 2000;343:598-603; Nosten F, et al. Effects of plasmodium vivax malaria in pregnancy. Lancet 1999;354:546-549.
The first article described an interesting study, comparing the relative attractiveness of pregnant and nonpregnant women to mosquitoes in rural Gambia. Each night, three pregnant and nonpregnant women slept alone under a bed-net in six identical huts. They were given malaria chemoprophylaxis, and in the morning the total numbers of collected mosquitoes from each hut were enumerated. The procedure was carried out with the same group of women for three consecutive nights and was repeated with 12 different groups of women. Twice as many Anopheles gambiae mosquitoes—the main malaria vector in Gambia—were attracted to pregnant women (mean 6.3 per night 95% confidence interval [CI] 4.5-8.7) than to their nonpregnant counterparts (mean 3.1 per night 95% CI 2.1-4.5; P =0.0002). Lindsey and colleagues postulate three mechanisms by which pregnant women might be more attractive to these vectors: 1) increased CO2 release due to increased respiratory rate during pregnancy; 2) increased blood flow to peripheral skin causing release of attractive volatile substances; and 3) Pregnant women tended to leave their nets for urination at night twice as frequently as nonpregnant women, offering more movement as a mosquito attractant.
Pregnancy is associated with increased susceptibility to malaria. It is generally agreed that this increased risk ends with delivery; persistence of susceptibility during puerperium has never been investigated. Diagne and colleagues described a study of 71 pregnancies in 38 women in a malaria endemic area within Senegal, from the year before conception to the year after delivery. They note an increased incidence of malaria during the second and third trimesters. Of great interest, the susceptibility to malaria continued until 60 days after delivery, perhaps supporting the view that depression of components of immunity is a key factor involved in malaria in pregnant women (akin to "galloping consumption" seen in the postpartum woman with tuberculosis.) Diagne et al suggest malaria chemoprophylaxis for pregnant women should be continued for at least two months after delivery.
The last subject reviewed was a prospective study of pregnant Karen women living in camps for displaced people on the western border of Thailand. Effects of P. vivax on anemia and pregnancy outcome were compared with those of P. falciparum. As with P. falciparum, P. vivax malaria during pregnancy was more common among primigravidas and was associated with anemia and increased risk of low birth weight. Unlike P. falciparum, P. vivax malaria was not associated with miscarriage, stillbirth, or shortened duration of pregnancy. Although the degree of anemia and low birth weights were not as severe as those seen in P. falciparum-infected pregnant women, Nosten and associates still felt P. vivax chemoprophylaxis during pregnancy was justified.