Preeclampsia is thought to be more common in parts of the world where there is a serious malaria problem and it has often been speculated that there might be a connection. Malaria is more common in a first pregnancy and so is preeclampsia. In both cases, the reasons are unknown. Researchers from the USA, UK and Tanzania set out to investigate the possibility that malaria might lead to preeclampsia.
When a pregnant woman has malaria, it can result in a high concentration of malaria parasites developing in the placenta, in which case she is said to have ‘placental malaria’. This is very harmful to the mother and to the fetus; it leads to low birth weight and, in Africa alone, is estimated to be responsible for the deaths of about 200,000 infants every year. A woman who is pregnant for the first time is most likely to suffer from placental malaria, and to have her placenta become highly infected and extremely inflamed. If she later becomes pregnant again, she will be protected to some extent by antibodies she has developed against the parasites in the placenta.
Working with pregnant women in Tanzania, the researchers found that, overall, women with placental malaria were no more likely than other women to develop hypertension. However, for young first-time mothers, having placental malaria increased the risk of hypertension about three-fold. The researchers also measured levels of a substance called sVEGFR1 (sometimes called sFlt1), which is known to increase before and during preeclampsia and is thus considered to be a ‘biomarker’ for the condition. sVEGFR1 levels were high in first-time mothers with either placental malaria or hypertension, or both, but levels were not raised in other mothers with these conditions. A related substance, VEGF, which is known to be involved with the process that causes inflammation, was high in first-time mothers with placental malaria, but not in those who had hypertension alone. sVEGFR1 can bind to VEGF and block its action.
Because sVEGFR1 was produced by the fetus’ cells, and VEGF was produced by the mother’s cells, the scientists concluded that the mother and fetus were in conflict over how to deal with the parasites in the placenta, and that this conflict led to preeclampsia.
The researchers say their findings support the view that, in young first-time mothers only, placental malaria can cause preeclampsia. Action to reduce the chance of such women getting malaria would have the additional benefit of lowering their chance of developing preeclampsia.
Citation: Mutabingwa TK, Bolla MC, Li JL, Domingo GJ, Li X, et al. (2005) Maternal malaria and gravidity interact to modify infant susceptibility to malaria. PLoS Med 3(11): e407.
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