Maternal malaria and gravidity interact to modify infant susceptibility to malaria

Every year at least 30 million women in malaria-endemic areas of Africa become pregnant. Many of them develop placental malaria, a pregnancy-specific form of the disease, which frequently results in low birth weight of the child.

Placental malaria might increase the susceptibility of infants to malaria, but previous studies were inconclusive. A careful study by Patrick Duffy and colleagues (of the Seattle Biomedical Institute), published in the international open-access medical journal PLoS Medicine, found that placental malaria does raise the risk of malaria in infants. The researchers also discovered a surprising protective effect against malaria in first-time mothers, regardless of whether they had placental malaria.

Duffy and colleagues studied a total of 453 infants, of which 69 were born to mothers with placental malaria. Of those 69, 31 were born to first-time mothers, and 38 to mothers who had given birth before. They then followed those infants for a year and checked whether during that time they became sick with malaria. There were two major findings. First, the researchers found that overall children whose mothers had placental malaria were more likely to get sick with the disease themselves. Second, they found something surprising about the birth order of the infants, namely that children from first time mothers were less likely to develop malaria, regardless of whether their mother had placental malaria.

These results suggest that both the number of previous pregnancies and placental malaria affect an infant's chances of developing malaria. It might be that in first-time mothers placental malaria stimulates the mother's immune system and this somehow protects the baby against malaria. These provocative results will prompt further studies of the effects of malaria during pregnancy. If confirmed, the results here suggest that reducing placental malaria specifically in women who had previously given birth would have the most effect.

http://www.plosmedicine.org/