Malaria in pregnant Cameroonian women: the effect of age and gravidity on submicroscopic and mixed-species infections and multiple parasite genotypes.

Polymerase chain reaction (PCR)-based methods were used to investigate malaria in pregnant women residing in Yaounde, Cameroon. Microscopy and species-specific PCR-based diagnosis show that at delivery 82.4% of the women were infected with Plasmodium falciparum (27.5% blood-smear positive and 54.9% submicroscopic infections). The prevalence of P. malariae and P. ovale was 7.6% and 2.5%, respectively, with 9.4% infected with more than one species. Based on genotyping of the merozoite surface protein 1 (msp-1) and msp-2 alleles, the mean number of genetically different P. falciparum parasites in peripheral blood was 3.4 (range = 1-9) and 3.5 (range 1-8) in the placenta. Plasmodium falciparum detected by microscopy and PCR as well as mixed-species infections were significantly higher in women < or = 20 years old and paucigravidae, but maternal anemia was associated only with microscopic detection of parasites. Neither submicroscopic infections nor number of parasite genotypes decreased significantly with age or gravidity. Thus, pregnancy-associated immunity helps reduce malaria to submicroscopic levels, but does not reduce the number of circulating parasite genotypes.