Parasite diversity in adult patients with cerebral malaria: a hospital-based, case-control study.

Thirty adult patients with cerebral malaria (CM) were recruited for this study. Two clinical groups were used as controls: those with mild malaria (n = 20) and asymptomatic volunteers (n = 20). Thick and thin blood smears were examined for detection of Plasmodium falciparum and estimating infection intensity. A nested polymerase chain reaction (PCR) using allele-specific primers for merozoite surface protein gene was used to determine the parasite diversity of Plasmodium falciparum causing CM. Plasmodium falciparum was detected in blood smears of all malaria patients. No significant difference in parasite count was found between the groups. Thirteen (65%) of the asymptomatic volunteers had a positive PCR for P. falciparum. Multiple alleles were found in 17 (58.6%) patients with CM, but only in 7 (35.6%) with uncomplicated malaria. Multiple alleles were also found in 6 (46.2%) of the 13 PCR-positive asymptomatic individuals. We could not identify a specific strain or strains of P. falciparum that showed a significant association with disease severity. Therefore, we assume that the development of CM in adults residing in endemic areas is more dependent on strain multiplicity rather than on a specific strain or strains of P. falciparum, and that the parasite intensity has no relationship with disease severity. Asymptomatic adults may repeatedly be exposed to low levels of a wide range of different strains during low transmission season and acquire sub-patent parasitemia. This may also confer premunition that renders them relatively resistant to CM.