Bimodal transmission of cerebral malaria and severe malarial anemia and reciprocal co-existence of sexual and asexual parasitemia in an area of seasonal malaria transmission.

The parasite dynamics in severe malaria (SM) varies with malaria endemicity. This study was conducted in eastern Sudan, an area of seasonal and unstable malaria transmission. From the beginning of October to the end of December (malaria season) in the years 2000, 2001, and 2003, 99 patients with severe malarial anemia (SMA) and 54 patients with cerebral malaria (CM) were identified. There was marked variation in the incidence of SMA and CM (up to six folds) and in the CM/SMA incidence ratio, over 3 years. In the heavy season of 2003, CM peaked at the beginning of the season and declined within a month at a time that the SMA reached the peak. At diagnosis, the rate of gametocytemia had inclined from approximately 10% to 100% from the beginning to the end of the season. During follow-up, gametocytemia was more associated with SMA than with CM. Paradoxically, the late occurring SMA was associated with early gametocytemia (day 7) and the opposite was true in CM. In conclusion, within the season the transmission of CM and SMA was bimodal, the prevalence of the asexual and sexual parasitemia was reciprocal, and the peaks of transmission and gametocytemia were paradoxical.