Malariometric update for the rainforest and savanna of Ashanti region, Ghana.

The epidemiological features of human infection with Plasmodium were studied in a community-based survey of 35 villages in the Ashanti region of Ghana. The overall prevalences of malarial parasitaemia in subjects aged > or = 2 years were 50.72% in forest areas and 49.72% in savanna. Plasmodium falciparum was the predominant species everywhere, followed by P. malariae in the savanna and P. ovale in the forest. The highest prevalence of asexual parasitaemia (of any species) occurred in the youngest age-group (2-9 years). The geometric mean intensities of parasitaemia among the parasitaemic (i.e. the parasite density indices) were 557, 640 and 452 parasites/microliter for P. falciparum, P. ovale and P. malariae, respectively. For each Plasmodium species encountered, the mean intensity of parasitaemia decreased with age. Mixed infections were observed in 24% and 30% of the parasitaemic subjects from the forest and savanna, respectively. Those infected with P. falciparum were more likely to carry P. ovale (odds ratio = 2.02) or P. malariae (odds ratio = 2.63) than those who were not infected with P. falciparum. Mean intensities of the parasitaemias in mixed infections were substantially higher than the sums of those in the corresponding single infections. When comparing villages, parasite density indices were found to be correlated with the prevalences of parasitaemia (r = 0.56).