Diversity of Plasmodium falciparum populations and complexity of infections in relation to transmission intensity and host age: a study from the Usambara Mountains, Tanzania

Diversity and complexity of infections with Plasmodium falciparum were desc ribed from cross-sectional surveys in November-December 1996 in 6 villages in the Usambara Mountains, Tanzania, where transmission ranged markedly fro m 0.03 to 91 infective bites per individual per year. Ferry-eight samples, stratified for age and parasite densities, were examined from each village (n = 288). Genotyping was performed by a nested PCR method using primers sp ecific for allele families of genes for the merozoite surface protein 1 (ms p-1) and merozoite surface protein 2 (msp-2). A high degree of genetic dive rsity was found within each village but there were no differences found amo ng the 6 villages. Poisson regressions showed significant effects of host a ge, village and interaction between host age and village on the complexity of infection. There was a positive, non-linear relationship between complex ity of infection and transmission intensity with a maximal number of genoty pes found per individual even at high transmission intensities. Furthermore there was a significantly lower complexity found in adults (> 15 years) as compared to children (< 15 years) in the lowland village. This difference was not found as transmission intensity decreased. By comparing data from t he same geographical area, using the same methods, and taking into account confounding factors, the present study provides evidence for an effect of b oth age and transmission intensity on complexity of infection with P. falci parum.