Studies of Malaria Immunity in Moshi, Tanzania

For this Consortial Project 2 study the Joint Malaria Programme, Kilimanjaro Christian Medical Centre contributed samples from individuals in 24 villages in northeastern Tanzania.

The site stretches across a range of altitudes from the slopes of Mount Kilimanjaro to the coastal plain of Tanga (circled on map). The area knows two rainy seasons, a short one (October/November) and a long one (March-July). Malaria transmission is highest in both highland and lowland areas during and following the long rainy season.

The around 8500 unique samples contributed to CP2 come from two cross-sectional surveys, one conducted in the short rainy season of 2001, and one during the long rainy season of 2002. Of special interest in this study is the finding that malaria transmission is strongly associated with altitude (being lower at high altitude, EIR range 0-500+ ib/p/year). By examining the gene frequencies in individuals resident at different altitudes further genes associated with malaria may be identified.

Description of Study Population

The study population comprises four principal ethnic groups, Wapare (37%), Wasambaa (40%), Wachaga (14%) and Wabondei (8%). Some other ethnic groups, such as Masai, are also present but in very small numbers.

Children (0-15) make up for two thirds of the study population, of which half were under 5 years old.

Morbidity and Infection Density

Infection with malaria parasites (Plasmodium falciparum, or other) was determined by inspection of blood smears on slides. Asexual (blood stage) forms of the parasites were counted and parasite density recorded relative to the number of white blood cells in the same sample.

Clinical Information

Clinical information, namely temperature and haemoglobin level, were recorded for all individuals in this survey. History of illness and drug use are also known. Of the 1380 infected individuals 318 (23%) were symptomatic.