The changed pattern of malaria endemicity and transmission at Amani in the eastern Usambara mountains, north-eastern Tanzania

Parasitological and entomological studies on malaria were conducted between 1980 and 1982 on the Amani hills in the eastern Usambara mountains of north-eastern Tanzania. Malaria vectors were scarce on the Amani hills until the late 1960s and it was generally presumed that any cases of malaria transmission must have been contracted by people while visiting lower altitudes where malaria is holoendemic. However, the malaria vectors Anopheles funestus and An. gambiae have both become more abundant during the 1970s and 1980s and sporozoite-positive specimens of both have been found. Malaria asexual parasite rates have been shown to have increased, for instance from 52.7% in 1980 to 53.8% and 63.7% in 1981 and 1982, respectively. The percentage of parasitized children aged below 1 year whose parents report that they have not visited lowland localities away from the Amani hills has increased, from 71.4% in 1980 to 80.0% and 91.0% in 1981 and 1982, respectively, suggesting possible local malaria acquisition. These parameters have been confirmed by increasing sporozoite rates from 0.0% in 1967-1971 to 0.09% in May-June 1973 and 11.1% in August and December 1980. Various factors including climatological changes and increased agricultural activities are attributable to this changed malaria endemicity and transmission.