Studies on the transmission and prevalence of Bancroftian filariasis in four coastal villages of Tanzania

In surveys of Bancroftian filariasis in four coastal villages in Tanzania, microfilaria rates varied between 28·3 and 15·6% and hydrocoele rates in males over 20 years between 78–5 and 61–3%.Quantitative studies on the intensity of transmission were conducted over a period of 17 months. The estimated potential infective bites per person per year varied from 24 to 189. The number of infective bites was related to filarial endemicity.The vectors in order of importance were Anopheles gambiae s.l., Culex pipiens quinquefasciatus and An. funestus. In all villages An. gambiae s.l. played a role in transmission and in two it was the main vector. Of the total estimated bites by members of the gambiae complex, 16 223 (91·1%) occurred during or following the ‘long rains’ (April to early June). In contrast, transmission by C. p. quinquefasciatus occurred throughout the year. In one village in which C. p. quinquefasciatus was the predominant vector, the biting density of this species was 22 times greater than the biting density of An. gambiae s.l.The level of the microfilaria reservoir in the human population and the density of the vectors were important factors influencing the intensity of transmission.