Bancroftian filariasis in an irrigation project community in southern Ghana

An epidemiological study to document the endemicity and transmission charac teristics of bancroftian filariasis was conducted in an irrigation project cummunity in southern Ghana. In a 50% random sample of the population, the prevalence of microfilaraemia was 26.4% and the geometric mean microfilaria l intensity among positives was 819 microfilariae/ml of blood. Hydrocoele w as found in 13.8% of the males aged greater than or equal to 18 years, and 1.4% of the residents examined, all females, had lymphoedema/elephantiasis. Detailed monitoring of the microfilarial intensity in 8 individuals over a 24-h period confirmed its nocturnal periodicity with a peak at approximate ly 0100 hours. The most important vector was Anopheles gambiae s.l., follow ed by An. funestus. The abundance of these mosquitoes and their relative im portance as vectors varied considerably between the wet and the dry season. Opening of the irrigation canals late in the dry season resulted in a rema rkable increase in the population of An. gambiae (8.3% of which carried inf ective filarial larvae) to levels comparable to those seen during the wet s eason, suggesting that the irrigation project is responsible for increased transmission of lymphatic filariasis in the community.