Bancroftian filariasis in the Igwun Basin, Nigeria. An epidemiological, parasitological, and clinical study in relation to the transmission dynamics.

A 12-month field and laboratory study was carried out to determine the epidemiology, clinical features, and transmission dynamics of bancroftian filariasis in the Igwun Basin, Nigeria. A total of 1,418 individuals (768 males, and 650 females) were examined for clinical signs of filariasis. 690 day provocative blood samples (DPS), and 728 night blood samples (NBS) were examined for microfilaremia. 14.3% of males and 11.1% of females were mf positive. 5.8% of DPS, and 19.5% of the NBS were mf positive. An overall microfilaria rate of 12.8% was recorded in the basin. Prevalence and microfilarial density increased with age. The highest average density of 35 mf/20 ml NBS occurred in the 40-59-year-old male individuals. The mean microfilarial density in DPS and NBS were 7.9 and 28.0 per 20 ml blood in males, respectively, and 6.2 and 20.0 per 20 ml DPS and NBS in females, respectively. Disease rates of 55.5% were recorded for males, and 68.1% for females. The clinical signs observed were: Chyluria (9.1% for males, 16.7% for females); hydrocele (15.5%); elephantiasis (15.5% in males, 29.2% in females); and enlarged groin glands (15.5% in males, 22.2% in females). All clinical signs were associated with microfilariae. Anopheles gambiae s.I., and Culex pipiens s.I. were the two mosquito vectors identified. The estimated mean annual biting rates were 5508 and 10448 for A. gambiae s.I. and C. pipiens s.I., respectively. Their respective mean infection rates were 21.7% for A. gambiae s.I. and 22.7% for C. pipiens s.I.; with microfilarial densities of 4.1 and 6.6.(ABSTRACT TRUNCATED AT 250 WORDS)