Transmission dynamics of Simulium damnosum in rural communities of Akwa Ibom State, Nigeria.

BACKGROUND & OBJECTIVES Onchocerciasis is endemic in some parts of Akwa Ibom State, Nigeria. This study describes the entomological parameters of transmission in three rural communities of Akwa Ibom State, prior to ivermectin intervention in 2004. METHODS Blackflies were caught using human bait and 90% of the flies were dissected for parity. All parous flies were further dissected for the presence of filaria larvae. Monthly and annual biting rate, and transmission potential were calculated using standard methods. RESULTS A total of 4296 adult Simulium damnosum were caught on human bait, 4119 were dissected of which 208 (5.1%) were infected with Onchocerca volvulus larvae. Transmission parameters varied significantly (p < 0.05) in the three villages. Annual biting rates, ranged from 9490 to 11,218 bites per person per year. The annual transmission potential ranged from 131 to 189 infective larvae per person per year, monthly biting rate and monthly transmission potential varied significantly (p < 0.05) in the three villages. Transmission was highly seasonal occurring during the peak of rainy season from August to October. There was no transmission during the dry periods--November to March, and the early rainy periods--April to May. The diurnal biting activity of the fly exhibited a bimodal pattern with a morning peak (0900-1000 hrs) and a more marked evening peak (1600-1700 hrs). INTERPRETATION & CONCLUSION The results indicate that there is a temporal and spatial variation in the transmission dynamics of S. damnosum in the study area.