Hourly biting activity of blackflies (Diptera: Simulidae) and transmission of Onchocerciasis in the Imo River Basin, Nigeria

Abstract The study, carried out in the Okigwe endemic area in Nigeria, elucidated the longitudinal indices of onchocerciasis transmission. In all, 6,517 female S. damnosum s.l. were caught between September, 2005 and August, 2006. The abundance was more in the dry season, during higher temperatures, when windy, when many people worked on the farm at the same time, when there were on-going activities that disturbed the vegetation including clearing of bushes. The annual biting rate (ABR) was 23,204 bites per person per year. The monthly biting rates ranged from 47 to 5,677 bites per person per month in August 2006 and January 2006 respectively. The circadian biting activity showed a primary peak at between 10.00 and 11.00 hours and a secondary peak between 15.00 and 17.00 hours. There was a bimodal peak Infective biting; the first between 8.00 and 11.00 hours, and the second between 15.00 and 18.00 hours. The annual biting rate (ABR) was 23,504 bites per person per year. The annual transmission potential (ATP) was 663 infective bites per person per year. There was intense and sustained on-going transmission of onchocerciasis in the Upper Imo River Basin. These results inform the need for renewed definite action towards its mitigation.