Biting on human body parts of Simulium vectors and its implication for the manifestation of Onchocerca nodules along Osun River, southwestern Nigeria

Background: The biting preference of Simulium vectors has been known to influence the distribution ofOnchocerca nodules and microfilariae in human body. There is, however, variation in biting pattern of Simuliumflies in different geographical locations. This study investigates the biting pattern on human parts by Simuliumvectors along Osun river system where Simulium soubrense Beffa form has been implicated as the dominantvector and its possible implication on the distribution of Onchocerca nodules on human body along the river.Methods: Flies were collected by consented fly capturers on exposed human parts namely head/neck region,arms, upper limb and lower limb in Osun Eleja and Osun Budepo along Osun river in the wet season (August–September) and the dry season (November–December) in 2008. The residents of the communities were alsoscreened for palpable Onchocerca nodules.Results: The results showed that number of flies collected below the ankle region was significantly higher thanthe number collected on other exposed parts (p <0.05) while the least was collected on head/neck region in bothseasons. The lower trunk was the most common site (60%) for nodule location at Osun Eleja followed by uppertrunk (40%). Nodules were not found in the head and limb regions. At Osun Budepo, the upper trunk was themost common site of the nodule location (53.8%) followed by the lower trunk (38.5%) and head region (7.7%).Conclusion: Though, most of the flies were caught at the ankle region, the biting of other parts coupled with thepresence of nodules at the head and upper trunk regions showed that Simulium vectors could obtain microfilariaefrom any part of the body, thus increasing the risk of onchocerciasis transmission.