Biting-density and microfilariae infection of Simulium damnosum complex around the Mada River, Nasarawa State, Nigeria

Abstract

Blackflies (Simulium damnosum sl), are the vectors of Onchocerca volvulus. They breed in fast-flowing, well oxygenated and nutrient containing rivers and streams. Investigations on the biting-density and microfilariae infection rate of S. damnosumsl population caught around the Mada River was conducted between May 2013 to April 2014. Captured flies were morphologically identified and dissected for parity and infectivity rate. A total of 308 adult female S. damnosum sl were caught, 83 died and 225 were dissected. 38  (16.9%) of the dissected flies were parous while the remaining 187 (83.1%) were  nulliparous. 4 (10.5%) of the parous flies were infected with different stages of the parasite. Two of the infected flies harboured head L3 (infective) stage of O. volvulus. The monthly biting-rate (MBR) ranged from 30 (in June) to 2,550 (in September).The calculated transmission potential (number of infective bites per person per month) was recorded in the months of September (62) and October (15). These were the months in which infective flies were caught. These findings indicate low vector’s biting activities and risk of river blindness infection in the study-area. The public health implications of these results in the ongoing Community Directed Treatment with Ivermectin (CDTI) and elimination strategy of river blindness in the state are discussed.

Keywords: infectivity rate, parous flies, multiparous.