Observations on Onchocerciasis Transmission in Parts of Middle Imo River Basin, Nigeria after Repeated Treatment with Ivermectin

Abstract

Onchocerciasis is both public health hazard and socio-economic problem despite concerted efforts and high expenditure on control programme. To assist with certification of elimination, cross sectional study was conducted at Ibii and Lolo Rivers, breeding sites of Simuluim damnosum in the Imo River Basin from September 2015 to February 2016. S. damnosum were caught by human bait technique and assessed for parity, infection and infectivity status. Biting rates and transmission potentials were calculated by standard methods. Of the 591 flies caught/dissected, 0.88% (5/591) were infected with sausage (L1) and pre infective stage (L2) but no infective stage (L3). The distribution of O. volvulus at the two sites were insignificant (P>0.05). The diurnal biting activity exhibited a bimodal pattern with morning (9.00am and 10.00am) and evening (4.00pm and 5.00pm) peaks. Monthly biting rates (MBR) of 2,581 and 1877.25 bites / persons/ months were found for Ibii and Lolo Rivers respectively. The monthly transmission potentials (MTP) for the two stations were zero, indicative of extremely low transmission. The public health implications of these findings are discussed in the context of the on going Community Directed Treatment with Ivermectin (CDTI) and elimination strategy of onchocerciasis in the state.