Evaluation of Onchocerca volvulus infectivity status of black flies in post-ivermectin regime in Kachia, Kaduna State, Nigeria

Abstract

The infectivity status of Simulium species is an important factor in assessing the transmission of Onchocerca species. In this study, we determined the biting rate and presence of the larval stage of the parasite to determine the status of onchocerciasis in the post-ivermectin era in the study area. A total of 1.063 black flies were collected in September and October 2023. Dissection was carried out under a microscope to examine the internal organs for the presence of microfilaria and record their condition. The findings indicated that parous flies 311(29.3%) were markedly less prevalent compared to nulliparous flies 752(70.7%). Among the dissected flies, a total of 14 (1.3%) were found to be infected with Onchocerca species. The flies exhibited a bimodal biting pattern, with a peak in the morning occurring between 9 and 10 am and afternoon between 4:00 and 5:00 pm. The monthly biting rates of 5177.0 and 5807.3 in September and October respectively exceeded the World Health Organization's threshold of 1,000 bites per person per month. It is essential to investigate the potential resurgence of onchocerciasis in the study area, which may be attributed to the overlapping presence of cattle, Simulium vectors, and humans.