Seasonal Variations in Biting Density and Infectivity of Simulium damnosum Complex in Ezeagu and Oji-River Local Government Areas of Enugu State, Nigeria

Background and Objectives: Onchocerciasis is a parasitic filarial disease of the tropics, having serious effects on global public health and the economy of endemic countries. Nigeria is among the most endemic countries, necessitating much research and control program interests. This study determined the rate of transmission of onchocerciasis in Oji-River and Ezeagu Local Government Areas of Enugu State, Nigeria.

Methodology: Human landing sampling method was used to collect black flies. Parity assessment was conducted to determine the age of fly populations. Parous flies were further dissected to detect the presence or absence of Onchocerca larvae. Biting rates and transmission potentials were calculated using standard methods. The principal vector groups in the study area were identified morphologically.

Results: A total of 352 adult female flies were collected during the study period. These were identified as members of the forest species of the S. damnosum complex. There were significant differences between monthly abundances of black flies caught during the entire study period (P < 0.04). Comparison of the monthly biting rates (MBRs) showed a significant difference in (P < 0.02). The MBR was lowest in February but highest in October. Generally, parity rate of over 50 % was observed throughout the period except for November. None of the flies dissected was infective. Diurnal biting activities of black flies between the months were significantly different from each other (P < 0.01).

Conclusions: Onchocerciasis transmission is low in the studied area, and is largely by means of the forest black flies as these were the only observed group. None of the dissected flies was found to be infective. The findings of this study will be of tremendous benefit to policy makers in the National Onchocerciasis Elimination Programme. It calls for a continuous monitoring of onchocerciasis disease conditions in the study area.