Possible impact of Urbanization on the breeding of Blackfly Vector and transmission of Onchocerciasis in some parts of Nigeria

Abstract

Onchocerciasis, caused by Onchocerca volvulus is transmitted in Nigeria by female blackflies of the Simulium damnosum group. To monitor interruption of transmission and or elimination of onchocerciasis, traps are normally set and or human landing collection of female flies carried out at high risk areas along these river banks (the breeding sites). Currently, the protocol demands that at least 6000 female flies be collected from each transmission zone for Polymerase Chain Reaction (PCR) analysis in order to determine the infectivity rate of the female blackflies. During the May 2021 Nigerian Onchocerciasis Elimination Committee (NOEC) Meeting, it was observed that very low or no female S. damnosum flies were trapped and or caught in 18 months of field exercise from the river systems in Kebbi and Zamfara States as well as Abuja the Federal Capital Territory (FCT). These river systems hitherto were  productive breeding sites of blackfly vector hence transmission of onchocerciasis was active and the areas were endemic for onchocerciasis. Again, these rivers are known to traverse the semi-urban and urban centres in these areas. It was suggested that among other factors, that rapid urbanization in these areas may be a major contributory factor that has affected the ecology of the breeding sites and has made the rivers currently considered non-suitable breeding waters for the blackfly vectors. This study was a literature search undertaken to bring to focus the possibility that urbanization may have negatively impacted on the breeding of Simulium vectors and transmission of onchocerciasis in Kebbi and Zamfara States as well as Abuja, the Federal Capital Territory, and helped the elimination of the disease. Some research questions are also thrown up to guide empirical and operational studies.