Community views on blackfly control along Nigeria’s Edo–Ondo border

Abstract

Many communities along the Edo-Ondo border in southern Nigeria remain highly endemic for onchocerciasis. Despite more than two decades of mass drug administration (MDA), transmission persists, necessitating the National Onchocerciasis Elimination Committee (NOEC) to designate the zone as special intervention hotspots. Slash-and-Clear (S&C) has emerged as a promising, community-based approach that can be integrated with ongoing MDA campaigns. This study assessed community knowledge of blackfly, onchocerciasis and willingness to sustain S&C without external financial or logistical support.

Structured questionnaire was administered to 79 key informants from Edo (n = 59) and Ondo (n = 20) communities along Ose River. Focus group discussions (FGDs) were conducted pre- and post-intervention (April 2023 and April 2025, respectively) with participants from 76 communities that participated in slash-and-clear. Three communities declined due to security and socio-cultural reasons.

Prior to intervention, all 79 (100%) key informants reported frequent blackfly bites and expressed the need for strategies to reduce the nuisance. FGD findings corroborated this, with participants recognizing blackflies and their biting burden but showing limited awareness of onchocerciasis as a disease. Common protective measures included wearing long clothing and applying chemical substances on skin to prevent bites. At post-intervention, participants collectively reported noticeable decline in blackfly activity, which reinforced community enthusiasm for sustaining the intervention. Although some communities expressed willingness to continue without monetary incentives, the provision of essential tools and materials was consistently emphasized by majority.

The reduction in blackfly nuisance was a motivator for community’s willingness to sustain the intervention. Continued support and routine monitoring by the Edo and Ondo State governments, especially for communities reluctant to participate without financial incentives, are critical to prevent reinfestation in committed areas. This supervision will ensure the broader success of the S&C strategy and the elimination of onchocerciasis in communities along the Edo-Ondo border.

Introduction

Onchocerciasis is one of the neglected tropical diseases and remains a major global public health concern, commonly associated with characteristic onchocercal nodules, severe skin disease (onchodermatitis), lymphatic complications (such as hanging groin), epilepsy in children and impaired vision and blindness [1]. In West Africa, blackflies of the Simulium damnosum complex have been established as the principal vector of onchocerciasis [2,3]. Blackflies breed in fast flowing, highly-oxygenated rivers or streams and their immature stages can be found attached to rocky substrates, submerged and trailing vegetations. The preference for this specific breeding habitats restricts their presence primarily to communities close to viable breeding sites, which in turn shapes the geographical distribution of onchocerciasis [4]. The distribution, intensity, and endemicity levels of onchocerciasis are largely influenced by the ecology and behaviour of the blackfly, particularly the effective flight range, when seeking bloodmeal (appetitive flight driven by the need to find blood), which is unlikely to exceed 15 km from breeding sites [4]. As a result, the most heavily affected communities are almost invariably located within 15 km radius to the breeding site [4]. This breeding site preference and oviposition behaviour of the blackflies influenced the current intervention being deployed to control or eliminate onchocerciasis in this study.