The risk of onchocerciasis infection by human population movements between high and low transmission settings in Ghana

Background Onchocerciasis control strategies have focused on mass drug administration (MDA) to reduce morbidity in high-risk (HR) areas (sites close to blackfly breeding sites). However, with the current drive towards elimination, treatment must be extended to low-risk (LR) areas. It is uncertain how well HR and LR communities are connected for decision making in recommending treatment strategies to include the LR areas. We provided data on current onchocerciasis infection status, connectivity between HR and LR communities and rates of human movement within some endemic communities in Ghana. Methods Selected communities were 5km (HR) and 15km (LR) from breeding sites. Questionnaires were administered to obtain data on demographics and human movement patterns. Samples were collected from participants and tested for O. volvulus infections using Ov16 RDT and presence of microfilariae (mf) in skin snips using microscopy and quantitative PCR. Results We observed a significantly higher onchocerciasis prevalence in HR than LR sites for both sero-prevalence (42.5% vrs 16.0%) and mf prevalence (15.2% vrs 4.1%) [P<0.0001]. There was a high connectivity between the HR and LR with about 64–82% people who moved from HR to LR and 3.2-10% from LR to HR daily or weekly. Infection levels in those who moved from HR to LR communities were higher than those who moved from LR to HR, although these were not statistically significant (P>0.05). Some individuals in Lancha (a LR community) who tested positive for infection frequently visited the HR communities for farming. Conclusions A strong connectivity existed between HR and LR communities by human movement. On the average >60% of participants moved between endemic communities (between HR and LR) either daily, within the week or weekly. This supports the need to initiate treatment in LR areas; hence, such movement data would be useful during assessment of onchocerciasis elimination and delineation of transmission zones.