High seroprevelance of west nile virus antibodies observed in horses from southwestern Nigeria.

To investigate exposure of Nigerian horses to West Nile virus (WNV), we determined the seroprevalence rate of anti-WNV antibody in a cohort of 145 horses. Serum samples were collected from three locations in southwestern Nigeria between October, 2011, and July, 2012. The horses were asymptomatic and unvaccinated against WNV at the time of sampling. All sera were tested using a competition enzyme-linked immmunosorbent assay (ELISA) and by an immunoglobulin M (IgM)-specific ELISA. High rates of anti-WNV antibody prevalence were observed in all locations with a mean level of 90.3% (95% confidence interval 84.3-94.6%). None of the horses had detectable anti-WNV IgM. This is the first ELISA-based report of WNV seroprevalence in Nigerian horses and suggests that WNV is enzootic in the study areas, indicating a potential risk of infection in humans and animals.