Limited Antibodies to Henipaviruses Detected Among Nigerian Horses Using Pseudotyped Virus Neutralization Tests

The Hendra virus (HeV; Henipavirus hendraense) and Nipah virus (NiV; Henipavirus nipahense), members of the genus Henipavirus, are high-consequence pathogens that have caused multiple zoonotic outbreaks with high mortality. Frequently, pigs or horses have acted as bridging hosts between bats, the reservoir hosts, and people. We used pseudotyped viruses with the fusion (F) and glycoprotein (G) envelope proteins of the NiV and Ghana virus (GhV; Henipavirus ghanaense) in neutralization tests (PVNTs) to screen serum samples from 138 apparently healthy horses in northwest Nigeria. No antibodies to GhV were detected in the 138 samples tested. Two serum samples were positive for antibodies to NiV on an initial screen using a single serum dilution, giving a prevalence of 1.45% (95% CI: 0.4-5.13%). Both positive samples were from female, non-local breeds of horses that were used for polo and were 15 and 20 years old. The only significant risk factor found through Chi-squared analysis was the older age category (p = 0.028). On titration in a PVNT, a half-maximal inhibitory concentration was calculated for both samples (IC₅₀ = 11.6 and 16.8). These data suggest the limited exposure of horses to NiV in the sample region but confirms that horses can act as a sentinel population for the circulation of henipaviruses.