Increasing Seroprevalence In Horses Evidences Widespread Circulation Of West Nile Virus In Albania.

West Nile virus (WNV) is a zoonotic mosquito-borne flavivirus that causes West Nile disease, an emerging and re-emerging infection of major global importance. Horses are an important sentinel species for monitoring WNV circulation. Since viraemia in horses is brief and viral loads in the blood are low, serological assays are the primary tools used to monitor WNV exposure. This study aimed to estimate the seroprevalence of WNV antibodies in horses in Albania. Between 2017 and 2020, 509 serum samples were collected from apparently healthy, unvaccinated horses across different regions of the country. Samples were analysed using two commercial ELISA kits for the detection of total WNV-specific antibodies and WNV-specific IgM. Of the 509 samples tested, 143 (28.1%) were positive for total antibodies, while 12 (2.35%) were IgM-positive, indicating recent infection. As no horse tested positive in both assays, the combined seroprevalence was 30.5% (155/509; 95% CI: 26.6-34.6%), without double counting. A subset of 37 ELISA-positive sera was subsequently tested using the virus neutralisation test (VNT), the gold-standard confirmatory assay for WNV-specific antibodies. The VNT confirmed the presence of WNV-neutralising antibodies in 35/37 (94.6%) samples, with titres ranging from 1:10 to 1:640. These findings indicate widespread WNV circulation in Albania. Compared with previous reports based on samples collected in 2010-2011, seropositivity was higher and evidence of exposure was detected in previously unaffected areas, highlighting the need for continued integrated veterinary and public health surveillance.