Surveillance of West Nile fever in horses in the Czech Republic from 2011 to 2013

Study aim: The West Nile virus (WNV) is an important mosquito-borne flavivirus occurring around the world. Occasionally found in Central Europe, the virus spread massively through whole Hungary between 2008 and 2009. The aim of our study was to determine the recent prevalence of the WNV infection in horses in the Czech Republic. Material and methods: Overall, 2349 serum samples, collected from healthy unvaccinated adult horses in the Czech Republic between 2011 and 2013, were tested. A commercially available competitive ELISA kit (cELISA) was used for this purpose and positive samples were confirmed by virus neutralisation tests using WNV and tick-borne encephalitis virus (TBEV). Results: Altogether 271 of 2348 samples (11.5%) were positive by cELISA. Confirmatory VNT revealed 16 WNV positive samples, 11 of which had titres from 8 to 1024; VNTs with TBEV were negative. Three samples had antibodies against both viruses and the WNV antibody titres were less than or equal to the TBEV antibody titres. A cross reactivity of flaviviruses might have had an impact on the results, but samples with similar WNV and TBEV titres, co-infection with both pathogens cannot be ruled out either. VNT antibody titres in two horses were inconclusive (cut-off titre 4). The place of birth and transfers (if any) were checked for each WNV seropositive horse. Five WNV positive/TBEV negative samples (0.2 %) came from five administrative regions (South Bohemian, Karlovy Vary, Central Bohemian, South Moravian, and Moravian-Silesian) and the respective animals were never moved to a foreign country. Four of these horses never left the farm. Other six WNV positive/TBEV negative horses were imported to the Czech Republic from North America or Central and West Europe and therefore, it is not possible to tell unambiguously whether their infection is autochthonous or imported. Conclusion: The results of the present study confirm that WNV antibodies occur sporadically in horses in the Czech Republic. WNV was found to circulate in different parts of the Czech Republic and not only in the South of Moravia.