Pathology and distribution of viral antigen in birds naturally infected by West Nile virus lineage 2.

West Nile virus (WNV) is one of the most widely distributed zoonotic arthropod-borne viruses in the world and has been identified as the cause of potentially fatal disease in birds. While the pathomorphology and virus distribution in birds are well documented for WNV lineage 1 (WNV-1) epizootics in North America, few (histo-)pathological and immunohistochemical studies are available for Europe, where WNV lineage 2 (WNV-2) is co-circulating with WNV-1.WNV-2 infected dead birds were evaluated (histo-)pathologically at the German regional veterinary laboratories and academic pathological institutes. Immunohistochemical labelling (IHC) with an in-house rabbit anti-WNV polyclonal antibody (OM8) and subsequent evaluation of IHC signal distribution were performed at the National Reference Laboratory.In total, tissues of 54 birds from 32 different species including first-time descriptions in endangered avian taxa were analysed. Gross and histopathological findings aligned well with previous reports of avian WNV disease and the heart was once more confirmed as a reliable target organ for diagnostics. However, the frequent identification of WNV antigen (Ag) in enteric ganglial neurons and glial cells in several bird species as well as signs of prolonged disease duration in corvids contrasted with earlier findings on the North American continent.In conclusion, this study broadens the range of avian taxa, for which information on pathomorphology and distribution of viral Ag associated with fatal WNV disease is available, and will facilitate diagnostics in the field. Furthermore, some of the described findings differed from the available literature suggesting deviations in the pathogenesis of locally circulating WNV-2 strains.