West Nile Virus Epidemic in Germany Triggered by Epizootic Emergence, 2019.

Viruses. 2020 Apr 15;12(4).
West Nile Virus Epidemic in Germany Triggered by Epizootic Emergence, 2019.

Ziegler U1,2, Santos PD3, Groschup MH1,2, Hattendorf C4, Eiden M1, Höper D3, Eisermann P4, Keller M1, Michel F1, Klopfleisch R5, Müller K6, Werner D7, Kampen H8, Beer M3, Frank C9, Lachmann R9, Tews BA8, Wylezich C3, Rinder M10, Lachmann L11, Grünewald T12, Szentiks CA13, Sieg M14, Schmidt-Chanasit J4,15, Cadar D4, Lühken R4,15.

Author information:
1. Friedrich-Loeffler-Institut, Federal Research Institute for Animal Health, Institute of Novel and Emerging Infectious Diseases, 17493 Greifswald-Insel Riems, Germany. et al.

Abstract

One year after the first autochthonous transmission of West Nile virus (WNV) to birds and horses in Germany, an epizootic emergence of WNV was again observed in 2019. The number of infected birds and horses was considerably higher compared to 2018 (12 birds, two horses), resulting in the observation of the first WNV epidemy in Germany: 76 cases in birds, 36 in horses and five confirmed mosquito-borne, autochthonous human cases. We demonstrated that Germany experienced several WNV introduction events and that strains of a distinct group (Eastern German WNV clade), which was introduced to Germany as a single introduction event, dominated mosquito, birds, horse and human-related virus variants in 2018 and 2019. Virus strains in this clade are characterized by a specific-Lys2114Arg mutation, which might lead to an increase in viral fitness. Extraordinary high temperatures in 2018/2019 allowed a low extrinsic incubation period (EIP), which drove the epizootic emergence and, in the end, most likely triggered the 2019 epidemic. Spatiotemporal EIP values correlated with the geographical WNV incidence. This study highlights the risk of a further spread in Germany in the next years with additional human WNV infections. Thus, surveillance of birds is essential to provide an early epidemic warning and thus, initiate targeted control measures.