Longitudinal Study of the Occurrence of Usutu Virus and West Nile Virus Infections in Birds in a Zoological Garden in Northern Germany

Usutu virus (USUV) and West Nile virus (WNV) are known to cause diseases and mortalities in bird populations. Since 2010/2011, USUV has circulated in Germany and spread nationwide, while WNV was only introduced into East Germany in 2018. The zoological garden investigated is located in Northern Germany, where USUV infections in wild birds have been detected for several years. In this longitudinal study conducted over a four-year period, zoo birds were sampled biannually and screened for molecular and serological evidence of USUV and WNV. USUV genomes were detected in eight of the sampled birds and whole-genome sequences revealed the circulation of USUV lineages Europe 3 and Africa 3. Of the eight birds infected with USUV during the study period, four died after the infection, while four survived without displaying clinical signs. Furthermore, in a few of the birds, a USUV (re-)infection was confirmed on a serological level with three birds producing USUV-neutralizing antibodies (nAbs) over a period of four years. Nonetheless, in two birds sampled throughout this longitudinal study, neither a USUV nor a WNV infection was evident. In 2022, WNV nAbs were detected for the first time in a juvenile zoo bird, indicating the introduction of the virus into this region.