West Nile virus (WNV) is a mosquito-borne viral pathogen of global importance and is currently the most widespread flavivirus. WNV persists in an enzootic transmission cycle between ornithophilic mosquitoes (Culex pipiens spp.) and certain avian species. Species such as crows, Eurasian jays and birds of prey are highly susceptible to a WNV infection and can develop severe clinical signs including fatal encephalitis. By contrast, other avian species may only undergo a subclinical infection. Humans and horses are incidental hosts (i.e., “dead-end-hosts”) where an infection with WNV can range from a mild flu-like illness (i.e., “West Nile fever”) to a severe brain inflammation with fatal outcome.
WNV was detected in Germany (predominantly Eastern Germany) for the first time in 2018 with a total of 12 cases in birds and 2 cases in horses. An infection with WNV is a notifiable disease, for which to date no national control regulations exist. It is, therefore, essential that all animal health measures are based on the EU Animal Health Law.
In Europe, three WNV-vaccines have been approved for horses through the European Medicines Agency. For all three vaccines, the following applies (see recommendations of the StIKo Vet from the 22/10/2018): horses can become infected with WNV despite vaccination yet the vaccination protects them from clinical manifestation and significantly reduces the extent and duration of viremia.
To date no human vaccine has been licensed for WNV yet.
To evaluate the risks WNV and Usutu virus pose for human and veterinary health the Institute of Novel and Emerging Infectious Diseases (INEID) of the FLI conducts a wild bird monitoring program. Together with external partners, blood samples and bird carcasses of wild and captive avian species as well as zoo birds are tested for various arboviruses. This nationwide, unique wild bird monitoring program is supported by numerous sample collectors, including honorary ornithologists as well as members of the veterinary state investigation offices, avian clinics of the veterinary medicine faculties, the Bernhard Nocht Institute for Tropical Medicine (BNITM), the German Mosquito Control Association (KABS), the Nature and Biodiversity Conservation Union (NABU), several avian clinics/practices and bird sanctuaries. Since 2007, more than 8,000 wild bird blood samples have been examined. Before 2018, there was however no evidence for autochthon WNV infections in the tested birds. The same was true for the examined bird carcasses, which were consistently negative for WNV until August 2018.
For 2019, the National Reference Laboratory for West Nile Virus infections already detected the first official case at the beginning of July, followed by more than 100 cases by the end of the year. It can, therefore, be assumed that WNV has been able to successfully overwinter in native mosquitoes in Germany. In autumn 2019, the virus was also detected for the first time in mosquitoes of the Culex pipiens complex as well as being the cause of five human autochthon infections (see RKI: Epidemiological Bulletin 25/2020).
In 2020, the first case of WNV already occurred in the middle of July. Until the end of the year, 64 WNV detections were identified in zoo and wild birds and 22 infected horses were detected, all with more or less severe clinical signs. The majority of cases in birds and horses were confirmed in the already known affected regions of Eastern Germany (federal states of SN, ST, BB, BE). For the first time in the federal state of Thuringia, WNV infection was also detected in diseased and/or dead zoo and wild birds, and a tendency to spread to other districts of Brandenburg was observed. Furthermore, the spread to the federal state of Lower Saxony, district of Helmstedt (one horse with neurological symptoms), was identified. This demonstrated a spreading tendency of WNV compared to 2019. Also, in 2020, WNV was detected in mosquito populations in the affected areas and a significant increase in human disease cases was recorded (see RKI: Epidemiological Bulletin 36/2020 und 37/2020).
For the assessment of WNV infections in sick birds and horses please adhere to the guidelines for sending in sample material according to the Official Collection of Methods (see: Amtliche Methode und Falldefinition, in German language only) and please refer to the appropriate research facility as determined by your state agency (associated state
investigation office). Suspicious samples will subsequently be sent from the state investigation office for further investigation to the national reference laboratory of the FLI.