On September 21, 2018, the first case of West Nile virus infection in a horse was detected in Germany. Confirmatory testing was performed by the National Reference Laboratory for West Nile Virus Infections (WNV) in birds and horses of the FLI. The affected animal comes from the district Elbe-Elster (Brandenburg).
Like humans and birds, horses can become infected by virus-bearing blood-sucking mosquitoes. Like humans, horses are considered as so-called “dead end hosts”, i.e. the virus does not replicate sufficiently to permit retransmission of the infection to other mosquitoes. Therefore, WNV-infected and diseased horses do not represent an infection risk.
Similarly to humans, the majority of WNV-infected horses do not develop any clinical symptoms. However, some animals show distinct central nervous disorders due to WNV-induced meningitis or encephalitis. Febrile general illness, in contrast, is rare. Central nervous disorders include stumbling, paraplegia, ataxia, general weakness, tremor, and partial or complete paralysis. Clinically diseased horses may survive WNV infection; however, up to 20 percent of the affected animals show irreversible neurological damage. In 22 to 44 percent of clinically diseased horses the outcome is fatal.
There is no specific therapy for WNV infection, the disease can only be treated symptomatically. Three vaccines for prophylactic immunization licensed by the European Medicines Agency (EMA) are available in Germany for application in horses. These include an inactivated whole virus vaccine, a recombinant live vaccine, and a recombinant inactivated vaccine.
WNV infection of birds and horses is a notifiable disease.
In Europe, WNV was first detected in France in the early 1960ties and has since then become established in the entire Mediterranean area. WNV infections of humans and horses occur regularly, mainly in southern and south-eastern countries (France, Italy, Croatia, Albania, Greece, Turkey, Austria, Hungary, Serbia, Spain, Czech Republic).
Considering the epidemiological situation, the occurrence of WNV in Germany is not surprising. So far, one hawk from Bad Düben (Saxony), two great grey owls from Poing (Bavaria), one great grey owl from Halle and one hawk from Bernburg (both Saxony-Anhalt), and two snowy owls and one common blackbird from Berlin have among others been tested positive for WNV. Hot weather conditions over a long period of time favor virus replication in mosquitoes. Therefore, further cases of WNV in birds and horses cannot be excluded.
The National Reference Laboratory of the FLI has carried out extensive monitoring studies in horses and birds for many years without any evidence of WNV infections. The recent WNV cases were detected in cooperation with the Bernhard-Nocht-Institute in Hamburg in the frame of wild bird monitoring. Currently, investigations on the presence of WNV in mosquitoes in the area of Halle and Poing are carried out in cooperation with the Leibniz Centre for Agricultural Landscape Research (ZALF).