West Nile virus is transmitted by a bite from an infected mosquito, in Central Europe mainly by the native common mosquito. The virus occurs naturally in over 300 bird species, and the gnats ingest the virus when they bite a bird. In Europe, seasonal outbreaks are reported each year from southern, eastern, and western European countries. In Austria, a total of 55 domestically acquired West Nile virus cases have been confirmed between 2010 and 2022. The likely sites of infection are in Vienna, Lower Austria, and Burgenland.
Above-average summer temperatures are considered one of the factors directly influencing the spread of West Nile virus in Europe: High temperatures in July, sufficient water areas in June, and the occurrence of West Nile virus in previous years may be associated with new cases.
Horses have a higher risk of infection than humans; therefore, clinical disease usually occurs earlier in horses in an affected area. Both humans and horses can become ill but cannot transmit the virus to other mosquitoes. Thus, the virus cannot be transmitted from horse to horse, nor from horse to human.