Number of known West Nile virus infections on the rise

At least 26 people in Germany have been infected with West Nile virus this year as a result of being bitten by a native mosquito. In 13 cases, according to the Robert Koch Institute (RKI), the infections were detected in blood donors who did not show any symptoms of the disease. Four of the infected persons fell seriously ill. In 2023, 7 West Nile infections transmitted by domestic mosquitoes were reported to the RKI and 17 infections in the previous year.

Most infections were recorded for Saxony (7), Saxony-Anhalt (6) and Berlin (5). There were also reports from Brandenburg (3), Schleswig-Holstein (2) and one each from Thuringia, Lower Saxony and North Rhine-Westphalia, although the person from NRW is believed to have been infected in Hamburg, according to the RKI.

High number of unreported cases

In general, there is a very high number of unreported cases of West Nile virus, as an infection is asymptomatic in around 80% of cases. According to the RKI, almost 20 percent have mild, unspecific symptoms such as fever or skin rash - these also often go unnoticed.

More severe and fatal courses of West Nile fever usually affect older people with pre-existing conditions. Only around one percent of infections lead to such severe neuroinvasive diseases.

Blood donors are increasingly tested

In the first years in which the virus was detected in this country, blood donors were not tested as extensively as they are now, according to the RKI's assessment of the reporting figures. Higher case numbers in later years were partly due to increased testing

According to the RKI, the virus is mainly transmitted by mosquitoes between wild birds. Mosquitoes infected by birds can transmit the virus to humans and other mammals. The Culex mosquitoes, which are widespread throughout Germany, are therefore considered the main vectors.

In late summer 2019, according to the RKI, the first West Nile virus infections transmitted by domestic mosquitoes were reported in eastern Germany (5 in total). In the following years, infections were also reported in the summer and fall months in eastern Germany (Berlin, Brandenburg, Saxony-Anhalt, Saxony and Thuringia). Experts assume that the number of cases will increase as a result of climate change.