While there was intense infection activity in many newly affected districts last year, particularly in Lower Saxony and Schleswig-Holstein, the National Reference Laboratory for West Nile Virus Infections at the FLI has confirmed only four cases in horses and 21 cases in wild and zoo birds this season.
The majority of infections once again occurred in the federal states of Berlin, Brandenburg, Hamburg, Saxony-Anhalt and Saxony, all of which have been affected in recent years. However, three cases in horses in south-west Germany, all of which occurred in close proximity to each other in the Bergstraße and Rhein-Neckar districts, are noteworthy. Attention should be paid to WNV in this area, especially as cases have already occurred in neighbouring districts in previous years.
The significantly lower number of cases in 2025 could be due to unfavourable climatic conditions for mosquitoes this year; the cold, dry spring meant there were significantly fewer mosquitoes than in previous years. Furthermore, last year's wave of infections led many horse owners to follow StIKo Vet's vaccination recommendation [ZU1], meaning that many horses currently have up-to-date protection against WNV. Additionally, a number of zoo and falconry birds in Germany are vaccinated against WNV. Furthermore, the National Reference Laboratory has documented that all horses that have died from WNV in Germany to date were not vaccinated against it.
The virus has become endemic in several regions of Germany, circulating in bird and mosquito populations. It is expected to occur annually and to spread beyond the affected areas. If favourable climatic conditions prevail during the mosquito season — for example, a warm, humid spring followed by a long, hot summer — a sharp increase in cases is highly likely.
The Robert Koch Institute is responsible for providing information on current infection figures in humans.
