The West Nile virus (WNV) is one of the most significant zoonotic, vector-borne pathogens in Europe. This virus is mainly transmitted by native mosquitoes of the Culex genus. As part of the OH SURVector project, a uniform Austria-wide monitoring programme for WNV and other pathogens in mosquitoes was carried out in 2025. Traps were set up twice a month from May to October at 69 locations. The captured individuals were identified and tested for the presence of WNV. A total of 6,146 mosquitoes were caught, most of which belonged to the species Cx. pipiens/torrentium, the most important vector of WNV in Europe. The mosquitoes were grouped into 1,313 pools and analysed. No WNV or other pathogen was detected in any of these pools.

In 2025, significantly fewer mosquitoes were caught compared to the previous year, 2024. The weather in the summer of 2025 – with warm, dry and sunny June and August, but a relatively cool, wet and cloudy July – was unfavourable for the development of many mosquito species and is reflected both in the seasonal trend in catch numbers and in the overall low abundance. The pronounced drought that characterised a significant part of the growing season further reduced the availability of suitable breeding waters and contributed significantly to the reduction in populations. Another key factor in the low mosquito population was the very low occurrence of floodwater mosquitoes (e.g. Aedes vexans, Ae. sticticus). As there were no significant flooding events, the floodwater breeding sites necessary for these species were not available, which reduced their occurrence accordingly. The partner countries of the OH SURVector project, in which mosquito monitoring programmes are carried out (Czechia, Slovakia, Hungary), also describe 2025 as a year with a very low mosquito population.