Usutu virus is a mosquito-borne flavivirus that kills blackbirds and other songbirds across Europe. Human risk is low, but the virus is watched in the same programmes that track West Nile virus.
What Usutu virus is and where it came from
Usutu virus is a flavivirus carried by mosquitoes. Researchers first isolated it in 1959 from a Culex neavei mosquito caught near the Usutu River in Swaziland, according to Vilibic-Cavlek and colleagues in Pathogens on 26 August 2020. Retrospective analysis of archived tissue from a bird die-off showed that the virus emerged in Europe in 1996 in the Tuscany region of Italy, five years before the widely recognised Austrian outbreak of 2001. By 2018 infections had been recorded in sixteen European countries, among them Austria, Belgium, Croatia, the Czech Republic, France, Germany, Greece, Hungary, Italy, the Netherlands, Poland, Serbia, Slovakia, Spain, Switzerland and the United Kingdom. The same review describes severe disease in several bird species in Europe, especially blackbirds and great grey owls, while no bird deaths were reported in Africa.
How the virus moves between birds and mosquitoes
The virus passes between birds and mosquitoes in a cycle that mainly involves Culex species. The Scottish Government page, published on 1 July 2026, names Culex mosquitoes as the vector and describes birds as the primary hosts. Culex pipiens is the main vector, and the Pathogens review adds Aedes albopictus and Aedes japonicus as implicated species, with natural infection of Aedes japonicus documented in Austria. Mammals including people do not pass the virus on. The Scottish Government page explains that viraemia in an infected mammal does not reach high enough levels to infect a biting mosquito. That single fact shapes the whole public health picture: infected people are not a source of onward spread to mosquitoes, so human cases do not seed new local transmission cycles.
Why blackbirds and other songbirds are at risk
Usutu virus is highly pathogenic for several bird species in Europe. The Pathogens review singles out blackbirds and great grey owls, and notes that bird mortality was not reported in Africa, so the European pattern looks different from the African one. The Animal and Plant Health Agency, in a science blog post dated 1 December 2020, reports that the virus can cause a lethal disease in certain species of birds, particularly the common or Eurasian blackbird, and that since its introduction into northern Europe it has caused a reduction in song birds in Germany, Belgium and the Netherlands. The Scottish Government page records that in 2025 the virus was found for the first time in Scotland, in two blackbirds in Ayrshire. The same agency adds that blackbirds and other passerines act as the primary hosts, which is why local bird deaths often signal virus activity before any human case appears.
The signs to look for in a sick or dead bird
Bird disease is often the first visible signal that the virus is active in an area. The Scottish Government page lists the signs to look for: lack of flight response, poor coordination, and neurological problems such as head tremors, a twisted neck and drooping wings. In the United Kingdom, members of the public are asked to report dead birds through the gov.uk Report Dead Birds service or by calling Defra. The Animal and Plant Health Agency has run surveillance for mosquito-borne viruses in wild birds across Great Britain for more than fifteen years, and the 2020 detection in Greater London came out of that long-running monitoring. Reporting a dead bird is therefore a practical contribution to a national early warning system.
What the human case record actually shows
Human Usutu virus infection is uncommon and mostly mild, but neuroinvasive cases exist. The Pathogens review describes neuroinvasive infections in Italy from 2009, three neuroinvasive cases in Zagreb during the 2013 West Nile outbreak and three more in 2018, a French case presenting with facial paralysis in 2016, and a Hungarian case of aseptic meningitis in 2018. Blood donor screening detected Usutu RNA in Austria, including 18 positive donations in 2018, plus single or paired donors in Germany and the Netherlands. The European Centre for Disease Prevention and Control reported 104 human Usutu cases across EU and EEA countries for 2012 to 2021, of which 11 had neurological manifestations. These figures matter because they show that neurological illness from this virus stays rare even where the virus circulates widely among birds.
How Usutu virus is monitored alongside West Nile virus
Usutu virus is not tracked in a separate system. The European Centre for Disease Prevention and Control technical report, published on 14 September 2023, covers surveillance, prevention and control of West Nile virus and Usutu virus infections together across the EU and EEA. For 2012 to 2021 it records 3 632 autochthonous human West Nile cases alongside the 104 human Usutu cases. Sixteen EU and EEA countries reported West Nile virus in humans and animals, while fifteen reported Usutu virus in animal hosts. West Nile virus was found in at least nine mosquito species across thirteen countries, while Usutu virus was detected mainly in birds. Both sit inside One Health surveillance linking public health, animal health and substances of human origin.
What this means for people in Europe
For most people in Europe, Usutu virus is a bird health problem with a low human risk. The Scottish Government page states that the assessed risk of human infection in the United Kingdom is low and that, as of June 2026, no human cases had been reported there despite the virus being present since 2020. The Animal and Plant Health Agency records that a Human Animal Infections Risk Surveillance group assessment also concluded the human risk was low. Diagnosis is complicated because antibodies cross-react with West Nile virus, which is one reason the Pathogens review calls for One Health surveillance. The article does not detail specific mosquito-bite prevention measures beyond general awareness; readers should consult local public-health guidance for personal protection against Culex bites. The public health value lies in watching bird deaths, not in alarm.
Sources
- Epidemiology of Usutu Virus: The European Scenario: Pathogens
- Surveillance, prevention and control of West Nile virus and Usutu virus infections in the EU/EEA: European Centre for Disease Prevention and Control
- Usutu virus: how to report and spot the disease: Scottish Government
- Usutu virus, APHA Science Blog: Animal and Plant Health Agency
This article is general information, not medical advice. Ask a doctor or pharmacist about your own health.