Distribution
In Europe, it was first detected in Austria in 2001. However, a retrospective analysis revealed it in a bird tissue sample collected in 1996 from the Tuscany region of Italy. In Hungary, Usutu virus was first identified in a blackbird in 2005; this deceased bird was found in Budapest’s 11th district. In 2006, Usutu virus–infected blackbird carcasses were also found in Budapest’s 16th and 18th districts.
Affected Host Species
The virus primarily infects birds but can also cause symptoms in mammals and humans. In Europe, it has been detected in 28 wild bird species to date. Taxonomically and ecologically, the virus closely resembles West Nile virus. However, unlike West Nile virus, Usutu virus rarely causes disease in humans, and then primarily in individuals with weakened immune systems. In Hungary, the virus was first detected in human blood in 2018. However, similarly to West Nile virus, all non-avian hosts are considered dead-end hosts, meaning they cannot transmit the virus to others.
Transmission and Vectors
Its vectors are mainly mosquitoes, similar to West Nile virus. Usutu virus has been isolated from numerous mosquito species, with the common house mosquito (Culex pipiens) likely being the most common vector.
Symptoms
Usutu virus infections produce symptoms similar to those of West Nile virus. In birds, the infection manifests as neurological signs, as well as enlargement and inflammation of internal organs (liver, spleen, heart). In humans, most infections are asymptomatic. Some patients may experience general malaise, headache, fever, muscle pain, and occasionally rashes. The disease typically resolves on its own within 1–2 weeks.
Treatment and Prevention
There is no vaccine against Usutu virus. In most cases, the disease resolves spontaneously. There are no reports in the literature of severe complications requiring medical treatment.