HAIRS risk assessment: Usutu virus
Qualitative assessment of the risk that Usutu virus presents to the UK population.
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In Europe, Usutu virus (USUV), a mosquito-borne flavivirus, was first recognised in Austria in wild birds in 2001, and subsequently its range expanded across the European Region.
In August 2020, the first USUV infected wild birds in the UK were identified. Since then, genomic sequencing has revealed several USUV detections in birds and mosquitoes across South East England to be genetically similar suggesting that USUV has persisted in the UK regardless of new introductions of the virus. The detection of USUV in overwintering mosquitoes provides further evidence of the integration of USUV into the natural enzootic cycle within the UK’s natural temperate conditions. As of September 2025, no human cases of USUV have been reported in the UK.
This risk assessment provides a qualitative description of the current risk to the UK human population, highlights gaps in evidence and provides recommendations for mitigating the public health risk.
Updates to this page
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Updated the report to reflect the latest Usutu virus epidemiology in Europe, ongoing mosquito surveillance in the UK and detections of Usutu virus in wild and captive birds in the UK since 2020.
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Updated risk assessment.
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First published.