Key result
Usutu virus detected in harbor seals, marking the first known fatal mammalian infection.
Why the study?
Usutu virus is distributed throughout Germany with a broad range of suspected accidental hosts, but few reports document the progression of USUV-associated disease.
Case Report (n=42)
No
This report documents the first fatal cases of Usutu virus in mammals, highlighting the importance of including USUV as a potential diagnosis for neurological impairments in marine mammals.
USUV may cause fatal encephalitis in harbor seals; extends known host range to mammals but remains hypothesis-generating.
The zoonotic Orthoflavivirus Usutu virus (USUV) is distributed throughout Germany, putting hosts at a considerable risk of infection nationwide. Besides birds as reservoir hosts, a broad range of accidental hosts is suspected. However, there are few reports documenting the progression of USUV-associated disease. This case report describes the course of fatal USUV infections in three harbor seals (Phoca vitulina) from a rescue center on the North Sea coast in Germany. Corresponding samples were analyzed using (histo-)pathological, immunohistochemical, molecular and phylogenetic methods. The most prevalent findings in clinically affected animals were neurological signs and non-suppurative encephalitis. All animals were found dead or had been euthanized due to animal welfare reasons within 30 h after the onset of clinical signs. Blood samples taken from another 37 young harbor seals from the same rescue center in the same year revealed two further asymptomatic USUV RNA and antibody-positive animals. The sequences were found to belong to USUV lineages Europe 2 and Africa 3, which are known to circulate in birds in Germany. This case report highlights the importance of USUV as a potential diagnosis for neurological impairments in marine mammals and documents the first cases of USUV infection in harbor seals.
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Schwarzer et al. (2026) conducted a case report in Usutu virus (USUV) infection / Neurological signs (n=42). Usutu virus (USUV) exposure was evaluated on Detection of Usutu virus (USUV) RNA and associated pathological lesions. Usutu virus was detected in 3 of 5 harbor seals with fatal neurological signs and non-suppurative encephalitis, marking the first report of fatal USUV infection in mammals.
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