Emergence and Spread of Usutu Virus in Central Europe On the Basis of the Outbreak in Switzerland
In late summer 2006 considerable mortality in wild and captive passeriformes and strigiformes was observed around the Zurich Zoo, Switzerland. All animals were found in a range of 2 km.2 Observed clinical signs involved depression, ruffled plumage, incoordination, and dropping to the ground with seizures and death within minutes. At necropsy the nutritional status was generally moderate to poor in wild birds and poor to good in captive animals. Necropsy showed marked splenomegaly, mild hepatomegaly, and pulmonary hyperemia in most animals. Histopathologic lesions were very discrete and consisted mainly of neuronal necrosis, leucocytolysis in and around the brain blood vessels, and miliary liver necrosis. The diagnosis of Usutu virus (USUV) infection was confirmed with immunohistochemistry (IHC) and reverse transcription polymerase chain reaction (RT-PCR). Partial nucleotide sequence comparisons revealed >99% identity between the viruses that emerged in Zurich in 2006, in Vienna in 2001, and in Budapest in 2005. In 2007 significantly lower mortality was observed, but USUV infection was confirmed for the first time beyond Zurich city limits.
Usutu virus is a poorly recognized, mosquito-borne flavivirus, which was first isolated from Culex neavei in South Africa in 1959.6 When USUV emerged for the first time outside Africa, it caused fatalities in warm-blooded hosts such as blackbirds (Turdus merula) and great grey owls (Strix nebulosa) in the region around Vienna between 2001 and 2005.2,4,5 More recent cases have been reported in Italy3 and Hungary1.
The authors thank the keepers at Zurich Zoo and all the laboratory personnel for their help during the study. The work and organization of Ms. G. Hürlimann is gratefully appreciated.
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