Abstract
Usutu virus (USUV) is a zoonotic arbovirus causing avian mass mortalities. The first outbreak in North-Western Germany occurred in 2018. This retrospective analysis focused on combining virological and pathological findings in birds and immunohistochemistry. 25 common blackbirds, one great grey owl, and one kingfisher collected from 2011 to 2018 and positive for USUV by qRT-PCR were investigated. Macroscopically, most USUV infected birds showed splenomegaly and hepatomegaly. Histopathological lesions included necrosis and lymphohistiocytic inflammation within spleen, Bursa fabricii, liver, heart, brain, lung and intestine. Immunohistochemistry revealed USUV antigen positive cells in heart, spleen, pancreas, lung, brain, proventriculus/gizzard, Bursa fabricii, kidney, intestine, skeletal muscle, and liver. Analysis of viral genome allocated the virus to Europe 3 or Africa 2 lineage. This study investigated whether immunohistochemical detection of double-stranded ribonucleic acid (dsRNA) serves as an alternative tool to detect viral intermediates. Tissue samples of six animals with confirmed USUV infection by qRT-PCR but lacking viral antigen in liver and spleen, were further examined immunohistochemically. Two animals exhibited a positive signal for dsRNA. This could indicate either an early state of infection without sufficient formation of virus translation products, occurrence of another concurrent virus infection or endogenous dsRNA not related to infectious pathogens and should be investigated in more detail in future studies.
Highlights
In summer of 2018, a mass mortality of common blackbirds (Turdus merula) was observed in Germany, for which Usutu virus (USUV) was identified as the causative a gent[1]
While relatively low numbers of lethal USUV cases have been reported in birds in South-West Germany between 2011 and 2 0144,10, fatal cases occurred in great grey owls in a zoological garden in Berlin with introduction of a new USUV lineage in 201511
Fever and rash have been observed in patients[3] and life-threatening meningoencephalitis and peripheral nerve paralysis occur in a low number of humans, highlighting USUV as a potential threat to human h ealth[32,36,37,38,39]
Summary
In summer of 2018, a mass mortality of common blackbirds (Turdus merula) was observed in Germany, for which Usutu virus (USUV) was identified as the causative a gent[1]. This mosquito-borne flavivirus belongs to the Japanese encephalitis virus serogroup and is closely related to West Nile virus (WNV) and Japanese encephalitis virus (JEV). Fever and rash have been observed in patients[3] and life-threatening meningoencephalitis and peripheral nerve paralysis occur in a low number of humans, highlighting USUV as a potential threat to human h ealth[32,36,37,38,39]. This underlines the importance of arbovirus surveillance programs and the need for more precise descriptions of pathological lesions and pathogenesis
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