Pathobiology of highly pathogenic avian influenza virus (H5N1) infection in mute swans (Cygnus olor)
Résumé
The authors report the results of pathological, virological and PCR examinations carried out on 35 mute swans (Cygnus olor), which succumbed to a highly pathogenic avian influenza virus (H5N1 ) infection during an outbreak in Southern Hungary. The most frequently observed macroscopic lesions included haemorrhages under the epicardium, in the proventricular and duodenal mucosa and pancreas; focal necrosis in the pancreas; myocardial degeneration; acute mucous enteritis; congestion of the spleen and lung and the accumulation of sero-mucinous exsudate in the body cavity. Histopathological lesions comprised lymphocytic meningo-encephalomyelitis accompanied by gliosis and occasional perivascular haemorrhages; multi-focal myocardial necrosis with lympho-histiocytic infiltration; pancreatitis with focal necrosis; acute desquamative mucous enteritis; lung congestion and oedema; oedema of the tracheal mucosa and in young birds, the atrophy of the bursa of Fabricius as a result of lymphocyte depletion and apoptosis. The observed lesions and the moderate to good body conditions were compatible with findings in acute HPAI infections of other bird species reported in the literature. Skin lesions and lesions typical for infections caused by strains of lower pathogenicity (LPAI) like emaciation or fibrinous changes in the reproductive and respiratory organs, sinuses and airsacs were not observed. The H5N1 subtype avian influenza virus was isolated in embryonated fowl eggs from all cases and it was identified by classical and molecular virological methods. These results were confirmed by the analyses carried out at the Veterinary Laboratory Agency, Weybridge.
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