Pathological and immunohistochemical findings of natural highly pathogenic avian influenza infection in tufted ducks during 2010-2011 outbreaks in Japan.

In the winter of 2010-2011, an outbreak of highly pathogenic avian influenza virus (HPAIV) infection occurred in wild and domestic birds in Japan. Tufted ducks were found dead in an urban area of Toyota City, Koriyama, Fukushima Prefecture. Two tufted ducks were examined histopathologically, immunohistochemically and molecularly. Gross findings included marked dark-red clotted blood in the pectoral muscles and multifocal hemorrhages on the serous membranes. Microscopically, non-suppurative meningoencephalitis, multifocal to coalescing pancreatic necrosis and severe pulmonary congestion were observed. HPAIV antigen was detected in the malacic areas, neuronal, glial and ependymal cells, pulmonary capillary endothelial cells and epithelium of pulmonary bronchioles, necrotic pancreatic acini and degenerated cardiac myocytes. The HPAIV isolate was genetically classified into clade 2.3.2.1 group A. The broad distribution of virus antigen in brain and pulmonary tissues associated with HPAIV spontaneous infection in tufted ducks might be useful in understanding its pathogenesis in nature.