| Summary: | In 2015, over 850,000 people died from chronic hepatitis and hepatocellular carcinoma (HCC) caused by hepatitis B virus (HBV). A novel hepatitis B-like virus has recently been identified in domestic cats. The pathogenic potential of domestic cat hepadnavirus (DCH), for which 6.5% to 10.8% of pet cats are viremic, is unknown. We evaluated stored formalin-fixed, paraffin-embedded biopsies of diseased and normal feline liver for the presence of DCH using PCR and in situ hybridization (ISH). DCH was detected in 43% (6/14) of chronic hepatitis cases and 28% (8/29) of HCCs, whereas cholangitis (<i>n</i> = 6), biliary carcinoma (<i>n</i> = 18) and normal liver (<i>n</i> = 15) all tested negative for DCH. Furthermore, in DCH-associated cases, the histologic features of inflammation and neoplasia, and the viral distribution on ISH were strikingly similar to those seen with HBV-associated disease. Several histological features common in human HBV-associated hepatitis, including piecemeal necrosis and apoptotic bodies, were identified in DCH-positive cases of chronic hepatitis. In two cases of HCC examined, the proliferation index in regions that were ISH-positive was higher than in ISH-negative regions. The intracellular distribution of virus in both hepatitis and HCC demonstrated that viral nucleic acid is present in both nuclear and cytoplasmic forms. Collectively, these findings demonstrate a compelling association between DCH and some cases of chronic hepatitis and hepatocellular carcinoma in the cat that mirrors features of HBV-associated hepatopathies. Future investigations of viral epidemiology and natural history are needed to establish the impact of DCH on feline health.
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