Experimental viral hepatitis in the dog: production of persistent disease in partially immune animals.

Experimental infection with canine hepatitis virus has been studied in a series of 49 dogs. The pattern of response to infection was distinctly modified by the immune status of the animal. All of 19 fully susceptible dogs had an acute, fulminating fatal hepatitis when infected with a standard dose of virus, and all of 19 dogs with high levels of immunity to the virus survived without apparent illness. However, 11 dogs were spontaneously encountered with partial immunity to the infectious agent, and these animals developed different, prolonged forms of hepatitis following infection. In four animals death occurred in 8-21 days following what may be called a subacute course. The remaining seven dogs survived up to 8 months with evidence of chronic hepatic damage. The subacute and chronic forms of hepatitis were reproduced experimentally in seven of eight fully susceptible dogs which were passively immunized against the canine hepatitis virus by administration of hyperimmune serum. Although the virus could be found in sites of hepatic damage in the early stages of the subacute and chronic diseases, it could not be demonstrated in the later stages which were characterized by persistent hepatic damage and a marked chronic inflammatory reaction. Dogs with chronic hepatitis eventually developed extensive hepatic fibrosis. The pathologic, physiologic, virologic, and immunologic features of these experimental forms of viral hepatitis are described.