Evidence of hepatitis A infection in immature rhesus monkeys.

Forty immature (less than 2 years old) rhesus monkeys (Macaca mulatta) with marked increases in aspartate and alanine aminotransferase activities were examined. Serological and histopathological evaluations were done to determine if affected animals were infected with hepatitis A virus. Although no clinical signs of illness were noted in any of the monkeys, an excellent correlation was found between the increased serum aminotransferase values and seropositivity with the acute phase (IgM) HAVAB-M antibody. Histopathological evaluations of livers of selected animals revealed hepatic lesions consistent with those in chimpanzees and marmosets infected with hepatitis A virus: generalized activation of sinusoidal lining cells, focal hepatocellular necrosis with occasional acidophilic bodies, and cuffs of mononuclear cells in the portal areas. Although no animals were seropositive for HAVAB upon receipt from the breeding colony, a total of ten of 18 animals for which serological data were available had seroconverted to HAVAB positivity during the 4-month observation period. These results are consistent with hepatitis A infection in immature rhesus monkeys and indicate the potential significance of serological testing in animals in which hepatic function is being evaluated.