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Epidemiological studies have demonstrated the susceptibility of the owl monkey (Aotus trivirgatus) to hepatitis A virus, but have not shown an association between infection and histopathological or chemical evidence of liver disease. Therefore, 12 seronegative, colony-bred monkeys were inoculated intravenously with a fecal suspension containing either PA33 strain hepatitis A virus (a strain recovered from a naturally infected Aotus sp.) or HM-175 virus (recovered from a human). Viral antigen was detected by radioimmunoassay in the feces of six monkeys 6 to 17 days after inoculation with PA33 virus, and by 9 to 21 days serum aminotransferase activities were significantly elevated in each. Antibody to the virus developed in each monkey by 28 days after inoculation. Similar findings were noted in five of six monkeys inoculated with HM-175 virus, although the incubation period preceding aminotransferase elevations was somewhat longer (25 to 39 days). Liver biopsies obtained from the 11 infected monkeys demonstrated mild to moderate portal inflammation, as well as random areas of focal necrosis and inflammation extending outward from the portal region. These data confirm the susceptibility of Aotus sp. to hepatitis A virus and indicate that the infection of this primate provides a useful animal model of human hepatitis A.

Cell culture-adapted HM-175 (Australia) and PA-21 (Panama) strains of hepatitis A virus were compared in a cross-neutralization radioimmunofocus inhibition assay. The ratio of antibody titers achieved with two sera against the two viruses differed by less than twofold, indicating a high degree of antigenic relatedness between epidemiologically disparate strains of virus.

Significant levels of antibodies indicative of a variety of zoonotic infections were demonstrated in sera collected from 64 U.S. military scout and tracker dogs after service in the Republic of Vietnam (RVN). Scrub typhus antibodies were found in 45% of the specimens, melioidosis in 19%, group B arbovirus in 49%, and leptospirosis in 62%. Only 38% of the seropositive reactions for leptospirosis could be related to overseas infections. Tests were conducted on paired sera obtained from 32 of the dogs before service in RVN. Significant increases in titer were demonstrated with scrub typhus, melioidosis, leptospirosis, plague, group B arbovirus, and Rickettsia canada antigens. After 2 to 6 months of service in RVN, 8 of 19 dogs developed antibody titers to at least one of four zoonotic diseases. Only 3 of 45 dogs with 7 or more months of service failed to develop antibodies to one or more of the agents. The serological findings pose questions on the potential epidemiological importance and veterinary significance of scrub typhus, group B arbovirus, leptospirosis, and melioidosis infections in dogs.

Four antigenically related transmissible agents were recovered from canine fecal specimens. The agents produced cytopathic effects in a continuous dog cell line developed in this laboratory. Increased antibody titers were demonstrated in three of the four dogs which provided the isolates. The virus did not produce cytopathic effects in primary canine kidney or thymus cell cultures, or in cell cultures of human, simian, porcine, bovine, feline, and murine origin. The agent is resistant to ether, chloroform, and heat treatment, and the growth of the virus is inhibited by 5-iodo-2-deoxyuridine. After acridine orange staining, green fluorescent intranuclear inclusions are seen in infected cell cultures. By electron microscopy, the virions measure approximately 20 to 21 nm in overall diameter and are present in the nuclei of infected cells. These properties are consistent with membership in the parvovirus or picodnavirus group. The agent hemagglutinates rhesus red blood cells at 5 C and by hemagglutination-inhibition tests could be readily distinguished from H-1, rat virus, and the minute virus of mice. Canine gamma globulin contains high titers of neutralizing antibody and neutralizing antibody was found in a high percentage of military dogs and in beagles of a breeding colony.