Ovine progressive pneumonia: experimental intrathoracic, intracerebral, and intra-articular infections

Three groups of 4 lambs each were experimentally infected with an isolate of progressive pneumonia virus (PPV) by intracerebral, intra-articular, or intrathoracic routes of inoculation. An additional control group was sham-inoculated by all 3 routes with identically prepared, noninfected inoculum. Sheep were killed 12 to 42 days after inoculation. A mild generalized leptomeningitis was found in 2 of the 4 lambs inoculated intracerebrally. A severe, proliferative synovitis with massive infiltration of lymphocytes and plasma cells was found in the 4 lambs inoculated intraarticularly. Germinal center formation was found in the synovial membrane 42 days after inoculation. Appreciable differences in lung morphologic features were not observed among the 4 groups. The PPV was isolated from virus-inoculated sheep from the choroid plexus, synovium, and lungs from inoculated and noninoculated sites. Nine of the 12 virus-inoculated lambs developed serum antibody to PPV, and specific antibodies were found in the synovial fluid of virus-inoculated joints. Virus was not isolated, lesions were not found, and serum antibody was not demonstrated in sham-inoculated sheep.