Experimental transmission of porcine circovirus type 2 (PCV2) in weaned pigs: a sequential study

Weaned specific pathogen-free pigs were inoculated intranasally with porcin e circovirus type 2 (PCV2) and killed in groups of two or three animals at 6, 13, 20, 27 and 34 days post-inoculation (dpi), together with appropriate uninfected controls, for examination by histopathological, immunohistochem ical (immunogold silver staining; IGSS), polymerase chain reaction (PCR) an d viral isolation techniques. Serum samples were also collected for detecti on of antibodies. No major clinical signs were observed in infected pigs, a nd gross lesions were essentially limited to the lungs and lymph nodes of s ome of the animals. Histologically, no lesions were seen at 6 dpi, but bron chointerstitial pneumonia was invariably noted from 13 dpi onwards. Granulo matous inflammation, with or without intracytoplasmic inclusions, was prese nt in lymphoid tissues (e.g., lymph nodes, thymus, spleen and tonsil) from day 20 onwards, being most severe at days 20 and 27 dpi. Liver inflammation was present at days 13, 20 and 27 dpi. Virus was demonstrated in the tissu es by isolation and PCR methods throughout the experiment. PCV2 antigens we re detected by IGSS in bronchial and bronchiolar epithelial cells, in monon uclear cells and multinucleated giant cells within inflammatory lesions, an d in mononuclear cells of apparently normal tissues (e.g., lamina propria o f the small intestine and the bronchus-associated lymphoid tissue). The les ions were consistent with those of postweaning multisystemic wasting syndro me (PMWS), although not all previously reported PMWS lesions were seen. PCV 2 antibodies were detected in infected pigs from day 13 onwards. The result s demonstrated widespread distribution of PCV2 after infection and persiste nce of the virus in vivo for at least 34 days. It would appear that PCV2 ca n induce PMWS lesions in weaned pigs in the absence of porcine parvovirus a nd other common swine pathogens. (C) 2000 Harcourt Publishers Ltd.