Circovirus-like viral associated disease in weaned pigs in Indiana

Inclusion bodies with staining affinity and ultrastructural characteristics typical of circoviruses that stained positive for porcine circovirus (PCV) -like virus were demonstrated in association with granulomatous lesions in multiple tissues of three clinically ill 10- to 12-week-old pigs. A syndrom e of poor growth and wasting in 5-15% of weaned pigs was an intermittent pr oblem on a 450-sow one-site farrow-to-finish swine farm in Indiana. Routine diagnostic testing did not demonstrate a cause. Gross examination of three representative weaned pigs from two farrowing groups over a I-month period revealed generalized lymphadenopathy and interstitial pneumonia. A unique microscopic finding for all three pigs was granulomatous inflammation of ly mphoid tissues associated with large numbers of multinucleate giant cells a nd characteristic viral inclusions in the cytoplasm of macrophages. These i nclusions were round, homogeneous, and magenta to basophilic, varied in siz e (5-25 mu m), and either were single or formed botryoid clusters. Ultrastr ucturally, these inclusions were composed of electron-dense paracrystalline arrays of small nonenveloped icosahedral viral particles that were approxi mately 17 nm in diameter. The sizes and shapes of the virus particles, the unique microscopic appearance of the inclusions, and the positive staining of the intracytoplasmic viral inclusions by the Feulgen technique are consi stent with circoviruses. Immunohistochemistry for PCV-like virus demonstrat ed viral antigen in the cytoplasm of macrophages that were within inflammat ory infiltrates in a variety of organs. The described inclusion bodies stai ned positively.