Granulomatosis of lymphoid tissue in post-weaning multisystemic wasting syndrome in pigs during epidemic and endemic phases.

Post-weaning multisystemic wasting syndrome (PMWS) is causally associated with infection of pigs by Porcine Circovirus type 2 (PCV2). Lesions in lymphoid tissues of 52 PMWS-positive pigs sampled years 1998-2000 (epidemic) were compared with lesions from 127 PMWS-positive pigs sampled 2006-2008 (endemic). A variable degree of lymphoid depletion was a constant feature in tissues with microgranulomas formed by a scant number of centrofollicular epithelioid cells, or granulomas clustered in multiple undelimited nodules with little tendency to confluence, formed by epithelioid macrophages and a few multinucleate giant cells. Granulomatosis of lymphoid tissues is known in PMWS of pigs due to type IV hypersensitivity. Granulomatosis of lymphoid tissues was apparent in 1.07% during the 1998-2000 period and in 12.42% in the more recent period. Results suggest that frequency of lymphoid granulomatosis is influenced by the epidemiology of the disease.