Abstract: In order to explore the pathological characters and pathogenesis of PRRSV variant strain, the microstructure and ultramicrostructure of lung, spleen, kidney and lymph node of piglets infected with PRRSV were studied. The results showed that the major pathological characters of PRRSV variant strain were interstitial pneumonia and adenolymphitis, accompanied by the degeneration and necrosis of liver, spleen, kidney, heart, stomach and intestine. Alveolar macrophages, lymph nodes and lymphocytes and plasma cells in spleen were infected with different degrees, where a large number of viral inclusion bodies were found. The results indicated that the tissue tropism of PRRSV variant strain, compared with the typical strain ch-1a in China, showed great changes and the infection could cause systemic immunosuppression．

Key words: Porcine reproductive and respiratory syndrome virus(PRRSV), variant strain, pathology