Porcine circovirus type 2 (PCV2) is often associated with subclinical infections and swine post weaning multisystemic wasting syndrome (PMWS). In the present study, 28-day-old piglets were inoculated with PCV2, porcine reproductive and respiratory syndrome virus (PRRSV), as well as PCV2+PRRSV. Macroscopic lesions, histologic lesions, virus distribution in tissues were systematically examined. Histologic lesions were found in both single PCV2 and dual PCV2+PRRSV-inoculated piglets, including lymphoid depletion and intracytoplasmic inclusion bodies within histiocytes, as well as bronchointerstitial pneumonia and granulomatous inflammation in the lungs. The lesions were more severe in piglets inoculated with PCV2+PRRSV than in those with PCV2. PRRSV-inoculated piglets showed lymphoid depletion and moderate interstitial pneumonia, but no inclusion body or granulomatous inflammation. PCV2 antigen intensity in many tissues was higher in the coinfection group than in the single PCV2, but PRRSV antigen intensity had no difference between the PRRSV and PCV2+PRRSV groups. Therefore, PCV2, not PRRSV, induced the inclusion bodies and granulomatous inflammation that characterizes PMWS. PRRSV+PCV2 coinfection also promoted the replication of PCV2, but not of PRRSV.

Key words: Coinfection, Histologic lesions, Immunohistochemistry, PCV2, PRRSV