A Field-Based Assessing the Role of PCV-2 and Other Swine Viruses in Postweaning Multisystemic Wasting Syndrome

A case-control study was conducted to assess the association of major swine viral pathogens, including porcine circovirus type 2 (PCV2) with postweaning multisystemic wasting syndrome (PMWS). Cases were defined as individual pigs with a clinical history of progressive weight loss and respiratory signs and that were subsequently diagnosed with PMWS on the basis of characteristic histopathological lesions. Controls were pigs clinically unaffected and/or from herds in which PMWS had not been diagnosed and with no clinical signs compatible with PMWS. A total of 31 cases and 56 controls were identified from diagnostic submissions or farms within a 6-month period. Among viruses examined, PCV2 appeared to be the most strongly associated with PMWS (P\u3c.05). Risk for PWMS was much higher if animal was coinfected with porcine reproductive and respiratory syndrome virus (odd ratio =31.2). However, PCV2 was found in 62.5% of the control animals and was not detected in 2 of the 31 PMWS pigs. Furthermore, no significant genetic difference was observed among PCV2 isolates from PMWS and clinically normal pigs. The role of PCV2 in PMWS remains to be reassessed

Experimental Reproduction of Severe Disease in CD/CD Pigs Coinfected with PRRSV and Type 2 Porcine Circovirus

Postweaning multisystemic wasting syndrome (PMWS) has been recognized worldwide and is characterized clinically by wasting, dyspnea, and occasionally by icterus in nursery and grow-finish pigs. Type 2 porcine circovirus (PCV2) is consistently demonstrated in PMWS lesions. At the Iowa State University Veterinary Diagnostic Laboratory, both porcine reproductive and respiratory syndrome virus (PRRSV) and PCV2 are detected in tissues from most cases of PMWS. Since PRRSV-PCV2 coinfection has also been associated with “atypical PRRS” hepatitis, 3 week old cesarean-derived, colostrum-deprived (CD/CD) pigs were inoculated with PRRSV, PCV2, both PRRSV and PCV2, or uninfected cell culture media in order to compare the independent and combined effects of these agents. PRRSV-inoculated pigs developed respiratory distress and interstitial pneumonia typical of that previously reported for this agent. None of the pigs in the PRRSV or control groups became moribund or developed hepatitis. PCV2-inoculated pigs developed lymphoid depletion and sporadic hepatitis associated with 40% mortality. Pigs in the PRRSV/PCV2 group developed severe and persistent pyrexia and dyspnea; mortality between 10 and 20 days was \u3e90% and was associated with severe interstitial pneumonia and/or hepatitis. We conclude that 1) PCV2 alone can induce clinical disease and lesions of PMWS in CD/CD pigs, 2) PCV2 alone does not induce significant respiratory disease in CD/CD pigs, 3) PCV2/PRRSV coinfection induces more severe clinical disease and lesions of PMWS than PCV2 alone, including severe interstitial pneumonia, and 4) PCV2 coinfection is responsible for the hepatitis associated with cases of “atypical PRRS.” Simultaneous coinfection of PRRSV and PCV2 has the potential to significantly exacerbate morbidity and mortality. The timing of exposure and decay of maternal antibody to PCV2 and other pathogens may play a critical role in determining whether PCV2 infection induces PMWS or remains subclinical