Coinfection by porcine circoviruses and porcine parvovirus in pigs with naturally acquired postweaning multisystemic wasting syndrome

Postweaning multisystemic wasting syndrome (PMWS) is an emerging disease in swine. Recently, the disease has been reproduced with inocula containing a newly described porcine circovirus (PCV), designated PCV 2, and porcine pa rvovirus (PPV). In order to determine if these viruses interact in naturall y acquired PMWS, affected tissues from field cases were examined by immunoh istochemistry (IHC) and polymerase chain reaction (PCR) for PCV 2 and PPV, as well as by PCR for the other recognized porcine circovirus, PCV 1. Porci ne circovirus 2 was detected by PCR or IHC in affected fixed or frozen tiss ues from 69 of 69 cases of PMWS collected over 3 years from 25 farms. Porci ne parvovirus was detected in 12 of the same cases, and PCV 1 was detected in 9 of 69; however, an apparent decrease was found in the sensitivity of t he PCRs used to detect the latter 2 viruses when fixed tissue from the same cases were compared with the use of frozen tissues. Porcine circovirus 2 w as not detected by PCR in affected tissues from 16 age-matched pigs that ha d Streptococcus suis-associated disease. Electron microscopic examination o f plasma pooled from 15 pigs with PMWS revealed the presence of PCV and PPV , whereas these viruses were not observed in pooled plasma from 5 age-match ed clinically normal pigs. These results confirm and extend previous findin gs documenting a consistent association of PCV 2 with PMWS. As well, infect ion by PPV or PCV 1 or both may be an important cofactor in the pathogenesi s of some, but apparently not all, cases of PMWS.