Role of porcine circovirus in postweaning multisystemic wasting syndrome

Type 2 PCV showed a higher association with PMWS (OR=9.3, 1.9\u3c95% Cl\u3c45.3) than other viruses. Risk for PWMS was much higher if an animal was co-infected with porcine reproductive and respiratory syndrome virus (OR=3l.2, 4.1\u3c95% Cl\u3c238). However, PCV2 was also found in controls (35/56) 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. Collectively, naïve swine were shown to be susceptible to PCV2. However, the causal role of PCV2 in PMWS could not be conclusively demonstrated. Development of PMWS may require additional factor(s). Since the virus appeared to be widespread in U.S. swine population regardless of their clinical status related to PMWS, further work remains to determine the pathogenesis of PCV2 in conjunction with PMWS.The role of porcine circovirus type 2 (PCV2) in a newly emerged disease, postweaning multisystemic wasting syndrome (PMWS) was studied using two approaches: experimental inoculation and field-based case-control study. In the animal trial, 5-week-old gnotobiotic pigs free of PCV2 were inoculated intranasally and intramuscularly with PCV2 ISUVDL 98-15237 at a rate of 10⁴TCID₅₀/ml and monitored for a 35-day period. Inoculated pigs were viremic at day 7 post inoculation (PI) and developed virus-specific antibody response which was measurable by indirect fluorescent antibody and serum-virus neutralization tests. Viral DNA and antigens were detected in tissues with subtle histopathological changes (i.e., depletion of lymphocytes) at the end of the study (35 days PI). However, no clinical signs described in pigs affected by PMWS were observed in any of the inoculated animals during the study period. These inconclusive observations prompted a case-control study to assess the strength of association of PCV-2 and some other major swine viruses with PMWS. Cases were pigs affected by PMWS based on clinical and diagnostic criteria, whereas controls were clinically unaffected pigs. The proportion of case and control pigs positive for each virus was assessed and statistically compared for the association strength with PMWS. In addition, PCV2 isolates from 6 cases and 4 controls were selected and genetically compared