Dynamics of porcine circovirus type 2 infection in a herd of pigs with postweaning multisystemic wasting syndrome

<jats:title>Abstract</jats:title> <jats:p> <jats:bold>Objective</jats:bold>—To determine the pattern of infection for porcine circovirus type 2 (PCV2) in a herd of pigs with postweaning multisystemic wasting syndrome (PMWS).</jats:p> <jats:p> <jats:bold>Animals</jats:bold>—29 sows and 250 pigs.</jats:p> <jats:p> <jats:bold>Procedure</jats:bold>—Blood samples were collected from all 3-, 7-, and 12-week old pigs and 59 pigs at 28 weeks of age. Pigs that died during the study were necropsied. Porcine parvovirus and PCV2 antibodies were assayed. A polymerase chain reaction (PCR) was used to detect PCV2 genome in serum of selected pigs.</jats:p> <jats:p> <jats:bold>Results</jats:bold>—The PMWS started when pigs were 8 weeks old, with a prevalence of 30% in 8- to 10-weekold pigs. Eighty-three pigs died during the period between 3 and 12 weeks of age. Microscopic lesions consistent with PMWS were observed, and PCV2 nucleic acid was detected (50 of 68 pigs). Antibodies to PCV2 decreased from 3 to 7 weeks of age, increased at 12 weeks of age, and were maintained until 28 weeks of age. One sow had a positive result for PCR of serum. Nine, 37, and 8 pigs had PCV2 genome in serum obtained at 7, 12, and 28 weeks of age, respectively.</jats:p> <jats:p> <jats:bold>Conclusions and Clinical Relevance</jats:bold>—Infection with PCV2 coincided with severe clinical signs; however, infected 28-week-old pigs did not have evidence of disease. Immunity declined over time in young pigs. A long duration of PCV2 viremia was apparent in a high percentage of infected pigs, which may affect transmission and persistence of the virus in a herd. (<jats:italic>Am J Vet Res</jats:italic> 2002;63:354–357).</jats:p>