POST-WEANING MULTISYSTEMIC WASTING SYNDROME: STUDIES ON DISEASE PROGRESSION IN RELATION TO SERUM ANTIBODY LEVELS TO PORCINE CIRCOVIRUS TYPE 2 (PCV2) IN SOWS AND PIGLETS AND PCV2 VIRAEMIA IN YOUNG PIGS
F. McNeilly, I. McNair, G. Stewart, G. Allan, L.E. Green, C. Waldner, J. Ellis, D. Armstrong and S. Krakowka

Abstract
Blood samples were taken from 78 sows and 774 piglets on five farrow-to-finish farms in England.  Three of these farms had ongoing outbreaks of Post-weaning Multisystemic Wasting Syndrome (PMWS) and two were unaffected up to, and during, the time of the study. Sows were sampled 7 days prior to farrowing and piglets were sampled within the first 7 days of life. Serum antibody levels to Porcine Circovirus type 2 (PCV2) in all the samples were determined and bloods were analysed using the polymerase chain reaction (PCR) for PCV2 nucleic acid. The pigs were monitored for clinical disease for up to 16 weeks. All the pigs that died or showed clinical signs of PMWS were necropsied and tissues examined by immunohistochemistry (IHC) for PCV2 antigen.  When the tissues had histological lesions and a strong association with PCV2 antigen, the animal was deemed to have had PMWS.  These results were correlated with the PCV2 serum antibody levels and PCV2 nucleic acid content in the blood of the individual pigs in the first week of life.  The results indicate that there was no direct correlation between the levels of colostrum-derived PCV2 antibodies and the development of PMWS. However, they suggest that high levels of passively derived antibodies to PCV2 may delay the onset of PMWS. 

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