THE EVOLUTION OF PORCINE DERMATITIS AND NEPHROPATHY SYNDROME (PDNS) AND POST-WEANING MULTISYSTEMIC WASTING SYNDROME (PMWS) ON ONE UNIT
by S.H. Done, D. Hicks, L. Terry, A.C.J. Gresham, S. Williamson, D. Chennells, L. Taylor, D. Armstrong, T. Demmers, R. White and C. Wathes

Abstract
The longitudinal evolution of PDNS/PMWS in one herd is described. All the major ingredients were present in the herd: PRRS, Swine influenza, PRCV, PCV-1, PCV-2, PCMV, PPV and most potential bacterial pathogens including P.multocida (but not toxigenic type D which is associated with progressive atrophic rhinitis) and Actinobacillus pleuropneumoniae, although these have occurred in the past. Post-mortem examination was carried out on batches of pigs at five, ten and twelve weeks of age and at slaughter at 85kg. These pigs were the subject of a study of the effects of respiratory pollutants, which was carried out over a period of four years commencing in 1999.
???? Most of the pigs in this study have shown enlarged hyperplastic tracheobronchial lymph nodes and interstitial pneumonia since the start of the experiment; but now this has progressed to a full-blown PMWS outbreak.
???? In the autumn of 2001, clinical and pathological signs consistent with PMWS were identified. Pigs were grossly pale, wasted, hairy and with enlarged lymph nodes. The enlarged lymph nodes from affected pigs now show lymphocytic depletion and giant cells whereas this was not evident before. Immunohistochemical positivity for PCV-2 has been demonstrated in the lymph nodes of these pigs. This, together with the gross and pathological findings, confirms the presence of PMWS in this group of pigs.
???? This sequential longitudinal study is the first to follow the clinical and gross pathological progression into PMWS and PDNS and the changes in the lymph nodes. This study suggests that hyperplastic lymph node changes may precede the gross pathology, clinical signs and the typical histopathology described in the literature (lymphocyte depletion, giant cells and inclusions). These changes may represent the classical porcine respiratory disease complex (PRDC) situation seen in the USA, which is customarily associated with circovirus infection (Sorden, 2001).

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