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Bulletin No. 17 - Winter 2003
VirologyPMWS-PCV2-PCVD-PDNS
CHARREYRE C
PMWS-Immunologic stimulation and clinical signs.
Proceedings of the ISU Swine Disease Conference for Swine Practitioners 2003: 161-169
To date our knowledge of the pathogenesis of PMWS is still incomplete. However several key points have been established and are reported in this paper. Virus properties are described as well as the clinical signs with reference to experimental reproductions of PMWS. The role of lymphoid organs in PCV2 infection is emphasized but nonlymphoid organs involvement (lung, gastro-intestinal tract and more specifically liver) is the true cause of death in PMWS affected pigs. Variable and mild peripheral lymphadenopathy, especially in the bronchial lymph nodes, is associated to subclinical PCV2-infection whereas multifocal to diffuse mixed angiocentric granulomatous inflammation is to be considered as diagnostic for clinical PMWS. Histiocytic, monocytic and lymphatic cells are target cells for PCV2 but they do not allow PCV2 replication. Thus, though probably including parenchymal cells, the primary site of replication of the virus is still unknown. As replication goes on, phagocytic cells accumulate the virus in their cytoplasm and could disseminate the virus throughout the pig body in this way. Early or inappropriate immune stimulation is an aggravating factor for PMWS and co-infection with porcine parvovirus (PPV), porcine reproductive and respiratory syndrome virus (PRRSV) or Mycoplasma are considered as triggering factors.
