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Postweaning Multisystemic Wasting Syndrome (PMWS)
First identified in 1982, porcine circovirus (PCV) is a DNA virus and member of the Circoviridae family. PCV infections may interfere with normal immune functions and Postweaning Multisystemic Wasting Syndrome (PMWS) has now been described worldwide.
Clinically, the syndrome is characterised by wasting, paleness of the skin, dyspnea, diarrhoea and icterus (jaundice). In 1997, the presence of porcine circovirus (PCV2) antigen was demonstrated in lesions of animals affected by PMWS.
Since 1999, PCV2 has been suggested to play a role in reproductive disorders, porcine dermatitis and nephropathy syndrome (PDNS), porcine respiratory disease complex (PRDC), proliferative and necrotizing pneumonia (PNP) and congenital tremors, but it remains a controversial issue.
PMWS most commonly affects pigs from 2 to 3.5 months of age. The clinical signs include weight loss, emaciation, tachypnea, dyspnea, jaundice, enlarged lymph nodes and pallor. Less common signs are diarrhoea, coughing, pyrexia, gastric ulceration, sudden deaths and central nervous system disturbances.
Some trials have fully demonstrated that PCV2 can be itself, without any other apparent triggering factor, the cause of PMWS. Some clinical signs may also be caused in part or exacerbated by secondary infections.
PCV2 can be transmitted vertically and cause reproductive failure in the absence or presence of other pathogens.
PMWS has been observed in almost all types of farms. Serologically, PCV2 infections are spread worldwide. Carlos Pijoan, PhD (Pigletter, July 2002) wrote that PMWS seems to be more prominent in regions that have both a high pig density and high level of disease in their pig population.
Emergence of PMWS disease, and not the PCV2 virus, may have been caused by changes in management practices, stimulation of the immune system, a change in host genetics, or emergence of other agents that enhance disease severity during mixed infections. Post-weaning mortality is 5 to 20 percent.
Factors that trigger PCV2 infection to progress to full-blown PMWS may be in the form of coinfecting pathogens (PPRS, PPV, or another virus or bacteria), immune stimulation such as adjuvants and vaccines, environmental factors (ammonia, endotoxins), or the consequence of other stressors such as transport and mixing of pigs.
The final diagnosis of PMWS is established based on three criteria:
- Presence of a clinical picture compatible with PMWS
- Presence of characteristic histopathological lesions
- Detection of PCV2 within the lesions in tissues of affected pigs
Main areas for prevention and control include reducing pig-to-pig contact, improving hygiene and husbandry practices, reducing stressors, providing correct nutrition and controlling concurrent diseases.
In the absence of a licensed vaccine, management strategies need improvement. Use of immunomodulation products, feedback on viscera and blood of affected animals, and serum-therapy (subcutaneous injection of PCV2 hyperimmune sera from commercial 100 kilogram pigs at 7 days after weaning) may be effective.
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Article made possible through the contribution of Trejo & Associates (TAEI).
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