ThePigSite Quick Disease Guide
Post Weaning Multisystemic Wasting Syndrome (PMWS)
The disease is associated in part with a porcine circovirus (PCV), so called because its DNA is in the form of a ring. It is extremely small and hardy. There are two serotypes, Type 1 causes no known disease. Type 2 can be found in the lesions and can be isolated in pure culture. There are several different strains (biotypes and genotypes). Antibodies to circovirus type 2 have been detected in pig sera collected in Belgium in 1985 but the clinical disease was not described until 1991 in Western Canada. It has since become widespread in North America and Europe.
Young experimentally inoculated colostrum deprived pigs given Type 2 alone sometimes, develop typical lesions. However, they are more likely to develop lesions if another virus, such as porcine parvovirus (PPV) or porcine reproductive and respiratory syndrome virus (PRRSV), is inoculated at the same time. Naturally occurring clinical cases in the field seem always to have a dual infection with PCV Type 2 and some other virus but most pigs which are infected with PCV and PRRS do not develop clinical PMWS.
Serum surveys in Europe and North America have shown that infection has spread widely through the pig population but only a small proportion of seropositve herds have a history of clinical disease. It seems that most infections are sub-clinical. It is not known why some infections result in disease. Piglets may become infected before weaning.
SymptomsWeaners & Growers
- PMWS tends to be a slow and progressive disease with a high fatality rate in affected pigs.
- Starting usually at about 6 - 8 weeks of age, weaned pigs lose weight and gradually become emaciated. Their hair becomes rough, their skins become pale and sometimes jaundiced.
- Sudden death.
- Enlarged peripheral lymph nodes.
- May show diarrhoea.
- May show respiratory distress caused by interstitial pneumonia.
- Post weaning mortality is likely to rise to 6 - 10% but is sometimes much higher.
- Clinical cases may keep occurring in a herd over many months. They usually reach a peak after 6 - 12 months and then gradually decline.
Causes / Contributing factors
- Infected faeces.
- Mechanical means via clothing, equipment, trucks etc.
- Possibly birds and rodents.
- Circovirus has also been detected in semen from apparently healthy boars.
- It is not known what other ways the virus spreads between pigs or between herds.
- Mixing and stress.
- Continual production.
- High stocking densities.