Porcine Circovirus (Associated) Disease (PCVD) causes wasting and mortality in piglets from 6 weeks of age onwards. Clinical disease was first described in Western Canada in 1991. The syndrome is becoming of considerable concern in modern pig production especially in Canada, the US and Europe.
PCVD is a multifactorial disease. Porcine Circovirus type II (PCV-2) plays a major role, but management factors and other disease agents are also relevant.
There are several different strains (biotypes and genotypes).
Experimentally, colostrum deprived piglets inoculated with PCV-2 may develop typical PCVD lesions. They are however more likely to develop lesions if inoculated simultaneously with another virus, such as porcine parvovirus (PPV) or porcine reproductive and respiratory syndrome virus (PRRSV).
Serum surveys in Europe and North America have shown that PCV-2 infection is widespread throughout the pig population and until the winter of 2004, only a small proportion of seropositve herds had a history of clinical disease in North America. After 2004 many farms in North America experienced outbreaks of PCVD. It is not known why some infections result in disease while others are subclinical.
Environmental factors, such as drafts, overcrowding, poor air quality, co-mingling of age groups or other stressors exacerbate the severity of the disease.
Signs are usually seen from about 6 - 8 weeks of age onwards:
Piglets affected by PCVD
Post weaning mortality is likely to rise to 6 - 10% but is sometimes much higher. Mortality peaks in affected piglets around 9-12 weeks of age. Signs of disease are usually seen between 2 and 6 months of age.
Clinical cases may keep occurring in a herd over many months. They usually reach a peak after 6 - 12 months and then gradually decline.
The clinical syndrome (stunting, pallor, dyspnoea, jaundice, diarrhoea and mortality) suggests PCVD, but confirmation is based on the pathological findings and demonstration of the virus in tissues. As post mortem lesions are variable it is often necessary to post mortem several pigs.
Oedematous kidney with white spots visible on the cut surface
Haemorrhages in the gastric mucosa
Diagnosis is based upon the presence of PCV type 2 histological lesions in affected organs. Immunohistochemistry is used to demonstrate PCV in tissues. Microscopically these lesions are characteristic and diagnostic particularly if the Circovirus is demonstrated in them.
Apart from support therapy, nursing and antimicrobials to control secondary bacterial infections, there is no specific treatment for PCVD. With nursing some animals may recover. This is not possible on any large scale and high mortality often persists under farm conditions.
Two vaccine options are available from Merck Animal Health: