Porcine circovirus type 2 (PCV2) is associated with a group of production-limiting disease complexes in pigs. Now known as Porcine Circovirus Diseases (PCVD), these diseases include:
- Post-weaning Multisystemic Wasting Syndrome (PMWS)
- Porcine Dermatitis and Nephropathy Syndrome (PDNS)
- Enteric disorders
- Respiratory disorders
- Reproductive disorders
As multi-factorial diseases, PCVD was first identified in Western Canada in 1991. It is now recognized as a global, epizootic disease that causes significant economic losses to pig producers. Morbidity has been reported at 4-30% and sometimes as high as 50-60%, while mortality is usually 4-20%. PCV2 is present all over the world and most pigs have seroconverted against PCV2, indicating they have been exposed to the virus.
Clinical-apparent disease only occurs in a percentage of animals; the exact reason for this limited disease expression is still unknown. The same is true for the severity of the disease, which varies between countries or regions. Environmental conditions and the presence of other pathogens or diseases may contribute to disease expression.
According to Segales et al., 2012, the diagnosis of PCVD on a herd level is not only based on clinical signs and histopathology but also on viral load as an alternative method.
Taking into account the strong correlation observed between the amount of PCV2 antigen and/or nucleic acid and the severity of PCV2-SD histopathological lesions, alternative diagnostic methods avoiding the euthanasia of the pig have been suggested. Specifically, several studies have proposed real-time quantitative PCR (qPCR) thresholds in serum as indicative of PCV2-SD diagnosis: 104.7 (Harding et al., 2008), 106.21 (Grau-Roma et al., 2009), 106.91 (Fort et al., 2007), 107 (Brunborg et al., 2004; Olvera et al., 2004; Segalés et al., 2005b) and 107.43 (Grau-Roma et al., 2009) viral copies/mL.
Porcine circovirus is associated with PCVD. It is a small, resistant, ring-shaped, single-stranded DNA virus.
Two serotypes have been isolated:
- Type 1 causes no known disease
- Type 2 is ubiquitous in pig populations and causes disease symptoms related to PCVD
There are several different strains (biotypes and genotypes).
Experimentally, colostrum-deprived piglets inoculated with PCV2 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 PCV2 infection is widespread throughout the pig population, and until the winter of 2004, only a small proportion of seropositive 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.