General Information about PCV2
Porcine Circovirus Type 2, or PCV2, is a very small circular-arranged DNA virus that belongs to the Circoviridae family. PCV2-infection is widespread and essentially all pig herds are infected with PCV2 but relatively few have PCV2-associated disease (PCVAD), which includes severe systemic PCV2 infection or Postweaning Multisystemic Wasting Syndrome (PMWS), PCV2-associated pneumonia as a part of the Porcine Respiratory Disease Complex (PRDC), PCV2-associated enteritis, PCV2-associated reproductive failure, and Porcine Dermatitis and Nephropathy Syndrome (PDNS).
Postweaning multisystemic wasting syndrome (PMWS) was first described in 1991 in Canada. PMWS is a serious manifestation of PCV2 infection. PMWS is characterized by severe loss of weight (wasting) and generalized lymph node enlargement. Today we know that there are several PCV2 associated diseases (PCVAD) and severe systemic PCV2 infection remains as the most important manifestation. PCV2-associated Porcine Respiratory Disease Complex (PRDC) is also a very commonly diagnosed PCVAD in the U.S. Less commonly diagnosed diseases include PCV2-associated Enteritis, PCV2-associated Reproductive Failure, and Porcine Dermatitis and Nephropathy Syndrome (PDNS).
The hallmark microscopic lesion of pathogenic PCV2-infection is lymphoid depletion associated with PCV2 antigen or nucleic acids. Diagnosis of PCVAD requires microscopic examination and demonstration of the presence of lymphoid depletion or lymphohistiocytic inflammation of other organ systems and association of PCV2 antigen with the lesions. This is typically done by immunohistochemistry (IHC).
PCV2-infection is widespread and essentially all pig herds are infected with PCV2 but relatively few have PCVAD. In many cases, PCV2 infection requires a trigger such as coinfection with other pathogens (PRRSV, Mycoplasma hyopneumoniae), immune stimulation of the host, or other stressors to trigger PCV2 infection to progress to PCVAD. Host genetics may also markedly affect the outcome of PCV2 infection and there is increasing evidence of differences in virulence among PCV2 isolates.