Porcine circovirus

Porcine Circovirus (PCV) is a single stranded DNA virus (class II), that is non-enveloped with an un-segmented circular genome. The viral capsid is icosahedral and approximately 17nm in diameter.

They replicate in the nucleus of infected cells, utilising the host polymerase for genome amplification.

There are 2 strains: Type 1 PCV and Type 2 PCV

Type 1 PCV (first identified in 1974) readily infects but is not known to cause disease in swine; it is the type 2 that has caused problems in recent years with the increasing occurrence of postweaning multisystemic wasting syndrome (PMWS) which over time results in significant depletion of lymphocytes; post mortem of diseased animals reveals enlarged lymph nodes and abnormal lung tissue.

It is still unclear whether type 2 PCV (first isolated in 1997) actually causes PMWS, as infection with the virus alone causes no clinical signs, it appears to work synergistically with parvovirus, perhaps with parvovirus activating a latent form of circovirus or weakening the immune system enough for PCV to take hold.