PCV-2

Porcine circovirus (PCV) is a single-stranded DNA virus (class II), that is nonenveloped with an unsegmented circular genome. The viral capsid is icosahedral and approximately 17 nm in diameter. PCV is a member of the virus family Circoviridae.

PCVs are the smallest viruses replicating autonomously in eukaryotic cells. They replicate in the nucleus of infected cells, using the host polymerase for genome amplification.

There are 2 strains: type 1 and type 2. Porcine Circovirus Associated Disease is caused by porcine circovirus type 2 (PCV2).

PCV-1 readily infects, but is not known to cause disease in swine; the type 2 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; postmortem examination of diseased animals reveals enlarged lymph nodes and abnormal lung tissue.

PCV-2 causes PMWS. However, viral infection by itself tends to cause only mild disease, and co-factors such as other infections or immunostimulation seem necessary for development of severe disease. For example, concurrent infection with porcine parvovirus or PRRS virus, or immunostimulation lead to increased replication of PCV-2 and more severe disease in PCV-2-infected pigs.