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Porcine Circovirus Type 2

Dr. Peter Bahnson
November 3, 2000

In the past few years, controversy has arisen over the importance of Porcine Circovirus type 2 (PCV 2) infection in growing pigs.

In the late 1990s, circovirus was reported in clinical cases of a wasting syndrome that affected multiple organ systems in weaned pigs (hence the name and acronym, "post-weaning multisystemic wasting syndrome," PMWS). Since that time, evidence has continued to mount that PCV 2 may cause the syndrome. Although infection with the virus alone causes little or no clinical signs, infection together with parvovirus, a common virus circulating in pig herds, has been shown to cause a wasting syndrome quite similar to that in reported clinical cases. There is also the potential that PRRS virus infection may increase susceptibility to PCV 2 infection.

Field-based evidence includes a Canadian study showing more nursery-pig diseases at infected farms than at non-infected farms. In addition, a descriptive study comparing cases of PMWS with cases of an apparently unrelated disease, Streptococcus suis infection, showed that PCV 2 was found in all of the PMWS cases, but none of the Strep. suis farms. The authors concluded that this was evidence to "confirm and extend previous findings documenting a consistent association of PCV 2 with PMWS."

Diagnostic testing for PCV 2 generally includes histopathology, specific staining of samples for virus (immunohistochemistry), and serologic testing. The specific stains are effective in documenting the virus.

The potential for PCV 2 to cause a wasting syndrome is relatively well established, and the infection is being detected at an increasing rate. The Iowa State University diagnostic laboratory, for example, reported nearly a four-fold increase in laboratory diagnosis of PCV/PMWS from 1998 to 1999. However, the impact of this infection relative to other growing-pig infections in commercial production is still up for debate, since it is not clear that infections necessarily cause disease.

No vaccines or treatments are currently available. The best protection at this point is strictly enforced principles of biosecurity, including strict sanitation and age segregation. Since infection with other viruses can increase the severity of the infection, steps to control concurrent disease may be justified. Good supportive care--including careful attention to environmental control--is especially important. Where indicated to control secondary or concurrent bacterial infection, antibacterial therapy can also be used.

Since controversy remains as to the relative importance of this infection in commercial production, producers need to keep an open mind, and veterinarians and producers alike need to keep abreast of the developing science in the area. For further reading, see the reference list at: http://www.cvm.uiuc.edu/~bahnson/circo

At least one thing is clear: Pigs are effective at reproducing viruses, and disease control or elimination remains, as always, an important component of efficient pig production.

Peter Bahnson, DVM, PhD Assistant Professor Veterinary Clinical Medicine and Veterinary Continuing Education/Public Service-Extension University of Illinois at Urbana Champaign

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