Indiana practitioner Tom Gillespie believes the variation in clinical signs is due to co-factors, both disease- and management-related. PCV2 is associated with several diseases, including postweaning multisystemic wasting syndrome (PMWS), reproductive disorders, porcine dermatitis and nephropathy syndrome (PDNS) and porcine respiratory disease complex (PRDC).

Pigs are struck most often between 8 and 16 weeks of age. Clinically affected pigs have been reported to lose up to 30% of their body weight within 7 to 10 days, and mortality has been reported as high as 50% in a few selected finishing flows, says Gillespie.

Crowding makes the problem worse. As producers strive for more pigs per sow per year, the problem amplifies in overstocked nurseries and finisher buildings. Of course, we've overstocked pigs for years without PCV2 problems, Gillespie adds, but the virus may have changed or other undetermined co-factors are involved.

The PRRS virus, for one, is a key co-factor. A PRRS-negative farm suffering a PCV2 outbreak may have a mortality rate of 6-8%, notes the Rensselaer, Ind., veterinarian. If the flow experiences both PRRS virus and PCV2 in the early finisher, mortalities skyrocket to 15-20% and higher.

One of the reasons PMWS has been categorized as a syndrome rather than an infectious disease is that full expression of the disease seems to require more than just infection by PCV2, says Pam Zaabel, DVM, director of swine health information and research for the National Pork Board.

PRRS virus, swine influenza virus and mycoplasma have all been isolated with the PCV2 in many cases of PMWS, notes Zaabel, who previously worked as a veterinarian in the Newton, Iowa, area for more than eight years. It's likely many swine operations are seropositive for PCV2, yet incidence of clinical disease varies greatly, she points out. In fact, most PCV2-positive pigs are clinically normal.

Drs. Pat Halbur and Tanja Opriessnig, both with Iowa State University's Veterinary Diagnostic Laboratory, provided the following control practices for PCV2-associated diseases. They are adapted from the 2006 Annual Meeting Proceedings of the American Association of Swine Veterinarians:

• Ensure an accurate diagnosis. PMWS can look like many other diseases. Physical examination of pigs, necropsies as necessary and laboratory confirmation of the infection and the presence of PCV2-associated lesions are required.
  
  

• Identify concurrent infections at the farm, site or system. Eliminate or minimize the effects of PRRS. This can be achieved through breeding herd stabilization, pig flow changes and vaccination.
  
  

• Evaluate the use and timing of vaccinations. If herd evidence suggests an association between vaccination practices and PCV2-associated disease, reevaluate the necessity and timing of the vaccines in use. Vaccination of pigs 5 to 7 weeks before PCV2-associated disease occurs is recommended. PCV2 infection typically occurs at 10 to 14 weeks of age.
  
  

• If the problem is PRDC due to PCV2 + PRRSV + M. hyopneumoniae, which is common, place vaccines 2 to 4 weeks prior to PCV2 infection. Use of anti-inflammatory drugs may be beneficial - 990 ppm acetaminophen for more than 6 weeks.

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