Print This Article

There are several schools of thought as to why porcine circovirus type 2 (PCV2) is identified as the cause of mortality in so many pigs, even though the virus has been present in swine for decades.

Some veterinarians feel the variation in clinical expression of PCV2-associated diseases such as pneumonia, postweaning multisystemic wasting syndrome (PMWS), enteritis and porcine dermatitis and nephropathy syndrome (PDNS) are due to stocking density, animal fl ow situations and to a lesser extent, geography and genetics. Th e presence of PCV2 antibody in non-clinical herds clearly indicates that PCV2 by itself oft en does not lead to severe disease.

Indiana practitioner Tom Gillespie, who is heading an AASV task force charged with gathering case studies on circovirus-related syndromes, believes the variation in clinical signs is due to cofactors, both disease and management-related.

Th e task force also has pinned down a name on the syndrome. But due to the expanding spectrum of diseases now associated with PCV2 infection, it is appropriate to refer to the clinical manifestations as PCV2-associated diseases (PCVAD), rather than just PMWS; an acronym, Gillespie says, that is not totally acceptable today.

PRRS MAKES PCVAD WORSE

A key cofactor to PCVAD is porcine reproductive respiratory virus (PRRSV). A PRRS-negative farm suff ering a PCV2 outbreak may have a mortality rate of 6-8 percent, notes the Rensselaer, Ind., veterinarian. If the fl ow experiences both PRRS virus and PCV2 in the early fi nisher, mortalities skyrocket to 15-20 percent and higher.

Indiana is just one state aff ected by PCVAD. It’s also killing pigs in the southeast and is rampant in the eastern provinces of Canada. “People say we are importing the virus from Canada, but I’ve had problems in fl ows that never brought in an animal from Canada, nor are they near another unit that has imported animals, so it’s diffi cult to lay blame on our Canadian colleagues,” says Dr. Gillespie.

Severe clinical signs of PCVAD are still best described as a chronic weight loss syndrome, he points out. “It is amazing as a practitioner to watch these pigs stand at the feeder eating and lose weight,” says Gillespie. “There is something there we don’t fully understand that creates a catabolic condition in these animals.”

Circovirus strikes pigs most oft en between 8 and 16 weeks of age. Clinically aff ected pigs have been reported to lose up to 30 percent of their body weight within 7 to 10 days, and mortality has been reported as high as 50 percent in a few select finishing flows.

Crowding certainly exacerbates the disease problem and the drive for more pigs per sow per year has amplifi ed this issue, Gillespie continues. “Th e business plan for many clients has been to capture sow effi ciency. Few facilities were built to handle 25 to 30 pigs per sow, so we overstock the nursery and fi nisher buildings. Yes, we’ve overstocked pigs for years so why all of a sudden are we having PCV2 problems? Maybe there has been a change in the virus or there are other undetermined cofactors.”

OTHER DISEASE MANIFESTATIONS

Clinically, PCV2 is easily confused with ileitis. Observations in the U.S. indicate circovirus is linked to enteric eff ects, according to John Kolb, DVM, biologics manager for Boehringer Ingelheim Vetmedica, Inc. It has shown an ability to thicken the gut, similar to Lawsonia ileitis on fi rst inspection, although the lesions are easily diff erentiated with histopathological examination, he says.

Gillespie recalls four cases where pigs placed into the fi nisher had typical appearing diarrhea, but there was neither salmonella nor ileitis present. Th e only thing they could determine was PCV2 infection. PCV2 diarrhea, in fact, is sometimes seen in a group prior to clinical PCVAD.

Although it varies from region to region, PDNS is also part of the PCV2 disease complex. Gillespie has found many more incidents of skin lesions caused by PDNS in nurseries with acute stocking problems.

As far as treatment and control, Gillespie’s diagnostic approach is to fi nd coinfections fi rst and implement an action plan. Serology is limited as far as PCV2 diagnosis, since there isn’t a farm that is not positive to the virus.

Secondly, there is almost always an increase in antibiotic therapy. Gillespie prescribes aspirin, electrolytes and chlortetracycline. “But circovirus should be treated as any other virus,” adds the veterinarian. “It still comes down to the same type of management interventions true for any other respiratory disease.”

Th e Indiana practitioner admits that PCV2 has been devastating herds around the world, yet the U.S. pork industry has not treated it as an emerging disease. “We were not as proactive as we should have been. We need to get a grasp on this disease and help our clients. Th at’s my personal motivation.”