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Disease associated with porcine circovirus type 2 (PCV2) is a complex mix of clinical signs and tissue lesions.

The pathogen has been in U.S. swine populations for decades, but is emerging as a virulent epidemic with a new name – porcine circovirus associated disease, or PCVAD. And because its signs and lesions mimic other deadly pathogens, PCVAD is tough to diagnose.

That’s why Boehringer Ingelheim Vetmedica developed a diagnostic procedure with the acronym MAGIC, which stands for Monitoring Assignment for Global Insight of Circovirus disease. Its goals are to identify common coinfections or risk factors during periods of high mortality and find control options.

A 2006 pilot study using the protocol gives producers and swine practitioners an indepth look at the roles pathogens play in cases of high finishing death loss, specifically PCV2, and the importance of diagnostics.

Study results held a few surprises for the 60 participating herds. Those farms represented a third of the country’s pigs.

Serum and tissue samples were collected from a cross-section of animals from each farm to identify pathogens before, during and after peak mortalities. All the samples went to the Iowa State University Veterinary Pathology Laboratory under the auspices of pathologist Dr. Kent Schwartz.

Testing methods included serum antibody tests, PCR and immunohistochemistry. Samples were screened for PRRS, influenza, Mycoplasma hyopneumoniae and PCV2, as well as bacterial cultures.

A paper authored by Dr. Schwartz of Iowa State University and Dr. John Kolb, biologics D manager for Boehringer Ingelheim Vetmedica, Inc., provided these observations from MAGIC:

• • Clinically unaffected PCV2 positive pigs had very similar lesions to clinically affected pigs. These animals may have been simply preclinical, not yet fully affected or in the process of clearing viral infection at the time of sampling. • Pigs with concurrent disease generally had more PCV2 antigen and compatible lesions associated with concurrent disease process. • Lesions vary considerably in tissue location and severity between individuals within groups, among groups, between timing of selection and between farms. • In some PCVAD cases, microscopic lesions and positive IHC staining were found only in the enteric system. • Respiratory disease is common and it was not unexpected that lungs were frequently diseased in this study. PCV2 lesions in the absence of other detected pathogens in lungs were usually not severe. • Kidneys frequently had multifocal to locally extensive inflammation, something the Iowa lab rarely saw a decade ago. Lesions ranged from mild to severe, with features indicative of end-stage kidney disease.

Another key finding from the Iowa diagnostic lab was this: PCV2 loves inflammation.

“And there are many things that cause inflammation, meaning samples are needed of each organ system to determine what is driving that inflammation,” Kolb pointed out. “Once we do that, we can better understand cofactors and decide how to treat the whole picture.”

The protocol did find what they were looking for: lesions consistent with PCVAD were located in samples from every farm.

That did not surprise the researchers. Nor did the fact PRRS was the most common pathogen identified as a concurrent infection with PCV2.

What did surprise them was the second most common infection: salmonella.

Another surprise was the fact mycoplasma came in fourth as a concurrent infection.

Coming in third as the most common cofactor was swine influenza virus, which was present in 30 percent of the cases.

The MAGIC study showed the importance of thorough diagnostic protocol to clarify the roles of swine pathogens in cases of high finishing mortality. Only a complete approach can detect the critical coinfections that help drive clinical severity of PCV2-associated disease.