PCV3: A challenge independent from PCV2
Anyone involved in raising pigs is aware of porcine circovirus type 2 (PCV2), but new on the scene is porcine circovirus type 3 (PCV3). Although the two viruses are both circular DNA viruses in the same family, they are separate and distinct.
“When you look at the two viruses from a molecular level, they’re very different,” Emily Byers, DVM, Prestage Farms, told Pig Health Today. Her extensive experience involves the virus in a gilt-acclimation site tied to a 7,500-head sow farm and the related down-stream grow/finish production.
Complicating matters, PCV3 can present similar clinical symptoms as PCV2 — post-weaning multi-systemic wasting syndrome, porcine dermatitis and nephropathy syndrome, and porcine circovirus associated disease (PCVAD).
“Typical clinical signs that would be attributed to PCV2 in growing pigs, gilts and sows,” Byers noted. “We’d have sows that would be healthy one day and dead the next.”
But overall, the disease progression was gradual. She pointed out that from the time clinical signs started to surface until the farm received a confirmed diagnosis, it took about 18 months. Part of that was due to not having a polymerase chain reaction (PCR) test available to identify PCV3. Byer would send tissues in for testing and get lymphoid, skin and kidney lesions suggestive of PCVAD, but PCR and immunohistochemistry test results would consistently come back negative for PCV2.
“We knew something was not quite right,” she recalled. Eventually a newly developed test detected PCV3 in mummified fetuses. Because there is no vaccine or known treatment options, Byer said “we tried to ride it out. We did not want to pursue feedback or a live-virus inoculation because we felt that was too uncontrolled. Over time, performance improved.”
But there remain many unknowns, including how the virus entered the herd. She added that the sow herd was negative for porcine reproductive and respiratory syndrome and remained so.
Based on limited work on PCV3, Byers believes that it, like PCV2, is widespread in US herds. She and her colleagues don’t know what triggered the virus to cause disease. And because it’s a different virus, the assumption is that vaccinating pigs for PCV2 will not provide protection against PCV3.
“There’s a huge knowledge gap [about this virus],” she said. “We’re starting to get some traction, but we have a lot of research to do on this virus to fully understand the implications.”
Meanwhile, her advice is for producers and veterinarians to be vigilant with this virus, especially when there are clinical signs.
“I think back to reports of PCV2 as it was emerging; there were sporadic reports of similar disease in grow/finish pigs,” Byers recalled. “Then over time it grew into what is now considered among the most significant pathogens in our industry.”