Young Pigs

Photo courtesy of the Pork Checkoff.

A new virus has been recently found inside sow herds across many countries, including the United States. The virus, porcine circovirus type 3 or PCV3, is similar in structure to porcine circovirus type 2, but there is still very little known about it.

“At the moment, there are a lot of papers being published of where this virus is at, pretty much it’s in Europe, Asia, South America, U.S.,” said Dr. Darin Madson, DVM with Iowa State University, during a recent SwineCast episode of At the Meeting honoring Dr. Bob Morrison. “It is very prevalent in all the swine-producing countries.”

Two different groups, the University of Minnesota working with California, University of California, Davis and Iowa State University working with Kansas State University, discovered the PCV3 virus.

Minnesota and California researchers were looking at young pigs that were slow to start and had myocarditis lesions. Iowa and Kansas researchers were looking at sows that had an increased prevalence of mummy piglets at birth.

“Lo and behold, two different groups working separately about the same time and found the same virus in the U.S.,” said Dr. Madson. “Once they were found, they were sequenced, the whole genomes were sequenced.”

With the genome of the virus sequenced, it was easy for other countries to develop PCR tests to begin looking for the virus in their herds. They also started looking for the virus in samples from their stored archives.

“When you look back at the archive samples, there were only a few of those papers being published at this point, but they indicate that the virus probably was found back in the mid-1990s, 1996 in some cases in Europe or in the middle of the Asia area,” he said.

This would indicate that PCV3 is not so much an emerging, new pathogen, but rather, because testing technologies have improved, it is only just now being discovered.

“Because we found it by metagenomics, we're testing for it,” he said.

The research into PCV3 is just beginning. It is – as of yet – unclear if this virus has any actual impact to pigs.

“The case definition is lacking for PCV3 right now,” he said. “There is no generalized acceptance of what the syndrome may be.”

While the virus has been found in poor starting piglets and sows with increased mummies or other reproductive problems, that suggests it has an impact on the animals, but does not prove it. There could be other variables or infections present causing those issues.

“There is a lot of vague things at this point in time, because one of the downsides is that we haven't been able to isolate the virus,” he said. “To that extent then, we haven't really been able to put this virus into pigs in a research setting to understand what this virus may do in pigs that are naive to it.”

What is known is that the virus is only about 33-35 percent similar to PVC2 on the outside of the virus. It is also a little over 200 base pairs larger. This means it is a completely different organism than the PCV2 virus.

“We do not think, based on the percent difference, that this virus would have any correlation at all with immunity to PCV2 or vice versa,” said Dr. Madson. “Meaning, PCV2 vaccines are likely not to protect against infection of PCV3.”

The next steps into researching the PCV3 virus are to continue to test samples for it, but also try to isolate and grow the virus so it can be introduced to pigs in a research setting. This has been a challenge for the research groups working with the virus.

“When you can't grow the virus, you reverse genetics, you make an infectious clone,” he said. “Basically, you make the virus from scratch yourself based on the sequences. At this point, I know that multiple groups have been trying to do that.”

A few groups believe they are close to having a clone of the PVC3 virus. Once they have that accomplished, the virus will be introduced to healthy pigs and more will be learned about this virus.