What Is Circovirus in Dogs?

Veterinary pathologist Dr. Dubiski won the prestigious Casey Award for his discovery of canine circovirus in a little beagle.
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As late as 2012, small animal veterinarians didn’t even know to look for circovirus in pups with severe gastrointestinal issues. Until then, circoviruses -- small and hardy viruses named for their circular, single-stranded DNA -- only had been seen in pigs and birds. That was until a very unlucky young beagle, his committed owners and determined veterinary pathologists came along.

Patient Zero

In April of 2013, a year-old beagle was taken to his veterinarian with severe vomiting and bloody diarrhea. His condition deteriorating, the family opted to bring him to the University of California, Davis Veterinary Teaching Hospital, a top-ranked facility. Even with continued, aggressive treatment, he worsened. His family, understanding the pup's poor prognosis, made the decision to euthanize. In what would turn out to be a pivotal decision, they granted permission for a necropsy. The university's pathologists quickly ruled out bacterial and infectious suspects that would typically cause intestinal disease -- parvo, Salmonella, Giardia, coronavirus and others. Certain there was more to this pup's tragic story, Dr. Kubiski and his team sent samples of his liver for viral analysis. The results shocked them. The beagle -- “Dog 1” as he’ll forever be known -- had been infected with a novel canine circovirus, now called dog-CV.

A Game Changer for the Pork Industry

Circovirus was first identified in pigs in 1982. This first virus -- PCV1 -- was common, but considered nonpathogenic. In the late 1990s, a new circovirus appeared in pigs; one that was far less benign and came with catastrophic consequences for the pork industry. PCV2 causes a host of diseases, some with fatality rates as high as 80 percent. Today, nearly all U.S. pig herds are seropositive, meaning they've been exposed to the virus. Circoviruses also have been isolated in birds. Beak and feather disease in parrots, parakeets, budgies and cockatiels, anemia in chickens and infections in pigeons have all been characterized as circoviruses. Canine circovirus is more closely related to the swine version than the bird.

Sounding the Alarm

A year after the first case of canine circovirus was discovered in California, veterinarians in Ohio and Michigan sounded alarm bells after seeing profoundly sick and dying dogs in their own states. All shared symptoms similar to the little beagle: lethargy, vomiting and bloody diarrhea. Circovirus was positively identified in one of the eight sick dogs in Ohio and two of the six dogs that died in Michigan. In response to these incidents, the American Veterinary Medical Association issued guidance for veterinarians and the Michigan State University Diagnostic Center for Population and Animal Health added two real-time tests for canine circovirus to their catalog.

Still a Mystery

How the pups contracted circovirus is still a mystery. As with other viruses, direct contact with an infected animal or its fluids is likely to increase risk of infection. In pigs, circovirus can be contracted through an infected animal’s feces or respiratory fluids. The young beagle in California, and three of the pups who died in Ohio -- though none of the three positively identified with circovirus -- all recently had been boarded at kennels or dog day care facilities. While these facilities are not the cause of the infections, it’s a good reminder to avoid canine crowds if your dog is sick, elderly or otherwise immunocompromised.

Don't Panic

The American Veterinary Medical Association advises owners not to panic. While there is still much to learn about canine circovirus, scientists have confirmed that not all infected dogs become ill. They’re also seeing that, as with pigs, co-infection with other diseases is more likely to lead to sick pups. In the case of the two deaths in Michigan, both dogs had other diseases -- one with parvovirus -- which likely contributed to their deaths. Bottom line: If your pet is vomiting and has diarrhea, it’s likely not circovirus, but it could be any number of bacterial or infectious conditions, some life-threatening. As with most medical conditions, early veterinary intervention often makes the difference between a happy pup and a heartbroken family.