A Virus Once Found Only in Pigs and Birds Now Seen in Dogs

Researchers examining its potential to cause harm.


It has been known for more than 30 years that sphere-shaped pathogens called circoviruses can and have infected pigs worldwide, causing everything from pneumonia and kidney problems to wasting syndrome in young piglets that results in poor growth and high death rates. Circovirus has also caused beak and feather disease in parrots, cockatiels and other breeds; infectious anemia in chickens; and deadly infections in pigeons, canaries, and finches. Now a canine version of circovirus has been found in dogs and been associated with vomiting, diarrhea (sometimes bloody), and lethargy.

“Deadly, new circovirus disease sickening dogs around the country,” warned one headline. “Circovirus killing dogs across the country,” screeched another. “No vaccine,” blared a third. Is it really that bad?

The state of affairs

Some dog owners are getting nervous that the virus will spread to their pets, making them very sick, or worse. Is the alarm justified? First, consider that circovirus infection can by no means be considered an epidemic. Cases of dogs with the virus have been positively identified in California, Ohio, and Michigan. And by cases, we mean a handful, as in one in Ohio, two in Michigan, and a few dozen in California. So this is not a disease mowing down the canine population with alarming alacrity. In fact, it’s not mowing down the canine population at all. Many dogs in whom the circovirus is found are not even sick.

Yes, canine circovirus infections have been documented in dogs with vomiting and diarrhea. And it is conceivable that a circovirus infection, if virulent enough, can kill a dog. But the virus has also been identified in the stool of plenty of healthy dogs, suggesting that infection with circovirus does not always result in illness. Indeed, it is strongly suspected of having taken up residence in dogs as early as 2007, if not earlier, with some preliminary research indicating that it may be present in up to 11 percent of dogs. If it were uniformly deadly, it could not have flown under the radar for the better part of a decade.

What researchers are finding is that circovirus can go hand in hand with viruses that are known definitely to cause illness. They are hypothesizing that maybe it can make the signs of another virus worse or exist only as a co-pathogen rather than cause harm on its own. That’s what researchers at the Diagnostic Center for Population & Animal Health at Michigan State University are currently studying, as are scientists at the University of California, Davis. For instance, the California scientists published findings in the journal Emerging Infectious Diseases indicating that in the canine population they studied, more than two out of three dogs who had diarrhea tested positive not only for circovirus but also for other canine microorganisms that can cause illness. They also found circovirus in seven percent of perfectly healthy dogs.

To be sure, it is certainly possible for dogs who test positive for circovirus along with other pathogens to die of illness that reaches the point of causing organ failure and other deadly complications. The virus is not something that should be ignored or go unstudied. But panic would be more than an overreaction. That said, there are things dog owners can do to keep their dogs safer.

Steps to take

Certainly, if your dog shows signs that can possibly be associated with circovirus — vomiting, diarrhea (perhaps bloody), and lethargy — take him to the doctor. Such signs are vey nonspecific and may be attributable to any number of illnesses, including infection with another agent, viral or bacterial. Whatever the problem, you’ll have your dog in the right place for proper diagnosis and treatment.

Also, always practice good sanitation and hygiene. There is no evidence that dog circovirus can be transmitted to people or in any way cause people to become sick. But since all kinds of pathogens are transmitted from animals to people, thorough handwashing is good standard practice after handling a dog, especially after picking up waste when you walk one.

It’s also a good idea, to the extent possible, to keep your animal from coming into contact with another animal’s excrement and to curb your dog. It is not known to what degree the virus may be shed in stools, says the American Veterinary Medical Association. But theoretically, it’s possible. The circovirus, along with many other microorganisms, may potentially be spread from one dog to another by touching or close sniffing.


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