Circovirus in Dogs: Symptoms, Causes, and Treatment

By Samantha Drake

In 2013, several dogs in California, Ohio, and Michigan became sick, and initial evidence pointed to dog circovirus as the possible cause. Little was known about the illness, and early media reports sparked fear among dog owners. Now, researchers and veterinarians say the prevention and treatment of dog circovirus involves a large dose of common sense, yet the source of the illness and how it functions remain largely a mystery.

What Is Canine Circovirus?

Circoviruses are small viruses that can also infect pigs and birds. Researchers first discovered dog circovirus in 2012 as part of a screening for new viruses in canines, according to a fact sheet published by the American Veterinary Medical Association (AVMA).

In 2013, staff at the University of California–Davis School of Veterinary Medicine treated a dog who was vomiting and had diarrhea before euthanizing it when its condition continued to deteriorate. A necropsy found that the animal had canine circovirus, says Dr. Steven V. Kubiski, who at the time was a resident who treated the dog and now works in the school’s Department of Pathology, Microbiology and Immunology.

Further research eventually identified older cases of other dogs with the circovirus, some as early as 2007, and that it was “present in dogs with diarrhea and dogs that are healthy,” Kubiski notes. The question was—and remains—why do some dogs get sick and other don’t?

Symptoms and Treatment of Circovirus in Dogs

Symptoms of dog circovirus including vomiting, diarrhea (which may or may not be bloody), lethargy, and sometimes vasculitis (inflammation of blood vessels) and low platelet counts. There’s no specific treatment for dog circovirus. Once a veterinarian has been consulted, dog owners just have to “let it run its course,” says Kubiski, adding, “I don’t think dog circovirus is anything that people should be on edge about.” Supportive treatment like medicines to relieve nausea and fluid therapy can help keep dogs comfortable and prevent complications from developing.

It’s also important to keep in mind that diarrhea and vomiting can be linked to a wide variety of canine ailments and doesn’t necessarily indicate the presence of dog circovirus. “Diarrhea is one of the most non-specific symptoms,” Kubiski notes. Common causes of vomiting and diarrhea in dogs include other viral infections (e.g. parvovirus), bacterial infections, intestinal parasites, organ dysfunction (e.g. kidney or liver disease), exposure to toxins, inflammatory disorders, cancer, anatomic abnormalities, and dietary indiscretion.

Of course, regardless of the reason, owners should always contact a veterinarian promptly if their dog is vomiting and has diarrhea.

Causes of Dog Circovirus: Questions Persist

Dog circovirus was suspected to be the possible cause of illness and death of dogs in several parts of Ohio in fall 2013, but was ruled out as the primary cause of illness in these cases, according to the AVMA. Then, the Michigan State University Diagnostic Center for Population and Animal Health (MSU-DCPAH) in Lansing, Michigan, began investigating reports of suspected dog circovirus in the state.

But the findings only added to the mystery of what was causing dogs to become sick. Researchers again discovered that the majority of dogs showing signs of illness who tested positive for dog circovirus were also infected with other disease-causing bacteria and viruses, the DCPAH said in a 2013 statement. In addition, researchers also found the presence of dog circovirus in the feces of healthy dogs.

“Because of the likelihood for additional infections, we do not recommend testing solely for circovirus,” the statement read. “Having a positive result for circovirus without knowing what, if any, other infections are present makes it difficult to interpret the results and develop an effective treatment plan.”

The source of dog circovirus is still unknown. “We don’t know exactly where it comes from,” acknowledges Dr. Roger K. Maes, virology section chief at MSU-DCPAH. “If you don’t look for it, you don’t find it; you have to have some incentive to look for it, such as the presence of diarrhea or vasculitis.

“Retrospective serological surveys will show when this virus first infected dogs,” Maes continues. “When we conducted our own analysis of old cases in which we thought circovirus could have played a role, we found circovirus present in cases from as early as 2007. If I were to guess, I would say some form of this virus has existed in dogs for a long time.”

Researchers are also trying to answer another key question—whether dog circovirus is dependent on the presence of another pathogen. “We don’t know whether the circovirus can cause disease on its own,” explains Dr. Matti Kiupel, anatomic pathology section chief at MSU-DCPAH. “There is some evidence that dogs infected with circovirus and another virus are at much higher risk of developing disease than dogs infected with circovirus only.”

Preventing Circovirus in Dogs

According to the AVMA, there’s no indication that dog owners should stop bringing their pets to kennels or doggie day care facilities to prevent their dogs from getting infected with the virus. Owners of such facilities should continue to take common sense measures to keep canine clients healthy by keeping sick dogs separate from healthy dogs; regularly cleaning and disinfecting all dog areas; monitoring all dogs for signs of illness; and immediately reporting any signs of illness to the dog’s owner, the AVMA advises in its fact sheet. In addition, there’s no evidence that circovirus can be transmitted to humans from their dog, AVMA states.

Dog circovirus does not generally pose a significant threat, Kiupel assures. “Would I go out and screen every dog for circovirus? Absolutely not,” he says. “There needs to be a clinical indication such as diarrhea of unknown cause.”

Kiupel advises dog owners to take a common-sense approach to dog circovirus by keeping their pets’ vaccinations current for known pathogens. “Vaccines are not expensive compared to the cost of treatment and supportive care, and they give you peace of mind,” he points out.

Currently, there’s no vaccine specifically for dog circovirus, “but we don’t have any evidence that we need to be vaccinating dogs for this,” Kubiski says.