Circovirus in dogs came into the national spotlight in 2013 as several dogs in Michigan, Ohio and California possibly became ill or died from this newly discovered virus. Companion dog caregivers were justifiably concerned.
Bear in mind that the sickened dogs did not cause the discovery of this virus. Dog circovirus was actually discovered a year earlier in 2012 because a study was testing blood samples for new or undiscovered canine viruses. That study by Kapoor et al. did not list circovirus-related symptoms in dogs, because they did not know what the symptoms were. They simply found the virus.
No one knows how long dog circovirus has been around. A Michigan State University research team stated in 2013 that their retrospective analysis demonstrated circovirus present in cases from as early as 2007. They also postulated that they would likely find circovirus in even older cases.
As to the dogs that fell ill in 2013, we do not know the exact numbers that had circovirus. In fact, some of the ill dogs might not have had circovirus at all, but demonstrated symptoms that may have been similar to what other confirmed dog circovirus cases presented.
In 2013, the cart was clearly placed before the horse regarding dog circovirus. Think about it: we haven’t heard much about dog circovirus since 2013.
However, circoviruses are no joke…and dogs can develop serious illness – more on that later.
Pigs and birds also harbor circovirus strains specific to their species. Foxes in the United Kingdom (UK) also have a documented strain. The difference is how the circovirus manifests in the body.
In pigs, porcine circovirus Type 1 is widespread, but is considered nonpathogenic. Porcine circovirus Type 2 is strongly associated with the occurrence of a postweaning multisystemic wasting syndrome and appears to have an association with porcine dermatitis and nephropathy (kidney) syndrome, porcine respiratory disease complex, and occasionally reproductive failure.
Bird circovirus is known as “beak and feather disease”. Birds with the disease may not show any symptoms for weeks or years. The first visible clinical sign is dead or abnormally formed feathers. Once signs are seen, most birds die from secondary infections within 6-12 months.
Foxes in the UK infected with fox circovirus may develop meningoencephalitis, a neurological disorder. According to the UK researchers, clinical data indicated that 77% of circovirus-positive foxes had signs of neurologic disease, compared with only 47% of circovirus-negative foxes. Fox circovirus was detected in 2 out of 4 foxes with neurologic disease, but not in the brain tissues of 2 foxes without disease. They determined that circoviruses commonly cause systemic infections in wild foxes and can be detected in the brains of foxes with neurologic disease.
As related above, not all circovirus positive foxes presented symptoms.
This is where circovirus gets tricky – and it’s tricky in dogs as well.
Circovirus in Dogs
Circovirus is a virus that affects the gastrointestinal tract first. The first symptoms are diarrhea and vomiting. At this time, we believe that if the disease progresses, it leads to vasculitis based on the limited evidence we have thus far.
The first research study in 2013 evolved by happenstance when a dog was admitted to University of California at Davis School of Veterinary Medicine for diarrhea and vomiting. Despite supportive and aggressive care, his condition was worsening and the overall prognosis was poor. His caregiver decided to have him put to rest and granted permission for routine autopsy. While this was very sad, the dog became a guardian angel for other dogs.
The team took the information his body imparted in several important directions. They collected 21 samples from dogs that had at least two of the same signs: vasculitis, hemorrhage, or granulomatous disease. Three of them dogs with compromised vascular function also had circovirus in their lymph nodes and spleens. While 18% of the cases might seem low, it gave the veterinarians a good basis to test dogs with unknown vasculitis for circovirus.
They also conducted a prevalence study and made three very important discoveries.
• Circovirus was detected in fecal samples from 14/204 healthy dogs.
• Circovirus was detected in fecal samples from 19/168 dogs with diarrhea.
This difference in prevalence was not significant: 6.9% vs. 11.3%, respectively.
However, what was significant was a co-infection, as 13 of the 19 dogs with diarrhea were co-infected with one or more other pathogens. This does not mean the co-infection is necessary for circovirus to thrive, but it gives us greater insight as to what research avenues to pursue.
Two more studies were published in 2016 that surveyed dogs in Northern California and Taiwan, respectively.
A study in Northern California considered the prevalence of several pathogens at three Northern California dog parks. They had the companion dog parents judge the feces of their dogs based on visual images and collect fecal samples. The prevalence of circovirus detected was 9% (27/300 dogs) – similar to that found in the 2013 study. This group determined, “The amplification of circovirus DNA from normal dogs and the lack of association with fecal score suggest that this virus might be nonpathogenic in many dogs.”
Researchers in Taiwan performed a similar prevalence study. They found that dogs with diarrhea were three times more likely to be circovirus positive than those deemed clinically healthy. In fact, their figures were surprisingly high. 58/207 (28%) of diarrheic dogs were circovirus positive. By contrast, only 12% (19/160) of non-diarrheic dogs were also circovirus positive.
The authors noted the differences to the 2013 study and determined that the diagnostic testing method and the geography played a part.
However, this study’s results were proportionate to the 2013 study in one regard. 43/58 (74.1 %) circovirus positive diarrheic dogs did not have additional co-infections. But, 12/15 were co-infected with canine parvovirus-2a and 2b. In the United States, the majority of dogs are vaccinated against parvovirus.
This study did not note if symptoms had advanced in dogs due to vasculitis.
Vaccines and Common Sense
Currently, a vaccine does not exist for circovirus in dogs. We have a lot to learn about the disease and a vaccine might not be efficacious. As well, we do not have evidence that the virus is mutating or becoming more dangerous.
At this point in time, the best thing to do is to prevent your companion dog from sniffing or eating another dog’s waste and always pick up after your dog.
Bexton, Steve et al. “Detection of Circovirus in Foxes with Meningoencephalitis, United Kingdom, 2009-2013”. Emerging Infectious Diseases vol. 21,7 (2015): 1205-8. doi: 10.3201/eid2107.150228. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4480402/.
“Circovirus.” Veterinary Diagnostic and Production Animal Medicine, Iowa State University College of Veterinary Medicine, http://www.vetmed.iastate.edu/vdpam/FSVD/swine/index-diseases/circovirus.
Hascall, K L et al. “Prevalence of Enteropathogens in Dogs Attending 3 Regional Dog Parks in Northern California”. Journal of Veterinary Internal Medicine vol. 30,6 (2016): 1838-1845, doi: 10.1111/jvim.14603. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5115183/.
Hsu, Han-Siang et al. “High detection rate of dog circovirus in diarrheal dogs”. BMC Veterinary Research vol. 12,1 116. 17 Jun. 2016, doi:10.1186/s12917-016-0722-8. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4912760/.
Kapoor, Amit et al. “Complete genome sequence of the first canine circovirus”. Journal of Virology vol. 86,12 (2012): 7018, doi: 10.1128/JVI.00791-12. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3393582/.
Li L, McGraw S, Zhu K, et al. “Circovirus in Tissues of Dogs with Vasculitis and Hemorrhage”. Emerging Infectious Diseases vol. 19,4 534-541, doi:10.3201/eid1904.121390. https://wwwnc.cdc.gov/eid/article/19/4/12-1390_article.