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Sep 12

Circovirus: A New Threat to Dogs

Unusual Virus Spreads in Ohio

The recent death of four dogs in Ohio has sparked concern about the spread of a new virus, which, until recently, had never been described in dogs. Four Ohio dogs died recently, and a virus new to dogs is suspected. The dogs were from more than one area of Ohio: 3 from the Cincinnati area and 1 from the Akron-Canton area. The veterinarians who treated one of the dogs that died also saw other dogs with similar symptoms that survived. The Ohio Department of Agriculture is investigating the outbreak.

Circoviruses Made an Interspecies Leap

Before now, circoviruses were known to infect fish, birds, and pigs, but not dogs. In fact, pigs were the only mammals circoviruses were known to infect before they were found in dogs. The circoviruses have apparently made an interspecies leap from one host to another. An article in Emerging Infectious Diseases (April 2013) describes the discovery of a circovirus that infects dogs (DogCV). In the article, Circovirus in Tissues of Dogs with Vasculitis and Hemorrhage, Linlin Li, et al, describe sequencing the viral DNA and comparing the sequence with other viruses in the circovirus family. They determined that DogCV is most closely related to the circoviruses that are known to infect pigs (PCVs) and more distantly related to those that infect fish and birds. This means that the DogCV likely evolved directly from the PCVs. It makes scientific sense that it is the PCVs that adapted to infect dogs. PCVs DNA are already adapted to a mammal (pigs), and thus adapting to another mammal (dogs) might require the least change.

What Are the Symptoms of Circovirus in Dogs?

  • Circovirus Symptoms

    • Vomiting
    • Bloody Diarrhea
    • Weight Loss
    • Lethargy

Circoviruses typically causes hemorrhaging, inflammation of the blood vessels, and immunosuppression. Symptoms an owner might notice include vomiting, bloody diarrhea, weight loss and lethargy. In other species (e.g., pigs) circoviruses often coincide with infection of other pathogens, but it is not known whether this is also true in dogs. If a dog is co-infected, the other pathogen might cause additional symptoms as well. In addition, other bacteria and viruses also cause some or all of these symptoms and circoviruses may not be involved in the illness at all. However, if your dog has  symptoms of a circovirus, do not hesitate to seek veterinary care. Your dog may receive potentially life-saving supportive care if it has this virus. Even if your dog does not have circovirus but is infected with a different pathogen, it likely still  needs treatment for these serious symptoms.

Dog Virus, Pig Virus–What’s the Difference?

You may ask, “If a virus can infect a pig, why is it news that it can infect a dog?” What a virus will infect, be it a dog, pig, human, plant. fungus, etc., varies greatly depending on the virus. Some viruses are specific to dogs just like some viruses are specific to humans. Other viruses are “generalists” and infect a wide variety of species.

The key is subtle differences between the different host species like pigs and dogs. Since viruses do not have cells or the machinery to replicate on their own, they must enter the host cell and use the host’s own cellular machinery to propagate. The different molecular interactions that take place between the virus and host are very specific. Imagine a lock and key. If the key doesn’t fit into the lock, the door doesn’t open. In the same way that differences between keys can be very subtle, very subtle differences between species can generate barriers to a virus’s ability to infect a new host.

If Circovirus Can Now Infect Dogs, What Changed?

The virus changed. All organisms have either DNA or RNA which serves as the blueprints for the molecules the organism will produce. Changes in the DNA (or RNA) sequence (mutations) create changes in the molecules produced. This is the mechanism of variation for all living organisms and viruses.

As mentioned above, viruses must enter a host cell to replicate. Most commonly, the virus enters the cell by “tricking” the cell into thinking it is a nutrient or other necessary molecule. Most nutrients taken up by cells are recognized by molecules (receptors) on the outside of the cells. Cells typically use receptors specific to a certain nutrient to accomplish this. Receptors on the outside of the cell recognize the molecules to be imported and facilitate transport across the cell membrane.

Viruses use this system to “hijack” one of these receptors and use it to gain entry to the cell. The virus changes in such a way that it can mimic the molecule the receptor was made to transport. If we again use the example of a lock and key, the virus has made a copy of the key, or at least enough of it to trigger the lock and open the door.

However, the same key that operates the pig lock may not operate the dog lock. If the virus changes yet again to accommodate a new species, the change may only need to be a slight one. The virus’s “key” could now fit the dog “lock” thus opening the door and allowing the virus to infect the dog.

How Can I Protect My Dog?

Currently, there is no vaccine for DogCV. However, the disease does not seem to be widespread across the US at this time. Dog owners should, as always, be aware of their dog’s health and watch for any symptoms that cause concern, including those for DogCV (vomiting, bloody diarrhea, weight loss, and lethargy). Dog owners in Ohio and the surrounding area should be especially vigilant. If your dog is ill, seek veterinary care and isolate it from other dogs until the cause of the illness can be determined.

“We feel obligated to make sure pet owners are aware this is happening…but we don’t want people to get too worried.”
–Erica Hawkins, Ohio Department of Agriculture

While DogCV is an emerging illness in dogs, dog owners should not panic, according to the communication director for the Ohio Department of Agriculture, Erica Hawkins. “We feel obligated to make sure pet owners are aware this is happening,” Hawkins said. “Supportive therapies can be helpful if started early enough. But we don’t want people to get too worried.” (As reported by the Columbus Dispatch September 10, 2013.)

About the Author

The author of this post has an M.S. in biochemistry and molecular biology. She has worked for 10+ years in a research lab that focuses on the evolution of viruses. Most of her work involved the evolution of genetic elements of certain bacteria and viruses that affect their transmissibility and biodiversity. She is also an avid dog lover.

 

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