Are dogs susceptible to this virus?
- Yes…but…not very…maybe.
- Depends what you mean by ‘susceptible’.
- Nice and clear, eh?
There’s a difference between being infected and being sick. Yes, dogs can become infected. However, they don’t seem to be as susceptible as cats and it’s debatable whether they get sick (more on that below).
Regardless, it’s clear that the virus can infect dogs. This has been shown in experimental studies and through identification of infected pet dogs. A few different experimental studies have been performed, with similar overall results. In one small study, SARS-CoV-2 (the virus that causes COVID-19) was detected by PCR in experimentally infected dogs, but they could not isolate the virus (suggesting the virus was present at a low level and the dogs were probably not infectious). The dogs remained healthy but some developed antibodies against SARS-CoV-2, supporting the idea that they were truly infected. They did not pass to virus to dogs with which they were co-housed. So, some or all of the exposed dogs got infected (the virus replicated in them for a while) but none got sick and they were probably not able to infect others.
Another experimental study yielded similar results….dogs could be infected and mount an antibody response, but didn’t get sick and were probably not infectious.
How often do dogs get infected?
We don’t know. Surveillance has been limited so the scope of human-dog transmission isn’t clear. The most organized approach to this was in Hong Kong, early in the pandemic. There, they offered to take pets from COVID-positive households into quarantine and test them. They identified the virus in nasal, oral and rectal swabs from 2/15 dogs that were quarantined initially. Neither had signs of infection, both developed antibodies to the virus and gene sequencing of the viruses from the dogs showed that they had the same viruses as their respective owners. Of particular note was the ability to isolate live virus from the dog. That suggests the dog could have been infectious.
Other study has been limited, in large part because it’s a logistical challenge to sample dogs in households with infected people during their isolation period. One small study in Spain didn’t detect the virus in 12 exposed dogs. An investigation of pets from a cluster of infected and exposed vet students didn’t find the virus in any of 12 tested dogs, although it wasn’t clear how many were actually exposed to an infected person. A study from Italy reported no detection of the virus in 64 dogs from households with previous human COVID infections, including 3 dogs that had respiratory disease.
Our initial study didn’t find it in any of 18 dogs (more to come on the expanded version).
However, there are numerous reports of individual infected dogs from different countries. In the US, ~23 infected dogs have been reported so far. That’s not a lot in the context of the dog population. But, not many dogs have been tested. Further, testing has focused on looking for the virus by PCR. That will underestimate infections because there’s a short window of time when you can get a positive PCR result from an infected dog. Dogs seem to only shed the virus for a few days after infection, so sampling dogs in infected households runs the risk of a lot of false negatives simply based on the timing of sampling.
Studies looking at antibodies will be more informative (if the tests are accurate) since detection of antibodies indicates infection in the past. Unlike our PCR-based surveillance, we don’t have to get into the household right at the time of human illness. We can test dogs later to see if they were infected.
Not a lot has been reported yet. A study in Italy found antibodies in 3.4% of dogs; 6/47 (14%) of dogs from known positive households, 1/7 (14%) from households of suspected cases and 2/133 (1.5%) of dogs from other households. Whether the 1.5% prevalence in other dogs is from dogs that were infected by owners that were never diagnosed or represents the false positive rate of the test isn’t clear. A French study found antibodies in 2/13 (15%) of exposed dogs and 0/22 dogs from households without known COVID-19. Those results are similar to our 20% (2/10) prevalence in positive households here so far. Obviously, we need to test a lot more dogs to get better info…that’s still underway.
Do dogs get sick?
That’s still unclear. I’d say that evidence is still far from convincing. There are a few poorly documented reports of sick dogs, but the question that has been largely unanswered with those is “did they have COVID-19 or were they sick with something else and also happened to have been infected by this virus?”. My guess is that disease is rare but not impossible.
Can dogs infect other animals or people?
Probably not, but that’s unclear too. Dogs are likely much lower risk that cats. The fact that virus was isolated from a dog raises concern, since if there was live virus in the dog’s nose, you have to assume there was some risk of exposure to in-contact individuals. Whether it was enough to actually infect someone is completely unknown. Lack of transmission in experimental models isn’t a guarantee (artificial environment, very small numbers) but provides more support of limited risk.
Overall, I’d say the risk is very low. I don’t think we can say it’s zero but I think it’s unlikely that a dog would pose a realistic risk.
That said, why chance it? If a dog is infected or at risk of being infected (living in a positive household) it should be kept away from other people and dogs. Dogs interact nose-to-nose and nose-to-bum a lot, and we have a lot of contact with their faces. We’ve seen other respiratory viruses transmission between neighbouring dogs through fence-line contact, so keeping exposed dogs under control and away from others is reasonable.
Could dogs be an important reservoir of the virus once it’s controlled in people?
No. Dogs are not susceptible enough to the virus. For dogs to be a reservoir, they’d have to be able to keep spreading it dog-to-dog. That’s not going to happen because of the low susceptibility and short shedding time. You’d need a very large number of dogs in regular close contact to even begin to get a risk. That’s not realistic here.
Could dogs be a bridge to wildlife?
Probably not…or at least it’s much less likely than cats. Their low susceptibility, short period of infection, limited (if any) infectivity and limited direct contact with wildlife mean the odds of them being infected by their owners then infecting wildlife are pretty negligible.
So, we shouldn’t worry about COVID in dogs?
But, we should pay attention.
What should be done with dogs?
Same as for cats…(see the cat synopsis for more details)
- If you are infected, try to stay away from animals…all animals…human and otherwise.
- If your dog has been exposed, keep it inside and away from others.
- Ultimately, dogs are part of the family so if your family is being isolated, the dog should be part of that.
Relax. This is almost exclusively a human virus. With a modicum of common sense, the risk posed from pets approaches zero.