A report from Hong Kong indicates that a dog has tested “weak positive” for the COVID-19 virus. The dog was tested because its owner has COVID-19, not because the dog was showing any signs of illness. Testing of pets is not routine in most areas, but it’s good to see it being considered and investigated.  However, we need to sort out what this test result actually means.

The test that is typically used for a virus like this is PCR (polymerase chain reaction), a molecular test that detects viral nucleic acids (DNA or RNA depending on the virus – RNA in the case of coronaviruses). This type of test can be very sensitive and pick up very small amounts of virus, live or dead. If the dog was living with an infected person, it’s possible that some live or dead virus from the owner could have transiently contaminated the dog’s nose or mouth (especially considering how dogs tend to interact with people and explore the environment).

The dog is being held in a shelter with no other animals and presumably being handled as infectious. Repeated testing is planned.

There are a few important questions at this point:

Is it a true positive for the COVID-19 virus?

  • Further testing might help figure this out. If they get more positive results on samples taken after the dog has been removed from the household (especially stronger positive results), that would be more supportive of a true infection, rather than transient contamination.

If the dog is positive, is it infectious to others?

  • Infected and infectious aren’t necessarily the same thing. It might be possible to have a very low grade infection but not shed enough virus to pose a risk to others. Further testing will help sort this out too.

Does the COVID-19 virus cause disease in dogs?

  • Viruses can sometimes infect a species but not cause disease. That’s good for that species, but if they’re able to shed the virus, it can create a new pool of infection for other species. I doubt this is the case with dogs and COVID-19 but it needs to be explored.

Overall, my concerns are still more about cats. Dogs will probably get investigated more because there are more pet dogs than cats in most regions, and people tend to seek healthcare for the dogs (or alternative caretakers if the owner is indisposed due to illness) quicker than for their cats. However, the genetic makeup of the virus suggests that cats are at greater risk of being infected if they are exposed (as with SARS). The situation, as with most aspects of COVID-19, is still very fluid; hopefully more information will come soon.