A few months into the global COVID-19 pandemic there is growing knowledge about the relationship between the virus and animals.
In a recent column, I discussed how wild bats were the likely origins of the virus and how future spill-over events may be prevented by ending the global wildlife trade.
Virus origins aside, there have been no confirmed cases of animals spreading the virus to people. But there are a growing number of reports of people spreading the virus to their animals.
So far, our pets have been the most commonly infected species outside of experimental laboratory studies. There are reports of a few dogs and cats becoming infected with the virus when in close contact with infected people. In these situations, people likely passed the virus to their pets. There are no reports of pets passing the virus into people.
Cats can develop respiratory illness when infected with the virus, while the situation in dogs is less clear. One cat each in Belgium, Hong Kong and New York have tested positive so far. These cats developed clinical signs consistent with respiratory illness that included coughing, wheezing, difficult and rapid breathing, as well as appetite loss.
A dog in South Carolina that tested positive for the coronavirus had a cough and appetite loss, while two positive dogs in Hong Kong showed no signs of illness.
A key feature of these pet infections is that they are almost always in households with infected people, and other pets in the house are not affected. This suggests individual animals may differ in terms of susceptibility to infection, or different levels of exposure can exist within the same home.
These few cases in pets are likely the tip of the iceberg. The lack of illness in dogs means they are unlikely to be tested.
For cats, clinical signs of infection with the COVID-19 virus are similar to common infections in cats and are not severe. Cats with colds are far more likely to be ill with feline herpes virus and calicivirus. The similarity of clinical signs between COVID-19 and other common respiratory tract infections in cats, combined with the relatively mild illnesses, means cats are unlikely to be seen by a veterinarian and even less likely to be tested.
A report out of France involves 20 veterinary student roommates and their pets. In this instance, none of the 12 dogs or nine cats tested positive for the virus even though 13 of the 20 students likely had COVID-19. This suggests that pets probably have some resistance to infection and that very close contact between infected people and pets is necessary for the virus to spread.
It might also be that dogs and cats need to be exposed to a high dose of virus to get infected. Researchers will probably undertake studies to further explore pet exposure in the future.
An outbreak of COVID-19 among five tigers and three lions at the Bronx Zoo suggests that most likely many cat species are susceptible to this infection. In this case, it was most probable that a human spread the virus to the zoo cats.
In research settings, ferrets are a popular laboratory animal in which to study human respiratory viruses. Preliminary experimental studies show that ferrets and hamsters are susceptible to infection. So far, there are no reports of pet ferrets or hamsters becoming infected, but it is possible given these laboratory results.
So far, it seems as though domestic livestock do not become infected or transmit the virus. In particular, laboratory experiments show that the virus does not transmit to ducks, chickens or pigs. Cattle and horses also do not appear to be susceptible to infection. Further studies are necessary to fully understand the risk to domestic livestock.
There are growing concerns that endangered species may be severely impacted by COVID-19. Indirectly, many parks and conservation initiatives depend on tourism, which has stopped for the time being. Additionally, some animals may be susceptible to infection with unknown but potentially severe outcomes. These endangered species include great apes, and closer to home, the black-footed ferret.
There are substantial knowledge gaps in terms of how COVID-19 affects animals. However, some general guidelines should be followed to reduce the chance of transmission.
If owners contact someone known to have the COVID-19 virus or show symptoms consistent with the disease, they should take steps to minimize contact with their animals. I know cats aren’t always the best at social distancing. But people who are sick should avoid close contact with their pets and livestock to reduce the chance of spreading the infection to them.
This includes frequent hand washing, avoiding coughing near the animal and if possible, have someone else in the household manage husbandry until the person is recovered.
Although the chance is small, pets might be able to spread the virus so it is important to physically distance pets from each other. If possible, keep your pets inside and avoid allowing them to interact with other pets if outdoors.
Dr. Jamie Rothenburger, DVM, MVetSc,PhD, DACVP, is a veterinarian who practices pathology and is an assistant professor at the University of Calgary’s Faculty of Veterinary Medicine. Twitter: @JRothenburger