July 6, 2020
Since the novel coronavirus that causes COVID-19 emerged in December 2019, scientists and veterinarians have struggled to understand its relationship to animals.
Most scientists now agree that the virus originated in bats, and probably passed through another species before infecting the first humans. Diseases that spread from animals to people are called zoonotic, and they are actually a lot more common than you think. Rabies, Ebola, and lyme disease are common examples, and more than 3 out of 4 emerging infectious diseases are zoonotic. Zoonotic diseases make this jump whenever humans are in close proximity to animals. As human populations grow and expand, and climate change forces animals to adapt, the possibility of new diseases is greater than ever.
Initially, scientists thought animals would not be susceptible to infection from humans. That all changed when two dogs and a cat in Hong Kong, living with humans infected with the virus tested positive. Since then, fewer than 20 pets have tested positive globally, all in homes with infected humans. With over ten million cases in people, this means that pets are at least somewhat resistant, and there is no evidence that pets play any role in transmission of the virus.
Based on laboratory studies, we also know that ferrets, Syrian hamsters, and cats may serve as “animal models” of human infection. This means that they potentially can become infected and transmit the virus to one another, as occurs in people. This is important because these animal models may be critical to understanding the virus and developing treatments and vaccines. At the Zoo, we assumed that primates, closely related to humans, would be susceptible, as they are to many human diseases including the common cold and the flu.
Since ferrets had already proven to be susceptible, we had also assumed that otters and red pandas may be similarly susceptible as they are genetically related. When a tiger, and later lions, at the Bronx Zoo became infected by an asymptomatic zookeeper in early April, it changed everything, and required us to implement the same safeguards that have been implemented to prevent spread between people – universal face coverings for staff working near the animals, a smaller social bubble through limiting staff involved with each animal, and physical distancing whenever possible. Outbreaks at mink farms in Europe in April and May, presumably initiated by infected caregivers, have also shown us that some animals are susceptible to the virus and can transmit it, highlighting our need to remain vigilant about the precautions for the animals and the staff.
So, those are the animals that we consider at highest risk based on infections in those species or in their close relatives. It appears, though, that all mammals may have some risk of COVID-19, and as in people, there are still many more questions than answers. While we have phased some of our safeguards out, similar to the phased re-opening, many are here to stay as we create a new “normal” behind the scenes at the Zoo until we understand more about this virus. The key to keeping our animals healthy is, as it always has been, keeping our community and staff healthy. That’s why your participation in the public health activities like wearing face coverings and physically distancing are so important. We are excited to welcome you back, safely. We can’t wait to see you, and your cool animal mask, at your next Zoo visit!
– Dr. Louis DiVincenti, Assistant Zoo Director – Animal Care and Conservation
*Banner photo by Wayne Smith