Cats, Dogs & the New Corona Virus: Making Sense of What We Know So Far
There’s a whirlwind of information circulating about whether cats or dogs can contract Covid-19. This comprehensive article makes sense of that information — whilst reiterating why the public should not panic.
As Covid-19 swept across China, bringing bustling cities to a standstill in a matter of weeks, disturbing reports began to emerge from the country about the mass culling and abandonment of pets, borne of fears that they might become infected with the new Corona virus.
Multiple western media outlets reported that dogs and cats had been thrown from the windows of apartment buildings in Shanghai by their quarantined occupants. CNN re-published claims made on Chinese social media about stray dogs being buried alive in the country’s inner-Mongolian region. The BBC covered the struggle of animal rescuers on the ground in Wuhan Province, the birthplace of Covid-19, as they grappled with a wave of starving pets - some separated from their owners by travel restrictions, others deliberately abandoned.
When the virus spread, gaining a foothold in 209 territories, similar tales of violence against animals began to drift out of Lebanon, Egypt, and countries where the culling of strays is generally already commonplace.
Fortunately, at the London-based cat charity where I volunteer, we’ve yet to see evidence of any growing hysteria - quite the opposite, in fact; the charity has been overwhelmed with fostering enquiries from families hoping to fill the void created by the lockdown.
Nevertheless, these reports highlight the danger that widespread panic could represent for dogs and cats. Although cultural attitudes in the west towards pets are gentler and more sentimental than that in some parts of the world, they are far, far from perfect.
Rescue centres are already beleaguered with animals surrendered or abandoned for arbitrary reasons; a new baby, a new boyfriend, a new house. The result is hundreds of thousands of cats and dogs euthanised each year because there are simply not enough adoptive homes. Therefore, should fears about cats and dogs transmitting Covid-19 increase, there is every possibility that rescue centres the world over will see a large influx, and animals will pay with their lives. In a pandemic that was born of our mistreatment of animals - the trade in wildlife - that is especially frustrating.
So, whilst I have been talking to veterinary virologists and epidemiologists in recent weeks to clarify some of the misconceptions about the new Corona virus and its relationship with dogs and cats, I'm aware that in trying to do so, I walk a knife-edge; balancing being accurate with discouraging unwarranted panic.
Recently, the BBC failed spectacularly at striking this balance in their coverage of a press release made by the British Veterinary Association. The BVA statement suggested that cats from households with infected persons should be kept inside, if possible, for a period of isolation, but the BBC’s article, particularly its headline, was interpreted by cat owners to mean that all cats should be kept inside, sparking a furor of anxiety; the BVA were forced to issue a clarification.
The truth about companion animals and how the virus might affect them doesn’t warrant panic of this kind, but it is nuanced, and nuance is not always easily-digestible to the public. Sweeping absolutes, sensationalism, and broad generalisations; these are the stuff of viral internet content, if you’ll excuse the pun. So, before I begin, I beg you; let logic and compassion guide you when making decisions about your pets in this crisis, not panic, and not short-sighted, over-zealous self-preservationism. Had we strove for this from the offset in our dealings with animals, perhaps the human race wouldn’t be in the position it is today.
So, Can Cats and Dogs Catch Covid-19?
There are some isolated cases of dogs and cats testing positive for Covid-19, believed to be the result of humans transmitting the virus to their pets. There are no known cases of pets transmitting the virus to humans, and no evidence thus far that this is possible. The early infections in China were all traced back to human-to-human transmission, and our species alone are undoubtedly the biggest, most significant source of the infection.
This is the most salient point in assessing the risk posed by dogs and cats in the pandemic.
The second is how few dogs and cats have tested positive for Covid-19 so far, despite substantial monitoring. For example, in March, IDEXX, a leading veterinary diagnostic company, tested thousands of samples from dogs and cats for the new Corona virus, to no positive results.
Given the explosive, global scale of the virus, and the close contact that many people have with their pets, this suggests that it is rare for humans to infect companion animals, and that they are not a meaningful factor in its spread. Infectious disease specialist and Dean of Cambridge Vet School, Prof. James Wood, reinforced this theory:
“If cats and dogs were playing any role in transmission, given that millions of people have now caught the virus, I would expect this to have been identified already. It seems clear that dogs and cats have not played a ‘significant’ role in transmission around the world. It is more or less impossible to rule out the chance that any individual species could never transmit to another species. Rather, all the evidence so far is that cats and dogs (and tigers) have been victims, not perpetrators.”
Because of physiological differences, some animals may be more susceptible to a specific virus than others - how susceptible they are may depend on factors like how well that virus binds to the proteins in each species’ cells.
So, despite the virus being present in their bodies, some species may never develop enough of an infection, or ‘viral load’, to experience symptoms or transmit the virus to other animals. This may explain why the first dog recorded with Covid-19 tested only ‘weakly positive’. Such animals are considered ‘dead-end hosts’ in epidemiology terms, meaning they are irrelevant in the context of viral transmission.
It’s worth noting that Covid-19 tests for animals are conducted by veterinary laboratories, so their availability is unrelated to the availability of tests for humans. This is why Bengal tigers at the Bronx Zoo were able to get tested, despite a shortage of testing for much of the human population.
The small number of cats who have tested positive for Covid-19 include tigers at the Bronx Zoo, a cat in Belgium, and sadly, a small group of cats who were deliberately infected at the Harbin Veterinary Research Institute in China.
Unlike dogs, some cats who have tested positive for Covid-19 have exhibited symptoms of the virus, such as respiratory distress and diarrhea. However, the cat in Belgium recovered after twelve days, and the Bronx tigers are not considered in serious condition. Both are believed to have contracted the virus from contact with infected people.
Of the five cats who were deliberately exposed to Covid-19 in the Harbin Institute experiments in China, none showed symptoms, despite two subsequently testing positive for the virus. Three of the exposed cats were put in close proximity to three healthy cats, but only one of the healthy cats became ill as a result of this contact. This indicates that cats can transmit the virus to other cats through droplets, but not necessarily quickly or easily - “It suggests the virus may not be highly transmissible in cats”, said the chief researcher in the experiment.
Another important factor to consider here is the viral load, which describes the quantity of virus or viral particles that enter the body.
Scientists have theorized that a large viral load may result in a more severe infection of Covid-19, explaining why some people have died of the virus despite being young and having no pre-existing conditions. To put it in simple terms, an infected person sneezing in your face may result in you receiving a larger viral load than say, if you touched a surface that an infected person had previously sneezed on, and then touched your face.
The cats at the Chinese research centre were directly infected with large doses of the virus. Such a significant viral load may be unlikely to occur outside of a laboratory setting, in a cat’s normal day-to-day interactions with people. A smaller, naturally-occuring viral load may decrease the cat’s ability to pass the virus to other cats - after all, we know that despite millions of people being infected with Covid-19 globally, there are just a few recorded cases of feline infection.
The study also only involved a small number of cats, and has yet to be peer reviewed. It is not conclusive, and does not suggest in any way that cats can pass the virus to humans, only to each other in some conditions. Any measures arising from this research, at this point, are purely precautionary, undertaken ‘just in case’ as we learn more about the virus. This includes the BVA’s recent suggestion that cats living with infected persons should be kept inside, if possible - due to the very slim chance that they may catch the virus from their owners, and subsequently infect other cats.
Both cats and ferrets also previously proved susceptible to infection from SARS, Severe Acute Respiratory Syndrome, an earlier, related strain of Corona virus effecting the respiratory system. Similarly, there was no indication that they played a significant role in the spread of the virus to humans.
There are two recorded cases of dogs testing positive for Covid-19 as a result of contact with an infected human, a 17-year old Pomeranian and a German Shepherd Dog, both in Hong Kong. The German Shepherd dog lived with another, mixed-breed dog who tested negative for the virus.
Neither of the infected dogs showed any symptoms and only weak levels of the virus were found in the Pomeranian’s system. It later died, but there is no evidence that this was related to Covid-19 - its advanced age, and the stress of being quarantined, are two more likely factors.
At the Harbin Veterinary Research Institute in China where experiments were conducted on cats, five dogs were also given large doses of Covid-19. Traces of the virus were found in their feces after the dose was administered, but none tested positive for the virus. At present, it is theorized that dogs may be ‘dead-end hosts’ for Covid-19, unable to sustain large enough quantities of it in their systems to pass it on to any other animal, or to experience symptoms.
What about other types of Corona Virus - like Canine and Feline Corona Virus?
Before Corona virus became a term familiar to the world, it was familiar to animal rescue workers and veterinary professionals. This is because of Canine Corona virus (CCoV) which can manifest as a digestive disorder, and Feline Corona virus (FCoV), which can sometimes develop into a deadly disease called feline infectious peritonitis, or FIP.
There is currently an image circulating on social media that seems to suggest that because cats and dogs are susceptible to FCoV and CCoV respectively, they are not able to be infected with Covid-19. However, whilst all of these viruses are Corona viruses - a term describing a family of viruses - they are otherwise unrelated. They are all separate diseases, and unfortunately, being susceptible to FIP does not negate a cat from also being susceptible to Covid-19. It is, by definition, a zoonotic virus, with origins in animals - therefore we can expect it to be potentially transmittable to more than one species.
“The other coronaviruses of domestic animals bear no relationship with the virus causing COVID19 – being part of the same virus family is just like saying that you are related to a random fellow human being in the next door city”, says Professor James Wood of this topic.
What Is the Role of Bats and Pangolins?
Different animals can act as different types of hosts for viruses. As mentioned previously, a ‘dead-end host’ is an animal that can contract the virus, but cannot sustain large enough quantities in its system to transmit it to other organisms.
‘Reservoir’ or intermediary hosts play a different role in viral transmission, one that is quite contested in academia. In extremely simplified terms, they are animals that harbour viruses in their bodies but are usually unaffected by them, not experiencing any symptoms. This is because they are not the target host of a virus, but merely a means of storing it for transmission to another animal, who is the intended target. All of the disease specialists that I spoke to said that because so few dogs and cats have been found to be infected, they probably make poor viral reservoirs for Covid-19.
For example, in the case of SARS, bats passed some variant of the virus to Palm Civets, who acted as reservoirs for the disease. When humans ate those same Palm Civets or came into contact with their bodily fluids at wildlife markets, we became the target host for the virus. With Covid-19, a similar chain of transmission may have occurred, only with bats and Pangolins. Once the virus has been transmitted to the intended host, these reservoirs no longer play much of a role in its ongoing spread.
The likelihood of viral pathogens successfully making species jumps like this is very rare, however it increases tenfold when we put ourselves in close contact with wildlife that we are unlikely to otherwise encounter. We effectively offer ourselves up as a potential target in the cycle of transmission when we harvest exotic species for food, medicine, the pet trade, or encroach on their habitats. In the rare instances that viruses do successfully cross that species barrier, we prove to be the ideal hosts, our capacity for international travel and commerce spreading pathogens far and wide.
As David Quammen, author of Spillover: Animal Infections and the Next Human Pandemic said in a 2012 interview; “Now viruses don't have intentions. They don't make choices. But given opportunities, they will spill over into new hosts. And when they spill over into humans, they've won the jackpot, they've won the sweepstakes.”
What Can We Do to Protect Our Pets Against These (Small) Risks?
As we've established, if you become infected with Covid-19, you're unlikely to pass it to your cat or dog, and on the seemingly slim chance that this transmission does occur, it is not a death sentence and they may not even exhibit symptoms, particularly dogs. Nevertheless, because our understanding of this disease is still evolving, acting with caution wherever possible is advisable. If you believe you have Covid-19, then keep interaction with your pets minimal. Strictly avoid kissing them, touching them unless necessary and only then with clean hands, and prepare their food with freshly washed hands. As per the BVA's recent recommendation, if your household is self-isolating due to suspected Covid-19, then isolate your cat along with the rest of the family - but only if this is a practical option and doesn't cause them considerable stress.
This is to protect against the small possibility that your cat will catch the new Corona virus from infected family members and spread it to cats that they encounter outside. Droplets from the virus can also accumulate on an animal's fur just as they can accumulate on surfaces and furnishings. Though the virus is unlikely to survive for long periods on fur, it is still possible for a healthy person to be exposed to those infectious droplets by say, stroking your cat as they pass it in the street, and then touching their face.
The first line of defense against the growing climate of panic seems to be to deny that there are any legitimate cases of cats or dogs contracting the virus, to brandish such reports as 'fake news'. I don't think this is effective. Rather than trying to deny or hide information from the public, I think it's far more effective to put that information in its proper context.
Because in context, there is no reason for the public to panic about pets becoming infected with Covid-19. Yes, there are cases of cats and dogs contracting it, but these are extremely rare. Given that there are nearly two million infected humans globally, and that we humans are regularly in close contact with our pets, it is logical to assume that this virus does not transmit easily from humans to dogs and cats. In the case of dogs, there is no evidence that they can transmit the virus, full stop, and where cats are concerned, there is some evidence that it is difficult for them to even pass it to one another.
We are still only months into investigating this new virus, and we may not ever fully understand its behaviour and implications; there is still much we don’t know about SARS, first seen in the early 2000’s. But that some questions linger indefinitely, does not justify bludgeoning street dogs to death, flooding rescue centres with family pets or slaughtering colonies of bats. Such actions are borne of the same attitude that has seen animals housed in squalid and inhumane conditions at wildlife markets across the world - conditions perfect for nurturing the next viral outbreak. Disregarding the rights of animals on the most basic level to live peacefully and free from harmful human interference is part of the problem here, not the solution.