Dogs and coronavirus
We may have asked ourselves whether COVID-19 is an exclusively human disease.
Before getting into it we should be aware that coronaviruses are a virus family able to infect several animal species. They usually infect one species and eventually when 2 different species are living or interacting close together, they can jump from one to the other.
It is believed that the virus causing the disease COVID-19, named SARS CoV-2, jumped to humans from a mammal reservoir, probably bats (the exact link is still unknown).
Viruses usually adapt within a species and as an evolutionary strategy and survival, they go from one individual to the next in an endless chain of contagion. They learn how to infect as many individuals from one species as possible and adapt to that specific host internal environment. When a given virus gets into the body of a different species it is unlikely that it will thrive in the new host. That seems to be the case with the SARS CoV-2.
So, could dogs contract COVID 19?
There is one report of a dog in Hong Kong that got infected from his COVID-19 positive owner. The dog happened to be a cute Pomeranian breed dog. He was blood tested on March 3rd 2020 and got a negative result. At the end of the month, he was tested and found positive with the very specific test RT-PCR. There can be at least 2 interpretations for these findings. One is that the initial test could not detect antibodies because the virus was just in the early replication steps and antibodies were still not being actively formed and released to the dog’s blood at the time of sampling. Considering the dog was positive for RT-PCR later, means the virus was actually in his body. And here comes the second possibility: the dog was probably having a mild infection with a low generation of antibodies. This is one of the conclusions driven by scientists and would mean that SARS CoV-2 can jump from humans to dogs but cause very mild infection in our best friends.
What domestic animals are affected by coronavirus diseases?
Scientists have done experiments in which SARS CoV-2 (human virus) is placed in the nose of animals and the behavior of the virus followed afterward. These experiments have been done to know whether animals can be part of the transmission chains of the SARS CoV-2 and possible development of COVID-19 in animals.
From virus inoculation experiments in which human virus SARS CoV-2 was inoculated in the nose of animals, we know that ferrets and cats are highly susceptible to become infected by the virus.
The severity of the disease is higher in young cats because the upper and lower respiratory tract is massively affected while in ferrets, for not yet understood reasons only the upper respiratory tract is infected by SARS CoV-2.
The same study showed that dogs have low susceptibility to this specific virus. No RNA or viruses were found in any organ of dogs inoculated 2 days before. Antibodies against SARS CoV-2 were found on only 50% of the dogs inoculated and none in healthy dogs that were in contact with them. This means that if dogs are infected they will have a very mild infection because even though their body gets in contact with the virus and their immune system produces antibodies, they don’t get sick and the virus does not seem to spread from one dog to another.
So, it seems dogs cannot contract COVID 19, cats could get very sick if they are young (and probably but not yet proven, infect humans) while ferrets will get a kind of flu but not pneumonia. Cats can get the virus from a human but there is no evidence that cats can spread the virus to humans.
Can dogs get coronavirus?
In summary, human-adapted SARS CoV-2 is just not compatible with dogs. But dogs have been affected by canine coronavirus since long.
Actually, some coronaviruses attack laboratory and domestic animals like mice, rats, chickens, turkeys, pigs, cattle, cats, and dogs in a specific manner.
The first recorded coronavirus attack on dogs occurred during the early 1970s in military dog kennels in Germany. This particular virus did not thrive in the respiratory system but on the digestive tract instead, producing diarrhea as the main symptom.
Dog coronavirus is designated CCov (the first letter “C” after “Canine”). This first strain identified in Germany in 1971 was named CCov strain 1-71.
Several outbreaks followed in the years to come. Since then, CCov is widely spread in many countries, in dog kennels and shelters where dogs are close to each other and can easily spread the virus among them. Thus, the disease can be very infectious and spread quickly in closely packed dogs, but the mortality is low. However, this viral disease can be fatal when combined with the presence of <canine parvovirus (CPV-2)> or other viruses like <canine adenovirus type 1> or <canine distemper virus>.
CCov can be transmitted through the feces because the virus has a digestive tract tropism (the virus just loves that place). Nevertheless, the dog coronavirus can be found in other organs like tonsils, liver, and lungs without producing damage on those locations.
Through the years coronaviruses, in general, can mutate (point random changes in their nucleic acid -RNA- sequence) or recombine their RNA (a kind of shuffling of the virus genetic material). This means that now and then, new variants arise that can be potentially dangerous or pathogenic.
These are some examples of this:
- An outbreak by a hypervirulent gastrointestinal CCov strain (CCov type II, strain BGF10) was reported in the UK in 2004
- Fatal gastroenteritis by CCov in pups (2005, WA, USA)
- Fatal gastroenteritis by CCov (2007, Sweden)
- Highly virulent fatal disease in pups (Italy 2005) by CCov strains (CCov type II, strain CB/05) attacking lungs, liver, spleen, kidneys and gastrointestinal tract that have been called pantropic CCov disease
There also CCov viruses infecting and damaging the respiratory tract of dogs. The first reported case occurred in a kennel in the UK in 2003. This produces a mild respiratory disease in dogs and has been designated RCCov (“R” after “respiratory”, “C” after canine). Interestingly, this RCCov is not only related to CCov strains affecting the digestive system but also to cattle and human strains, suggesting shifts between species. Viruses evolve and we should be
Genome changes associated with pathogenic changes on the of CCov and coronaviruses, in general, occur once in a while. Viruses are forced intracellular parasites. To infect a dog, they require to enter the host cells. We should be increasingly prepared to face the threats of emerging viruses. That includes preventive measures as vaccinations and new therapies. Coronaviruses and other animal viruses are serious threats and will continue to appear producing new outbreaks in the future.
Please leave a comment if you would like more information on any of these topics or just to give your opinion.
In a future post, we will discuss the <anatomy and mode of operation of coronaviruses>, how they manage to infect the body of a pet, symptoms, and preventive measures.