COVID-19 may cause heart inflammation in cats and dogs

• Researchers conducted a study to investigate whether there is a link between a spike in cardiac inflammation among cats and dogs and SARS-CoV-2.
• They found that the majority of pets studied had contracted SARS-CoV-2 shortly after it was either confirmed or suspected that their owners had the virus.
• The researchers conclude that pets can contract the B.1.1.7, or Alpha, variant of the virus. However, scientists will need to carry out more research to confirm how exactly it affects pets.

Several case reports have emerged worldwide about pets, especially cats and dogs, contracting SARS-CoV-2 from their owners.

Symptoms were mostly mild and included mild digestive and respiratory issues, such as cough, runny nose, and sneezing.

Despite large surges of SARS-CoV-2 cases in the United Kingdom since November 2020, thus far, there have been no reports of animals contracting the virus.

Tracking the transmission of SARS-CoV-2 to animals is vital for the safety of animals and for preventing the formation of viral reservoirs that could perpetuate the pandemic.

Recently, researchers from the U.K. and France recorded several cases of cats and dogs that seemed to have contracted SARS-CoV-2 from their owners, and developed symptoms of myocarditis, which is inflammation of the heart muscle.

“Our study reports the first cases of cats and dogs affected by the COVID-19 Alpha variant and highlights, more than ever, the risk that companion animals can [contract] SARS-CoV-2,” says Dr. Luca Ferasin, D.V.M., Ph.D., lead author of the study and head of Cardiology at The Ralph Veterinary Referral Centre (TRVRC) in the U.K.

“We also reported the atypical clinical manifestations characterized by severe heart abnormalities, which is a well-recognized complication in people affected by COVID-19 but has never [been] described in pets before. However, COVID-19 […] in pets remains a relatively rare condition and, based on our observations, it seems that the transmission occurs from humans to pets, rather than vice versa,” he adds.

The study appears in the journal VetRecord.

Acute myocarditis

Between December 2020 and February 2021, vets at TRVRC noticed an increase in cats and dogs with signs of acute myocarditis being admitted to their clinic.

Myocarditis accounted for 12.8% of their cardiology cases, compared with around 1.5% in the previous year.

Altogether, they diagnosed 26 cats and dogs with the condition between December 2020 and March 2021.

This, they observed, coincided with the peak of SARS-CoV-2 cases in the U.K., making them suspect a possible link. To investigate, they asked the owners of these pets whether they had symptoms of COVID-19 in the preceding weeks or whether they had tested positive for SARS-CoV-2 at any stage.

The researchers found that the majority of owners of these pets had contracted SARS-CoV-2 3–6 weeks prior to their pets’ illness. The vets decided to test the cats and dogs for the presence of the virus using molecular testing (PCR) and antibodies in their blood.

To do so, they collected blood, oro-nasopharyngeal, and rectal swabs from six cats and one dog with a diagnosis of suspected myocarditis following direct contact with people in their household with confirmed or suspected SARS-CoV-2. They also collected blood samples from two cats and two dogs during their recovery phase.

They sent the samples to the MIVEGEC laboratory at the University of Montpellier in France to undergo molecular testing (PCR) and testing for antibodies.

Following diagnosis, the vets noted that none of the 11 study animals with myocarditis developed influenza-like symptoms and that they all clinically improved within a few days of intensive care treatment. Further diagnostic tests did not reveal any alternative viral, bacterial, or other cause of their myocarditis.

Altogether, two cats and one dog tested positive on PCR tests, and two cats and one dog had developed antibodies against COVID-19.

The vets also noted that all of these pets tested positive for the Alpha variant of the virus, which was responsible for the sudden surge of SARS-CoV-2 cases in the U.K. between December 2020 and March 2021.

The findings match those from a recent case report from France that builds the evidence for an association between transmission of the Alpha variant to pets and the development of myocarditis.

Transmission from owner

“We believe that these dogs and cats [contracted SARS-CoV-2] from their owners, since they developed clinical signs a few weeks after their owners had symptoms of COVID-19 or tested positive for the presence of the virus,” Dr. Ferasin told Medical News Today.

“These pets all presented to our emergency service for sudden onset of weakness, loss of appetite, fainting due to underlying cardiac arrhythmias, and difficulty breathing due to the presence of fluid in their lungs secondary to their heart condition — congestive heart failure.”

MNT also spoke with Dr. Margaret Hosie, professor of comparative virology at the University of Glasgow in the U.K., who was not involved in the study. She said:

“When SARS-CoV-2 infects a person, it binds the ACE-2 receptor to gain cell entry and to initiate the infection. So in species in which the ACE-2 molecule is similar to the molecule in humans, it is possible that the virus might also be [transmissible to] that species.”

“This is the case for cats and dogs, as their ACE-2 receptor molecule shows high sequence homology with the human counterpart,” she explained.

“Since ACE-2 is widespread in the body, SARS-CoV-2 infects many organs, such as the heart and lungs. In humans and — as the receptor distribution in animals is similar — we might expect to see similar clinical signs in infected animals. However, to date, the clinical signs shown by cats have tended to be mild respiratory signs, and the animals have recovered uneventfully. Dogs appear to be less susceptible to infection and rarely show any clinical signs,” she continued.

Prof. Nicola Decaro from the department of Veterinary Medicine at the University of Bari Aldo Moro in Italy, who was not involved in the study, told MNT,

“Similar to other animals, cats and, to a lesser extent, dogs are susceptible to SARS-CoV-2 infection, especially if they live in a heavily contaminated environment, as are COVID-19-positive households.”

Previous work and Delta

“In a study conducted in northern Italy during the first wave of the pandemic, we detected SARS-CoV-2 antibodies in 3.3% and 5.8% of tested dogs and cats, respectively, with a higher seroprevalence in animals from COVID-19-positive households. In other studies, dogs and cats positive for SARS-CoV-2 RNA shed a virus that was genetically identical to that of their owner[s],” Prof. Decaro added.

“Therefore, contact between human patients [who have contracted SARS-CoV-2] and their pets is associated with viral transmission to dogs and cats. The observation of clinical signs in cats and especially in dogs is not frequent, with most reports accounting for the occurrence of a mild respiratory and sometimes [gastrointestinal] disease.”

“However, it is presumable that the same pathogenetic mechanisms responsible for the onset of myocarditis in COVID-19-positive humans are also involved in the occurrence of myocardial disease in pets, even if with a low frequency,” he continued.

The researchers conclude that pets can contract the B.1.1.7, or Alpha, variant of the virus. However, further research is necessary to determine how exactly it affects pets.

“We have noticed a rapid decline of myocarditis cases since April this year, and we are now back to the historical incidence of myocarditis — around 1–1.5% of all our cardiac cases,” said Dr. Ferasin. “We are not sure whether the relatively new Delta variant can infect dogs and cats and cause similar heart problems, so we will remain vigilant in this respect.”

The researchers note some limitations to their results. For instance, diagnoses of myocarditis could not be confirmed due to risks associated with an invasive procedure. They also point out that as they did not have a control group, it is not possible to say whether there is a direct link between COVID-19 and the condition.

Moreover, the study included a very small number of animals.

For pet owners

For people who have COVID-19 or who think they might have it, Dr. Ferasin recommends “washing hands thoroughly before and after touching their pets, and wearing a mask whenever they are in close proximity to their dog or cat. Similarly, if a pet presents clinical signs that could be potentially associated with COVID-19, our advice is to contact their primary vet for advice.”

“Owners [who may have contracted SARS-CoV-2] should avoid contact with their animals, just as they should avoid contact with other people,” said Dr. Hosie.

“If no one else can look after their pet, owners should wear a mask when preparing their pet’s food to avoid [passing on the virus to it]. Any cat from a COVID-19 household should not be taken into another household,” she continued.

“There is no evidence that virus can be transmitted from pets to humans, although it would be difficult to gather such evidence and to exclude the possibility of [transmission] from other sources,” Dr. Hosie noted.

“It is important that we continue to investigate SARS-CoV-2 [cases] in animals, as we do not know how frequently virus can be transmitted between animals or whether disease can be more severe in certain groups of animals. Currently, all efforts are focused on controlling infections in humans, but, in the longer term, other animal species might form a viral reservoir and could therefore perpetuate [transmission] in humans if they are not identified as potential sources of SARS-CoV-2,” she added.

“We need to develop systems to improve the sharing of information between public health and veterinary services to better investigate situations where a person who [has contracted] SARS-CoV-2 reports being in contact with pet or other animals,” Dr. Hosie concluded.

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