Cats can fight off COVID-19 with no symptoms of infection

Scientists at Universitat Autònoma de Barcelona have investigated the case of the first known cat infected with SARS-CoV-2 in Spain. The researchers ultimately confirmed that cats produce antibodies that not only block the spread of the virus, but also protect cats from developing any symptoms.

The 4-year-old cat named Negrito lived with a family affected by COVID-19. When the cat seemed to be having respiratory difficulties, he was diagnosed with a terminal case of hypertrophic cardiomyopathy and euthanized at a veterinary hospital.

A necropsy performed at the High Biosafety Level Laboratories of the Animal Health Research Center (CReSA) confirmed that Negrito suffered from feline hypertrophic cardiomyopathy and had no other symptoms compatible with a coronavirus infection. Meanwhile, testing showed that the cat had been infected by SARS-CoV-2 with a low viral load.

The experts performed serological tests on Negrito and on another cat that also lived with the same family, Whisky, who had not displayed any symptoms of coronavirus. The tests revealed that both cats had developed antibodies against SARS-CoV-2. 

“In both cases we have detected neutralizing antibodies, in other words, they have the ability to bind to the virus and block it, this is important because it shows us that the immune system of cats can deal with SARS-CoV-2 and, in these specific cases, protect them from developing symptoms,” said study co-author Julià Blanco. 

Ongoing trials have shown that, in addition to becoming infected with SARS-CoV-2, cats can transmit the virus to nearby cats without any clinical signs. However, the researchers suspected that both Negrito and Whisky had been infected by their owners because they did not have contact with other cats.

The genetic sequence of the virus that infected Negrito turned out to share 99.9 percent similarity with the virus of one of the owners, who had died from COVID-19. Study co-author Marc Noguera-Julián said that this suggests that the cat became directly infected from family members.

Considering the number of humans infected with COVID-19 compared to the relatively few cases in animals, the experts say that animals are not playing a significant role in the spread of the virus.

“Pets play a negligible role in the epidemiology of SARS-CoV-2 and, in particular, cats become very residually infected and there is no evidence of transmission of the virus to humans. This is a case of reverse zoonosis, in which cats are the side victims without the virus causing them health problems,” said study co-author Júlia Vergara-Alert.

There has been one reported case in the Netherlands in which a farmer became infected with SARS-CoV-2 through a minks cat, which is the first known potential case of human transmission from a cat.

“We want to check if the case of Negrito and Whisky has been punctual or is repeated in more cases; in this way we will have more scientific information on how the most common pets can become infected with SARS-CoV-2 and to what degree,” said study co-author Professor Joaquim Segalés. 

“So far, it is known that around the world there have been some cases of cats and dogs that have become infected through their owners, but these animals have not suffered a serious illness and there is no evidence that they have transmitted the virus to their owners.”

The study is published in the journal Proceedings of the National Academy of Sciences.

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By Chrissy Sexton, Earth.com Staff Writer