The novel coronavirus causing the COVID-19 pandemic can be transmitted between domestic cats even though infected cats may not show any symptoms, according to a research team working in the Japanese capital and Wisconsin.

Researchers from the University of Tokyo and University of Wisconsin-Madison published the findings online Wednesday in the New England Journal of Medicine.

Yoshihiro Kawaoka, a veterinarian and professor in the research team, recommends cat owners keep their pets indoors as they may contract the virus without the owner ever being aware.

The study said that while there is no evidence of the virus being transmitted from cats to humans, it is necessary to get a better understanding of the potential role of pets in the pandemic.

The U.S. Centers for Disease Control and Prevention and the U.S. Department of Agriculture's National Veterinary Services Laboratories confirmed in April that two pet cats were infected with the virus causing respiratory disease, and infections among cats have been reported in Belgium and Hong Kong as well.

The CDC said at that time there was no evidence that pets play a role in spreading the virus in the United States.

The research team took the virus from a human and infected three cats with it by putting large doses into the eyes, nostrils, mouth and trachea of the test subjects in a laboratory in the United States.

The infected cats were then each housed with an uninfected cat and within five days, the uninfected cats tested positive for the virus via nasal swabs.

Following the positive tests, all six cats continued testing positive for about five days, according to the team.

Blood tests showed that they produced antibodies for 24 days after the first positive test.

All six cats maintained normal body temperature, weight and behavior throughout the experiment and none showed any symptoms of the virus, according to the research team.

Pointing to evidence that humans can transmit the virus to cats and that cats can spread it to other cats, pet owners "should keep a distance from their cats" if they are found to have been infected, Kawaoka said.

The team also noted the importance of employing simple hygiene precautions, such as washing hands, and avoiding obviously ill animals, in protecting the health of both humans and animals.

Lions and tigers at the Bronx Zoo in New York exhibited symptoms of respiratory illness and tested positive for the coronavirus in April after a zookeeper was infected with the virus, according to U.S. media reports.

It is more likely that humans are giving the virus to their pets, rather than pets causing humans to become ill, according to the researchers.

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