Confusion about whether millions of cats should be placed on lockdown has created alarm among pet owners and raised the prospect of Larry the Downing Street cat having to go into isolation.

Cat owners crashed the website of the British Veterinary Association on Wednesday after it appeared to suggest the UK’s estimated 10.9 million cats should be on curfew during the coronavirus outbreak.

The association was forced to clarify that only cat owners who are self-isolating with symptoms of coronavirus should keep their pets indoors, after a study found cats can spread the virus.

No 10 has been openly flouting the revised advice while the prime minister has been suffering from coronavirus. Larry has been free to wander up and down Downing Street. He was photographed waiting to be let in on Tuesday as Boris Johnson was being treated in intensive care.

And last week while the prime minister was self-isolating in his flat in No 11, Larry was photographed having his tummy tickled by a Downing Street policeman.

Larry waits heads to be let into No 10 as Boris Johnson was being treated in intensive care for coronavirus. Photograph: Tolga Akmen/AFP via Getty Images

He may now have to undergo a spell of isolation to comply with the new guidance.

The veterinary association’s president, Daniella Dos Santos, made clear that cats from infected or self-isolating households should be kept indoors.

“We are not advising that all cats are kept indoors. Only cats from infected households or where their owners are self-isolating, and only if the cat is happy to be kept indoors.”

Some cats cannot stay indoors due to stress-related medical reasons.

She acknowledged that the association should have been clearer earlier this week when responding to questions from the BBC about advice for pet owners.

It appears that dogs do not show symptoms, but cats can show clinical signs of the disease Daniella Dos Santos, British Veterinary Association

She said: “It’s incredibly important that information and advice for the public is clear and we regret that this story will have caused worry and upset amongst cat owners.”

The BVA’s advice comes after a study in China revealed Covid-19 can be transmitted between cats, but not dogs.

A team at the Harbin Veterinary Research Institute in China found cats are highly susceptible to Covid-19 and appear to be able to transmit the virus through respiratory droplets to other cats. But there was no direct evidence that felines could also infect people.

“Surveillance for Sars-CoV-2 [coronavirus] in cats should be considered as an adjunct to elimination of Covid-19 in humans,” the paper concluded.

It followed reports of a pet cat in Belgium being infected with Covid-19. The cat developed breathing difficulties, diarrhoea and vomiting a week after its owner started showing symptoms. Subsequent tests by vets at the University of Liège showed the animal was infected with coronavirus.

Dos Santos said: “There have been a tiny number of cases of Covid-19 in animals, and in all cases it is likely that the transmission was human to animal. There is no evidence that pets can pass Covid-19 to their owners.

“From the small number of cases, it appears that dogs do not show symptoms, but cats can show clinical signs of the disease.”

Nadia, a four-year-old female Malayan tiger at the Bronx zoo in New York, has tested positive for coronavirus. Photograph: WCS/Reuters

A four-year-old tiger called Nadia at Bronx zoo in New York tested positive for Covid-19 earlier this week. Nadia and six other tigers and lions that have also fallen ill are believed to have been infected by a zoo employee who was not yet showing symptoms, the zoo said.

A Downing Street spokesman said Larry was “absolutely fine and going about his business in the usual way”. The government has said there is no evidence that pets can pass on coronavirus to owners.