Hong Kong will cull more than 2,000 hamsters and ban the import of small animals after a pet shop worker, a customer and at least 11 hamsters tested positive for the delta variant of the coronavirus.

Officials said Tuesday that it was not clear that the virus had been transmitted to humans from imported hamsters. But they called on residents to surrender hamsters imported since Dec. 22 to be tested and euthanized to prevent any further spread.

“They’re excreting the virus, and the virus can infect other animals, other hamsters and also human beings,” said Thomas Sit, assistant director of Hong Kong’s Agriculture, Fisheries and Conservation Department. “We don’t want to cull all the animals, but we have to protect public health and animal health. We have no choice — we have to make a firm decision.”

The cluster was traced to a worker at the Little Boss pet shop in the Causeway Bay district of Hong Kong island who was confirmed Monday to have contracted the delta variant. Further tests uncovered another infection in a customer who had a brief transaction with the worker while exchanging a cage and buying hamster food with her daughter Jan. 7. A preliminary test indicated that the customer’s husband had also contracted the coronavirus.

Further testing found 11 infected hamsters in the shop and positive samples from cages at the company’s warehouse. Health officials said they had found no precedent for pet hamsters passing the coronavirus to humans but noted that hamsters had been infected in laboratories.

Officials said that two shipments of hamsters from the Netherlands were particularly worrying, including about 1,800 brought in Dec. 22 and more than 800 that arrived Jan. 7.

All hamsters at the city’s 34 licensed shops will be seized for testing and then culled, officials said. Anyone who bought a hamster after Dec. 22 is asked to surrender the animal to be tested and euthanized.

Pet shops that sell hamsters will also be closed for cleaning, and authorities will test the shops’ rabbits, chinchillas and guinea pigs. Shops may reopen once those animals are shown not to be infected.

Dr. Maria Van Kerkhove, the World Health Organization’s technical lead for coronavirus response, said Tuesday that the risk that animals like the hamsters in Hong Kong would infect humans “remains low, but it is something we are constantly looking at.”

Hong Kong, which has a painful history of infectious disease, including nearly 300 deaths from severe acute respiratory syndrome in 2003, has taken aggressive measures to cut the risk of animal transmissions in the past. In 1997, it slaughtered more than 1 million chickens — every chicken in the territory — to stop the spread of an avian flu virus, and the city has since carried out smaller culls when infected birds are found.

This article originally appeared in The New York Times.