BANGKOK — The tiny orangutan, no bigger than a house cat, was about 10 months old when he was rescued. Most of his nose had been sliced off, probably in the machete attack that killed his mother.

He was taken to a rehabilitation center near the city of Medan, on the Indonesian island of Sumatra, and raised with other orphans. Given the name Bina Wana, he was put through the center’s “forest school,” in which he learned how to climb trees, find food and survive in the wild.

Now about 6, Bina Wana had been scheduled to be freed soon as part of an ambitious program that has released more than 300 rescued Sumatran orangutans into the rainforest.

But as with so many of his human cousins, Bina Wana’s freedom has been put on hold by the coronavirus.

Scientists fear that the virus, which is thought to have originated in bats and jumped to humans, could just as easily jump to great apes — gorillas, chimpanzees, bonobos and orangutans — which share 97 per cent to 99 per cent of their DNA with people. All are highly endangered.

If the virus were to infect even one wild ape, experts fear it could spread unchecked and wipe out an entire population. There would be no way to stop it in the wild.

“We are worried about this and taking it very seriously,” said Ian Singleton, director of the Sumatran Orangutan Conservation Program, which has been raising Bina Wana since his 2014 rescue. “If it happens, it will be a catastrophe.”

Dogs, cats, minks and captive lions and tigers have all been infected with the virus and in many cases are believed to have caught it from people. An April study concluded that apes and African and Asian monkeys were “likely to be highly susceptible” to it. Experts also worry that the virus could sicken wild tigers, especially in India, where most of them live.

Orangutans, which can live more than 50 years, are Asia’s only great ape aside from humans and are found only on the islands of Sumatra and Borneo. Nearly 85 per cent of them inhabit Indonesia’s dwindling rainforests. The rest live in the northern part of Borneo that belongs to Malaysia.

“It may affect them less than humans, but it also may be even more deadly, and this is simply a risk we cannot take,” said the head of the Borneo Orangutan Survival Foundation, Jamartin Sihite, in announcing that its two rehabilitation centers in Indonesia would be closed to the public.

Indonesia has 33 facilities that keep orangutans, including animal parks, rehabilitation centers and zoos. The Environment and Forestry Ministry alerted them in early February that the virus posed a threat to the animals.

In mid-March, officials canceled all planned releases into the wild, closed the facilities to outsiders and ordered staff working with orangutans to wear protective gear. That was nearly two weeks before President Joko Widodo imposed social distancing measures across the country.

“We are being really careful so that there won’t be any transmission from humans to wild animals,” said the director of biodiversity conservation for Indonesia’s Ministry of Environment and Forestry, Indra Exploitasia. “Disease is one of the threats that can cause the extinction of a species.”

One rehabilitation center on Indonesian Borneo, the Center for Orangutan Protection, decided that the best way to protect its 16 orangutans was to return them to cages.

“We chose to lock down the orangutans to prevent the transmission of the virus,” said Ramadhani, the center’s rehabilitation manager, who like many Indonesians goes by one name.

Fewer than 72,000 orangutans live in the wild, according to government estimates. And they face other threats besides the coronavirus.

The Sumatran orangutan, of which there are about 13,700, once roamed widely over the vast island, but deforestation, particularly for palm oil plantations, has restricted its range to parts of northern Sumatra.

Of the three orangutan species, the most endangered is the recently identified Tapanuli orangutan, which numbers about 760 and lives in North Sumatra province. Its habitat is threatened by logging, a large gold mine and construction of the new Batang Toru hydropower dam.

The Borneo orangutan, which is also threatened by the conversion of forests to farmland, especially when land is cleared by fire, numbers about 45,600 in Indonesia after two decades of dramatic decline. About 11,700 live on the Malaysian side of the border.

The orangutans’ shrinking habitats have made them more vulnerable to encounters with local villagers, who sometimes kill the mothers to take their babies and sell them as pets.

Last year, a Sumatran orangutan was shot 74 times with a pellet gun and blinded by a teenage boy who tried to steal her baby. The mother was taken to the Sumatran Orangutan Conservation Program, where Bina Wana is, where she underwent surgery and survived. Her baby died en route.

The center receives dozens of orangutans each year. Many were rescued at a young age, like Bina Wana. Others suffered for years in captivity before being turned in by their owners or seized by authorities and brought to the center.

Some are too badly hurt to survive on their own. But most have a chance to return to the wild.

The program’s goal is to create two new self-sustaining populations in habitats where the species has not lived for perhaps a century.

The orangutans at the center have not seen much change since the pandemic began, Mr Singleton said, except that fewer people are working and they wear more protective clothing. Under the new protocol, a new team of caretakers rotates in every three weeks.

The center is building a new isolation unit with cages for up to five orangutans in case any newcomers are found to have the virus, Mr Singleton said.

“We are trying to prepare for every scenario,” he said. THE NEW YORK TIMES