Twenty-seven conservation experts from the Great Ape Health Consortium urged a letter to Nature Tuesday that all great ape tourism be suspended and field research be reduced in an effort to protect already vulnerable species from contracting COVID-19.

"The Covid-19 pandemic is a critical situation for humans, our health and our economies," lead letter writer Thomas Gillespie of Emory University told The Guardian. "It's also a potentially dire situation for great apes. There is a lot at stake for those in danger of extinction."

Since no gorilla, orangutan or chimpanzee has yet caught COVID-19, it is impossible to know exactly how it would impact our closest genetic relatives, but human respiratory illnesses as mild as the common cold have proved fatal to gorillas, The Associated Press reported.

Some parks are already taking measures to protect the animals. Virunga National Park in the Congo, which is home to a third of the world's mountain gorillas, is closing to human visitors until June 1 to prevent transmission, and Rwanda is also closing three parks home to gorillas and chimpanzees to tourists and researchers.

In Malaysian Borneo, meanwhile, the Sepilok Rehabilitation Centre is also closing to protect orangutans.

"This disease could be fatal for the already critically endangered orangutan: it is a risk that we cannot afford to take," Susan Sheward of Orangutan Appeal UK explained to The Guardian.

The International Union for the Conservation of Nature issued guidelines in response to the coronavirus March 15 urging interactions between humans and apes to be reduced to the minimum possible. It advised that the normal seven meter (approximately 23 foot) distance between apes and humans be expanded to 10 meters (approximately 33 feet) and that no one who is ill or has been in contact with someone who was ill within the past 14 days be allowed to interact with apes.

However, Kenyan conservationist Paula Kahumbu explained how, in the case of COVID-19, that might not be effective.

"We know that gorillas are very sensitive to human diseases," she told The Associated Press. "If anyone has a cold or a flu they are not allowed to go and see the gorillas. With coronavirus having such a long time of no symptoms in some cases, it means that we could actually put those gorillas at risk."

The one risk with shutting parks to visitors is that it might encourage the presence of poachers. The Great Ape Health Consortium said that risk assessments would have to be conducted to continue the parks' conservation work while protecting apes from the new illness.

"Such efforts should include ways to offset loss of earnings from tourism, while taking care not to interfere with work to save human lives," they wrote.