Experimental Covid-19 Vaccine Reaches America’s Endangered Ferrets

Black-footed ferrets are close relatives of minks, which have seen coronavirus outbreaks on fur farms

A black-footed ferret kit with its tongue sticking out sits on hay in an enclosure
Scientists at the National Black-footed Conservation Center in Colorado inoculated 120 black-footed ferrets against the coronavirus that causes Covid-19. Image by Ryan Moehring / USFWS via Wikimedia Commons under CC BY 2.0

This fall, scientists at the National Black-footed Ferret Conservation Center in Colorado administered experimental vaccines to 120 endangered black-footed ferrets in the hopes of protecting them from the virus that causes Covid-19 in humans, JoNel Aleccia reports for Kaiser Health News.

The ferrets were declared extinct in 1979, but a small group was discovered on a ranch in Wyoming two years later. Biologists whisked away 18 of the critters to form a captive breeding program. Diseases like sylvatic plague wiped out the ferrets that the biologists left behind. Now, the black-footed ferret population is made of hundreds of individuals, but novel diseases remain a constant threat.

U.S. Fish and Wildlife Service black-footed ferret recovery coordinator Pete Gober tells Kaiser Health News that exotic disease is “the biggest nemesis for ferret recovery. It can knock you right back down to zero.”

Black-footed ferrets are the only ferret species native to North America. The ferrets are identifiable by their elongated stature, racoon-like bandit masks and dark-colored legs and tail. Prairie dogs make up about 90 percent of a black-footed ferret’s diet, but the small carnivores also eat mice, rats, ground squirrels and other small animals. They’re nocturnal and usually live alone in prairie dog burrows.

Through captive breeding programs and reintroduction to the wild, there are now hundreds of black-footed ferrets living in North America. Smithsonian’s Conservation Biology Institute has participated in the breeding program since 1988, and has seen more than 960 ferrets born at SCBI, 200 of which were released into the wild. In May 2020, a ferret at the National Zoo named Potpie gave birth to six black-footed ferret kits.

EcoHealth Alliance’s executive vice president for health and policy William Karesh cites black-footed ferrets similarity to other ferrets, which have been susceptible to coronavirus infections in lab experiments, as cause for concern, reports Science magazine’s David Grimm. Ferrets are also close relatives of minks, which have seen massive outbreaks of coronavirus infections in European and U.S. fur farms. The outbreaks have led to the culling of millions of mink in Europe, and in December, the U.S. identified the first case of a coronavirus infection in a wild animal, a wild mink found near a mink fur farm in Utah.

“We don’t have direct evidence that black-footed ferrets are susceptible to Covid-19, but given their close relationship to minks, we wouldn’t want to find out,” says National Wildlife Health Center biologist Tonie Rocke, who is working on the ferret vaccine, to Kaiser Health News.

The ferrets’ experimental vaccine is a mixture of the coronavirus’ spike protein, which studs its surface, and an adjuvant, which increases the immune system’s response so that it will learn how to recognize the spike protein and destroy the coronavirus if it ever infects the inoculated animal. The scientists vaccinated about two-thirds of the ferrets at the Conservation Center, leaving 60 unvaccinated in case something goes wrong, per Kaiser Health News.

Black-footed ferrets are not the only endangered animal at risk of catching Covid-19 from an infected human. A study published in September in the Proceedings of the National Academy of Sciences analyzes how susceptible 410 vertebrates might be to the virus based on how similar their ACE2 protein is to humans’ ACE2, Brian Resnick reports for Vox. The virus that causes Covid-19 uses humans’ ACE2 to hack into cells and start an infection, so the more similar another species’ protein is to ours, the more likely it is that the virus can infect that animal, too.

The study found that black-footed ferrets fall in the lowest-risk category because about a third of their ACE2 is different than the human version of the protein. But primates like gorillas, orangutans and chimpanzees have an identical version of the protein to ours, putting them at very high risk of an infection.

“You can’t provide the same level of intensive treatment to a wild gorilla as you would a human being, who you can put in a hospital ward, put on a ventilator for days and days,” says Gladys Kalema-Zikusoka, a veterinarian and conservation scientist at Uganda’s Bwindi Impenetrable National Park, to Vox.

Protecting endangered animals from a coronavirus infection helps keep them safe from extinction, but protecting other animals from the virus is also a way to protect ourselves. Scientists worry that if the virus starts to pass between wild animals, it could establish a reservoir and jump back into humans at a later, nearly unpredictable time.

“For highly contagious respiratory viruses, it’s really important to be mindful of the animal reservoir,” says Infectious Disease Research Institute vaccinologist Corey Casper to Kaiser Health News. “If the virus returns to the animal host and mutates, or changes, in such a way that it could be reintroduced to humans, then the humans would no longer have that immunity. That makes me very concerned.”