About 120 black-footed ferrets, among the most endangered mammals in North America, were injected with an experimental Covid-19 vaccine aimed at protecting the small, weasel-like creatures rescued from the brink of extinction four decades ago.
Vaccinating such vulnerable species against the disease is important not only for the animals’ sake, experts say, but potentially for the protection of people. Some of the most pernicious human diseases have originated in animals, including the new coronavirus, which is believed to have spread from bats to an intermediary species before jumping to humans and sparking the pandemic.
“For highly contagious respiratory viruses, it’s really important to be mindful of the animal reservoir,” said Dr. Corey Casper, a vaccinologist and chief executive of the Infectious Disease Research Institute in Seattle. “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.”
“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,” Rocke said.
Rocke began working on the experimental vaccine in the spring, as she and Pete Gober, black-footed ferret recovery coordinator for the US Fish and Wildlife Service, watched reports about the new coronavirus with growing alarm. An exotic disease is “the biggest nemesis for ferret recovery,” said Gober, who has worked with black-footed ferrets for 30 years. “It can knock you right back down to zero.”
The ferrets are a native species that once roamed vast areas of the American West. Their ranks declined precipitously over many decades as populations of prairie dogs, the ferrets’ primary source of food and shelter, were decimated by farming, grazing and other human activity.
In 1979, black-footed ferrets were declared extinct — until a small population was discovered on a ranch in Wyoming. Most of those rare animals were then lost to disease, including sylvatic plague, the animal version of the Black Death that has plagued humans. The species survived only because biologists rescued 18 ferrets to form the basis of a captive breeding program, Gober said.
Would the same technique work against the virus that causes Covid-19? Under the research authority granted by the Fish and Wildlife Service, the scientists were free to try.
“We can do these sorts of things experimentally in animals that we can’t do in humans,” Rocke noted.
Rocke acquired purified protein of the SARS-CoV-2 virus from a commercial producer. She mixed the liquid protein with an adjuvant, a substance that enhances immune response, and injected it under the animals’ skin.
The first doses were given in late spring to 18 black-footed ferrets, all male, all about a year old, followed by a booster dose a few weeks later. Within weeks of getting the second shots, tests of the animals’ blood showed antibodies to the virus, a good — and expected — sign.
By early fall, 120 of the 180 ferrets housed at the center were inoculated, with the rest remaining unvaccinated in case something went wrong with the animals, which generally live four to six years in captivity. So far, the vaccine appears safe, but there’s no data yet to show whether it protects the animals from disease. “I can tell you, we have no idea if it will work,” said Rocke, who plans to conduct efficacy tests this winter.
But Rocke’s effort makes sense, said Casper, who has created several vaccines for humans. Rocke’s approach — introducing an inactivated virus in an animal to stimulate an immune response — is the basis for many common vaccines, such as those that prevent polio and influenza.
Gober said he is optimistic that the ferrets are protected, but it will take a well-designed study to settle the question. Until then, he’ll work to keep the fragile ferrets free of Covid-19. “The price of peace is eternal vigilance, they say. We can’t let our guard down.”
The tougher task is doing the same for people, Gober observed.
“We’re just holding our breath, hoping we can get all the humans vaccinated in the country. That will give us all a sigh of relief.”