When researchers accelerated the first human clinical trials of COVID-19 vaccines in late summer, a group of scientists in Colorado worked to vaccinate a far more fragile species.
About 120 black-footed ferrets, which are among the most endangered mammals in North America, were injected with an experimental COVID vaccine to protect the small, weasel-like creatures that were saved from extinction four decades ago.
The effort came months before U.S. Department of Agriculture officials accepted applications from veterinary drug manufacturers for a commercial vaccine against mink, a close cousin of ferrets. Cultivated minks, raised for their valuable fur, have died in the tens of thousands in the US and millions have been killed in Europe after getting the COVID virus from infected people.
Vaccinating such endangered species against the disease is not only important for the animals, say experts, but possibly also for the protection of humans. Some of the most harmful diseases in humans can be traced back to animals, including the new coronavirus, which is believed to have spread from bats to an intermediate species before jumping to humans and starting the pandemic.
The concern with animals like mink kept in overcrowded pens is that the human-borne virus can mutate as it spreads quickly in the susceptible animals and poses a new threat when it flows back onto humans. In November, Danish health officials reported that more than 200 cases of COVID with variants related to mink had been detected in humans, including a dozen with a mutation that scientists feared could undermine the effectiveness of vaccines. However, officials now say the variant appears to be extinct.
In the United States, scientists have not found similar COVID mutations in domestic mink populations, despite recently being concerned about the discovery of the first case of the virus in a wild mink in Utah.
“With highly contagious respiratory viruses, it’s really important to be careful of the animal reservoir,” said Dr. Corey Casper, vaccine doctor and executive director of the Infectious Disease Research Institute in Seattle. “When the virus returns to the animal host and mutates or changes in such a way that it can be reintroduced into humans, humans no longer have that immunity. I am very concerned about that. “
The newly vaccinated ferrets are the main risk to the animals themselves. They are part of a captive population at the National Black-footed Ferret Conservation Center outside of Fort Collins, Colorado, where no cases of COVID-19 have occurred to date. However, it is feared that the slender, furry creatures – known for their signature black eye mask, legs, and feet – are very susceptible to the effects of the disease, said Tonie Rocke, a scientist at the National Wildlife Health Center who tests the ferret vaccine. They are all genetically similar and come from a tight breeding pool that weakens their immune systems. And they likely share many of the traits that made the disease so deadly to minks.
“We don’t have direct evidence that black-footed ferrets are susceptible to COVID-19, but given their close relationship with mink, we don’t want to find out,” Rocke said.
Rocke began work on the experimental vaccine in the spring when she and Pete Gober, Black-footed Ferret Restoration Coordinator for the U.S. Fish and Wildlife Service, watched reports of the new coronavirus with growing concern. An exotic disease is “the biggest nemesis for ferret recovery,” said Gober, who has worked with black-footed ferrets for 30 years. “It can bring you right back to zero.”
Pete Gober, coordinator for the U.S. Fish and Wildlife Service’s Black Footed Ferret Restoration Program, pictured in 2016. (Ryan Moehring / USFWS via Flickr)
The ferrets are a native species that once roamed large areas of the American west. Their ranks declined sharply over many decades as populations of prairie dogs, the ferrets’ primary source of food and shelter, were decimated by agriculture, grazing, and other human activities.
In 1979, black-footed ferrets were declared extinct – until a small population was discovered on a ranch in Wyoming. Most of these rare animals were then lost to disease, including the sylvatic plague, the animal version of the black death that plagued humans. The species only survived because biologists rescued 18 ferrets to lay the foundation for a captive breeding program, Gober said.
In view of the impending new disease, Gober doubled the strict precautionary measures for infection prevention in the center, where more than half of the 300 black-footed ferrets live in captivity. Another 400 were reintroduced into the wild. Then he called Rocke, who had previously developed a vaccine to protect ferrets from Sylvat’s plague. A purified protein is used Yersinia pestis, the bacteria that causes the disease.
Would the same technique work against the virus that causes COVID-19? Under the research authority assigned by the Fish and Wildlife Service, the scientists could try it.
“We can do things like this experimentally in animals that we can’t do in humans,” noted Rocke.
Rocke acquired purified protein of a key component of the SARS-CoV-2 virus, spike protein, from a commercial manufacturer. She mixed the liquid protein with an adjuvant, a substance that boosts the immune response, and injected it under the animals’ skin.
The first doses were given to 18 black-footed ferrets in late spring, all male, all about a year old, followed by a booster dose a few weeks later. Within weeks of the second shot, tests on the animal’s blood showed antibodies to the virus, a good – and expected – sign.
By early autumn, 120 of the 180 ferrets housed in the center had been vaccinated, the rest remained unvaccinated in case something went wrong with the animals, which usually live in captivity for four to six years. So far, the vaccine seems safe, but there is no data 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 do efficacy tests this winter.
But Rocke’s efforts make sense, said Casper, who has developed several vaccines for humans. Rock’s approach – introducing an inactivated virus into an animal to stimulate an immune response – is the basis for many popular vaccines, including those used to prevent polio and influenza.
Inactivated virus vaccines to prevent COVID-19 have been tested on specific animals – and vaccines for humans, including CoronaVac, developed by Chinese company Sinovac Life Sciences. But efforts in Colorado could be among the earliest aimed at preventing COVID-19 in a given animal population, Rocke said.
Gober said he was optimistic the ferrets are protected, but it will take a well-designed study to clear the question. Until then, he will work to keep the fragile ferrets free from COVID-19. “The price of peace is eternal vigilance, they say. We cannot disappoint our guard. “
The harder job is to do the same for the people, Gober noted.
“We just hold our breath and hope that we can vaccinate everyone in the country. That will make us all breathe easy. “