Cheetahs at the Maryland Zoo are getting COVID vaccines. Here’s what researchers are hoping to learn.

In the next few weeks, two African cheetahs living at the Maryland Zoo in Baltimore will walk to the edge of their habitat, sit like house pets and allow a keeper to pull their tails through an opening in the fence.

This is how the cheetahs, Bud and Davis, will get their COVID-19 vaccines.


Two or three weeks later, they will repeat the process so their keeper can get a blood sample.

There will be another vaccination and blood will be taken six times in all during the year. The samples will become part of a nationwide study seeking to understand how well the particularly vulnerable species is protected against the deadly coronavirus.


The study involves at least 40 U.S. zoos and is organized by the Maryland Zoo’s chief veterinarian on behalf of the Association of Zoos and Aquariums.

The trial is only for big and small cats. At the Maryland Zoo, it only includes those with tails long enough to extend through the fence and trained (with food) to tolerate the blood draws.

But 32 animals at the zoo in Baltimore’s Druid Hill Park will receive donated vaccines. Also getting shots will be primates such as chimpanzees, otters and badgers, and other species of animals that somewhere and sometime during the pandemic caught COVID-19.

“It’s the big cats that seem so susceptible, and we don’t really know a lot about why,” said Dr. Ellen Bronson, the zoo’s senior director of animal health, conservation and research. “We know a lot of nondomestic cats have gotten sick with COVID-19.”

Bronson will send batches of blood from the animals to the Cornell University Animal Health Diagnostic Center in Ithaca, New York, where researchers hope the study shows the vaccines produce enough antibodies to fight off more serious or repeated infections from the coronavirus in the animals.

They also hope this and subsequent studies will give them clues about protecting other threatened or endangered species housed at the zoos, as well as other wild and domestic animals — and the humans who come in contact with them, she said.

The trial method is similar to how scientists assess vaccines for children, by measuring the antibodies rather than counting those infected after they are inoculated, though they will monitor that too. Antibodies are proteins produced by the body after exposure to the virus or a vaccine that fight off infection.

So far, the cheetahs and other animals have been kept safe by deploying many of the same precautions most humans are taking. Zoo visitors must wear masks when indoors and in some areas, additional barriers have been installed to keep people farther from animals.


There are no reports of infection in Maryland Zoo animals, or pets in the state for that matter. But various animals around the country and world have become sick and some have died from COVID-19, the disease caused by the virus, likely after being infected by humans.

The U.S. Department of Agriculture has reported 346 cases of COVID-19 in zoo animals and pets. Cats lead the pack at 110 cases, followed by infections in dogs, tigers, lions, gorillas, snow leopards, otters and a few others. A small number of U.S. farmed minks also have been infected.

For now, the U.S. Centers for Disease Control and Prevention said the risk that animals transmit COVID-19 back to people remains low.

But they do seem to give the virus to one another. Globally, there have been outbreaks on mink farms in Denmark, and earlier this month, hamsters from pet stores in Hong Kong tested positive, leading to mass culling of the animals.

Animal and coronavirus experts say more studies are needed to see how and which animals are most likely to get infected so they can be protected — and prevent them from harboring viruses that can mutate and be potentially transmitted back to people in a new or more dangerous form.

“The possibility is there,” said Matthew Frieman, a longtime coronavirus researcher and professor of microbiology and immunology in the University of Maryland School of Medicine.


He noted a major theory of the pandemic’s origin involves the virus passing from an animal, likely a bat, to another animal commonly sold to people in the food markets of Wuhan, China.

Previous coronaviruses also likely jumped from animals to people and caused other outbreaks, including one involving SARS first identified in China in 2002 and MERS first found in Saudi Arabia in 2012.

Still, Frieman said, with this coronavirus, “there is not a lot of evidence of additional animal-to-human spread.”

The wide-ranging species of animals found to have COVID-19, however, causes some concern because that’s different from past coronaviruses.

“We certainly want to protect vulnerable animals as much as possible,” he said. “And we need to know more about the kinds of animals infected, using zoos as sentinels for wild animals.”

Many of the animals in the Maryland Zoo and elsewhere are threatened or endangered, Bronson said, making their protection especially important. Around the country, zoos have reported infections in many animals, but cat species account for most: lions, tigers, snow leopards, cougars and lynx.


The scientists said infections in the wild are far tougher to count.

The concern is that wildlife doesn’t always stay in the wild, with deer, squirrels, foxes and rabbits, for example, often coming in contact with humans. If deer are infected with a variant from people and it mutates enough and poses a new threat, existing vaccines may not be protective.

That’s why the studies are so important, said Frieman, who informally consults with the Maryland Zoo and has been known to stop by over the years and collect bat droppings to check for coronaviruses.

If there is a wildlife outbreak, he said, many animals could be inoculated by leaving vaccine-infused bait in nearby woods.

Other researchers are monitoring wildlife infections. Those at the University of Minnesota announced Wednesday that they had tested 600 wild animals and found coronavirus only in white-tailed deer, and not in bats, coyotes, squirrels and mice.

Nine of 142 deer were positive.

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“As new SARS-CoV-2 variants emerge, it is important to monitor wildlife for the virus in areas where the animals may contract infections from human contact, and consequently, become reservoirs and sources of future infections,” said veterinarian Jeff Bender, the study’s lead author and also a professor at the University of Minnesota’s School of Public Health.

“We’ll especially need to determine which animals are susceptible, if they show signs of disease, and if they are capable of transmitting the virus to other animals or people,” he said in a statement.

The research follows similar studies in Canada, Iowa and Ohio, where the virus was found in about a third of deer samples, according to the Minnesota researchers.

Officials are now coordinating around the country on further deer studies to ensure new variants don’t behave differently and lead to reinfections in humans or spread to new species.

Back at the Maryland Zoo, the big cats are ready to assist in the research, even if they appear unaware of their role in advancing science and perpetuating their species and others.

On a recent day, a lion pair lounged together and ignored the only visitors of the day. Bud and Davis, the cheetahs, took turns surveying their territory from atop a giant rock.


As Bronson looked in on her study volunteers, she said: “I’m hopeful we’ll have a tool to use, like in people, to protect this sensitive species.”