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December 01, 2021

Zoos vaccinate animals against SARS-CoV-2

Big cats, other mammals at zoos around the world have contracted the virus
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Big cats, nonhuman primates, otters, and hyenas at zoos around the world have contracted the SARS-CoV-2 virus. Although most have recovered, zoos have been vaccinating some of their animals with an experimental vaccine from Zoetis.

Vaccination at the San Diego Zoo and infections in big cats at zoos globally were the subjects of two sessions on Oct. 4 during the 2021 virtual conference of the American Association of Zoo Veterinarians and European Association of Zoo and Wildlife Veterinarians, which ran weekly from early October through early November.

Vaccinating zoo animals

Back in July, Zoetis announced that it was donating more than 11,000 doses of an experimental vaccine against SARS-CoV-2 to help protect over 100 mammalian species living at nearly 70 zoos and more than a dozen conservatories, sanctuaries, academic institutions, and government organizations located in 27 states.

The initial development work and studies for the vaccine were completed on dogs and cats. In these preliminary studies, the vaccine was demonstrated to be safe and to have a reasonable expectation of efficacy, according to Zoetis.

Connor is one of three tigers at the San Diego Zoo that were vaccinated against SARS-CoV-2 and later tested positive for the virus. The tigers were not showing any concerning signs of illness other than intermittent cough, fatigue, and occasionally decreased appetite. (Courtesy of the San Diego Zoo)

Development work on the same vaccine then shifted to mink as the incidence of SARS-CoV-2 infection in that species increased. The U.S. Department of Agriculture and state veterinarians authorized the vaccine for experimental use on a case-by-case basis. The vaccine has been used on some mink farms to generate data on safety and efficacy necessary for conditional approval by the USDA.

The July donation of vaccine to zoos followed Zoetis’ donation of vaccine in January in response to a request from the San Diego Zoo after gorillas at the Safari Park tested positive for the SARS-CoV-2 virus. During the zoo veterinarians’ conference, Dr. Ben Nevitt of the San Diego Zoo spoke about how the zoo has vaccinated animals.

With the early supply of vaccine, Dr. Nevitt said, the zoo vaccinated four orangutans, eight bonobos, and five gorillas. Minimal adverse effects were observed, with one orangutan holding her head and then the vaccine site and her daughter holding the vaccine site.

For the later supply of vaccine, the zoo performed a risk assessment of the mammal population, focusing on species at a higher risk because of their cellular virus receptors and their proximity to the public and the staff. The main zoo received 36 bottles of vaccine, and the Safari Park received 18. The bottles were 10-dose vials with a 24-hour shelf life after being punctured. Zoo staff members were able to get 11 doses if they were careful.

The animals were combined in groups of 10 or 11. The highest vaccine total was 54 animals in one day. Zoo personnel had to repeat everything 21 days later for the second dose. In total, the zoo vaccinated 171 animals—great apes, Old World primates, lemurs, felids, some canids, and certain other mammals. Minimal adverse effects were observed overall. Preliminary titer data suggested a higher antibody response in felids and canids than in primates, and the zoo might consider boosters for the great apes.

On Oct. 27, the San Diego Zoo released a statement saying that three tigers vaccinated against SARS-CoV-2 had tested positive for the virus. The tigers were not showing any concerning signs of illness other than intermittent cough, fatigue, and occasionally decreased appetite.

Infections in big cats

The first case of SARS-CoV-2 virus detected in any animal in North America was in a tiger in March 2020 at the Bronx Zoo in New York City. Four other tigers and three lions at the zoo also tested positive for the virus.

During the conference, Dr. Susan L. Bartlett of the Bronx Zoo presented “Global Retrospective Review of SARS-CoV-2 Infections in Non-Domestic Felids.” She said transmission events have continued to occur from humans to exotic cats.

From March 2020 to February 2021, there were confirmed cases in the Bronx, South Africa, Tennessee, Spain, Kentucky, Minnesota, Sweden, Indiana, and the Czech Republic, comprising 16 tigers, 14 lions, two cougars, three snow leopards, and one Amur leopard. Minnesota had an additional 12 tigers, four lions, and eight cougars with clinical signs suspected to be caused by SARS-CoV-2.

The first case of SARS-CoV-2 virus detected in any animal in North America was in Nadia the tiger in March 2020 at the Bronx Zoo in New York City. (Photo by Dr. Susan L. Bartlett)

About half of the animals received treatment, such as nonsteroidal anti-inflammatory drugs or antimicrobials, and most of the animals made a full recovery. Clinical signs lasted from one to 18 days, with a mean of eight days. The clinical signs were generally respiratory and less commonly gastrointestinal, with some lethargy and inappetance. An older tiger in Sweden, age 17, had to be euthanized.

Shortly after Dr. Bartlett’s presentation, the Great Plains Zoo in Sioux Falls, South Dakota, announced that a 2-year-old snow leopard infected with the SARS-CoV-2 virus died on Oct. 7 after experiencing a rapid decline of respiratory function. At press time, a necropsy was being performed to investigate the cause of death.

For the cases from March 2020 to February 2021, Dr. Bartlett said.SARS-CoV-2 infection was confirmed by a variety of diagnostic tests. Viral shedding in feces lasted longer than clinical signs. The source of infection for most cases was confirmed or presumed to be the zookeepers. For other cases, the source of infection was unknown, and there also was possible viral transmission between felids.

Before infection, prevention measures by zoo personnel generally consisted of cloth masks; gloves, especially for food preparation; and some social distancing. Afterward, protective measures consisted of Tyvek coveralls, mostly N95 or FFP3 masks, gloves, often face shields or goggles, shoe covers or dedicated boots, foot baths, and limited personnel.