BROOKFIELD, IL — The reported infection of animals with COVID-19 has been documented around the world. Most have been infected after contact with their human owners or caretakers.

Veterinarians say part of the fight against the coronavirus includes vaccinating zoo animals to prevent what’s known as spillover infections.

Scientists say most emerging infectious diseases originate in animals.

In fact, the zoonotic origin of the 2003 SARS outbreak in Asia was traced back to cave-dwelling horseshoe bats in China. It eventually reached animals in live markets where it spilled over into humans.

“There's a huge interconnectedness between animals and people when it comes to a different number of different viruses and other illnesses,” said Dr. Mike Adkesson, vice president of clinical medicine at the Chicago Zoological Society

Still, the source of SARS-CoV-2 or COVID-19 is still an official mystery.

An unclassified report from the office of the Director of National Intelligence last month was only confident that it was “not developed as a biological weapon.”

What we do know is that the novel coronavirus is not a human-only infection.

“We have seen cases of COVID-19 occur in a number of different species around the country in different zoos, primarily primates, large cats such as tigers, lions, leopards, as well as a number of smaller carnivores like otters and mink,” said Adkesson.

Late last week, more than a dozen western lowland gorillas reportedly tested positive for COVID-19 at Zoo Atlanta. Their care team noticed changes in appetitive and respiratory issues.

“Coughing, sneezing, lethargy, the animals just clearly feel a little bit under the weather, the same way that we see those same signs and symptoms in people,” said Adkesson.

While animals are not playing a major part in the transmission of the virus, they are clearly susceptible.

“Part of the concern is that those animals are able to spread it to other animals and potentially able to spread it back to people,” said Adkesson.

The CDC says there have been isolated cases of domestic dogs and cats that have become infected and have been able to transmit COVID-19 back to people.

Zoos across the country are now vaccinating their animals beginning with carnivores, primates, and big cats. The emergency use authorization of the vaccine Zoetis requires two doses three weeks apart.

“We're still pretty early on in this process, but we know that the vaccine is safe from the trials that Zoetis has done with it,” said Adkesson. “So, it's really just a question of how efficacious it's going to be in the long run for our animals.”

Caretakers at the Brookfield Zoo outside Chicago have been required to mask and maintain social distancing as much as possible from the animals.

“There have been cases that have emerged in other zoos, though, even with those guidelines in place. So, we know that the virus is able to infect many of these animals the same way it's able to infect people,” said Adkesson.

It’s another reminder that the health of humans, animals, and the environment is intertwined.

Initial tests show that lowland gorillas at Zoo Atlanta have the COVID-19 virus, the zoo said in a media update on its website.

Officials said Friday they are waiting to confirm the diagnosis after sending test samples to the National Veterinary Services Laboratory in Ames, Iowa.

The animals were tested after employees saw some of them coughing, having nasal discharge, and showing changes in appetite. Analyses by the Athens Veterinary Diagnostic Laboratory at the University of Georgia resulted in presumptively positive results for the SARS-CoV-2 virus, which causes COVID-19.

Video above: Zoos seeking COVID-19 vaccinations for animals

The affected gorillas are being treated with monoclonal antibodies and samples from the zoo's entire gorilla population have been taken for testing, said the release. The zoo plans to continue to test the animals regularly.

"The teams are very closely monitoring the affected gorillas and are hopeful they will make a complete recovery," said Sam Rivera, the Senior Director of Animal Health. "They are receiving the best possible care, and we are prepared to provide additional supportive care should it become necessary."

Zoo officials said they do not know exactly how the gorillas became infected. They said the virus might have been passed to the animals by a fully vaccinated, asymptomatic, COVID-positive employee who was wearing Personal Protective Equipment (PPE), which is standard practice when working with great apes, said the release.

"While humans are known to be able to transmit the virus to animals such as gorillas, and these cases have occurred at other zoos, there is currently no data to suggest that zoo animals can transmit the virus to humans," according to the release. "Regardless, Zoo Atlanta visitors do not pose a transmission threat to the gorillas or vice versa given the distance between the areas used by guests and the animals' habitats."

The U.S. Department of Agriculture (USDA) and Georgia's State Veterinarian have approved Zoo Atlanta to use a vaccine developed specifically for animals, and the gorillas will receive the vaccine once they recover. For now, the zoo plans to vaccinate its "Bornean and Sumatran orangutans, Sumatran tigers, African lions, and clouded leopard" populations, the release said.