“Tiger at US Zoo Tests Positive for Coronavirus, Becomes First Animal to Contract COVID-19,” proclaimed an April 2020 headline.
The story referenced 4-year-old Malayan tiger Nadia, who contracted COVID early in the pandemic, along with six other tigers at the Bronx Zoo, likely after being cared for by a presymptomatic zoo worker.
It was the first of what would become a steady stream of stories about animals who, like most of us, have contracted COVID. Among the menagerie they have, according to the US Centers for Disease Control and Prevention:
- Pets such as cats, dogs, ferrets and hamsters.
- Zoo animals such as lions, tigers, snow leopards, otters, hyenas, hippos and manatees.
- Mink that lives on farms.
- Fauna, including dozens of white-tailed and mule deer, a black-tailed marmoset, and a giant anteater.
COVID is no exception to “zoonotic” diseases that animals have transferred to humans, or vice versa. It is thought to have been transmitted from a bat, pangolin, or raccoon dog to humans, perhaps through an intermediary such as a pet (although a controversial “lab leak” hypothesis has not been fully debunked).
Similar to COVID, the 2009 H1N1 “swine flu” pandemic is believed to have been caused by North American and European pigs intermingling, mixing strains of the flu. West Nile Virus, which originated in arthropods and is transmitted by mosquitoes, was established in New York City in 1999 and has since become endemic in the US in monkeys, although it is believed to have originated in rodents.
Animals most likely triggered the COVID-19 pandemic, as many others have, but their role in it did not disappear afterwards. The pathogen now circulates in both populations, interbreeding and spilling over, even if such occurrences are relatively infrequent. And just like humans, animals continue to shape the pandemic, as new variants and subvariants mutate into hosts with fur, fur, and feathers before attempting to launch into the general population.
Scientists are watching the animal kingdom for signs of what’s to come next.
A host is a host
Scientists have recently begun tracking the spread of COVID in animals on publicly available data panels. One, launched late last month by the Wildlife Conservation Society and Australian researchers at the Vienna University of Veterinary Medicine, has so far documented 704 COVID-19 diagnoses in animals worldwide, in 39 countries and 27 species.
Among the revelations:
- There have been 117 documented infections in cats and 110 in dogs in the US.
- Mink are among the animals most commonly identified with COVID. In Greece alone, 159 American mink have been diagnosed, in addition to almost 150 in Spain and 250 in Lithuania.
- Most of the animals have been asymptomatic or have experienced respiratory symptoms. Minks are the most likely to die.
- Omicron subvariants are the most common strains identified in animals, although cases of Delta have also been documented.
The risk of contracting COVID from animals is small, says Dr. Mary Montgomery, a clinical educator in the Division of Infectious Diseases at Brigham and Women’s Hospital, a Harvard-affiliated center in Boston.
But it is real. COVID entered humans from animals, perhaps in multiple patients from multiple animal encounters in late 2019, according to a recent study, and may re-enter animals via humans in a process scientists call ” zoonotic transmission.
Just as COVID can mutate in humans, it can mutate in animals. Therefore, an animal with COVID could generate a new variant or subvariant and transmit it to humans.
In the worst case scenario, that new variant would be even more transmissible than Omicron’s currently dominant BA.5 subvariant and even more immunoevasive, perhaps even able to outwit antivirals like Paxlovid and hospital-administered monoclonal antibody treatments and outpatient settings.
The most likely culprit in such a scenario may be a bird, due to its migratory nature.
“Birds can rapidly migrate and spread new pathogens,” says Montgomery. “And there are definitely many cases in the literature of other coronaviruses affecting birds.”
Among the researchers keeping their eyes on the avian population: Dr. Raj Rajnarayanan, assistant dean for research and associate professor at the New York Institute of Technology campus in Jonesboro, Arkansas. He created and maintains several COVID-related data panels, including one on COVID in Animals, populated with data from GISAID, an international research organization that tracks changes in COVID and the flu virus.
While the majority of animal cases identified globally have been in mink, deer, and pets such as cats and dogs, Rajnarayanan recently noted that COVID has already crossed over into the avian population. The first two reported cases were recently identified in swans in China.
Omicron appears more likely to infect chickens and turkeys than the Delta variant, he says, adding that avian interbreeding could eventually have “big implications” such as new mutations, wide spread of the virus and impacts on the food supply.
“Everyone wants to focus on mammalian species,” he says. “Now the birds enter the scene. We want to monitor this much more closely.”
Rajnarayanan would like to see the US Department of Agriculture facilitate more frequent testing of farm animals. He also believes the agency should provide protective equipment to farmers to reduce the likelihood of transmission from farmers to farm animals and vice versa.
“We’re almost into our third year, we don’t want this to go on forever,” he says.
Veterinary and medical professionals must partner
As climate change continues, forcing animals and humans into more regular contact, side effects are likely to follow, whether it’s COVID, avian flu, or an as-yet-unknown pathogen of man, perhaps the next pandemic.
Montgomery advocates the “One Health” concept, which emphasizes that the health of people, animals, plants, and their shared environment are inexorably intertwined.
Veterinarians and doctors used to train together before the advent of the automobile, which caused doctors to move to big cities and hospitals and veterinarians to rural areas, where they were needed to care for farm animals, He says. Harvard used to house a veterinary school in addition to its medical school, and students trained together.
Such transdisciplinary collaboration is needed again if we are to finally get ahead of this pandemic and prevent the next one.
“We have to have the resources to not only think about human health, but to make sure we’re thinking about animal health,” he says, adding that humans often don’t care about animal diseases — until they come in. to the humans.
“Sometimes we don’t think about prevention or early mitigation or containment. We only react once something has entered the human population. Awareness is key here.”
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