“A tiger at a US zoo has tested positive for the coronavirus, becoming the first animal to contract COVID-19,” it announced in April 2020.
The story follows Nadia, a 4-year-old Malaysian tigress, and six other tigers at the Bronx Zoo who contracted COVID early in the pandemic, apparently after being cared for by a symptomatic zookeeper.
This was the first in a steady stream of stories about animals who, like most of us, have contracted COVID. According to the US Centers for Disease Control and Prevention, animals include:
- Pets like cats, dogs, ferrets and hamsters.
- Zoo animals like lions, tigers, leopards, otters, jackals, hippos and manatees.
- A mink that lives on farms.
- Wildlife including many white-tailed and mule deer, black-tailed marten and giant anteater.
COVID is a “zoonotic” disease transmitted from animals to humans or vice versa. It is thought to have passed from a bat, pangolin, or raccoon dog to humans, possibly through an intermediary such as a pet (although the controversial “lab leak” hypothesis has not been completely ruled out).
Like COVID, the 2009 H1N1 “swine flu” pandemic is believed to have been caused by the mixing of flu strains between North American and European pigs. West Nile virus, which originates from arthropods and is transmitted by mosquitoes, was established in New York City in 1999 and has since become endemic in the United States. in monkeys but is thought to have originated in rodents.
Animals apparently started the COVID-19 pandemic, as many others have, but their role in it was not lost until later. The pathogen now circulates, crosses, and sheds again in both populations, even though such events are relatively rare. Like humans, animals continue to shape pandemics as new variants and subvariants mutate with their skin, fur, and fur before trying to enter the wider population.
Scientists are watching for signs of what’s to come in the animal world.
The host is the host
Scientists have recently begun tracking the spread of COVID in animals on publicly available bulletin boards. By the end of last month, 704 cases of COVID-19 had been diagnosed in 39 countries and 27 species of animals worldwide by the Wildlife Conservation Society and Australian researchers at the University of Veterinary Medicine in Vienna.
Among those discovered:
- In the United States, 117 cats and 110 dogs have been infected
- Minks are one of the animals most commonly identified with COVID. In addition to 159 American mink in Greece alone, about 150 mink have been identified in Spain and 250 in Lithuania.
- Most animals were asymptomatic or experienced respiratory symptoms. Minks can die.
- Omicron subvariants are the most common strains identified in animals, but Delta cases have also been documented.
The risk of contracting COVID from animals is low, says the doctor. Mary Montgomery is a clinical educator in the infectious diseases department at Harvard-affiliated Brigham and Women’s Hospital in Boston.
But it is real. According to a recent study, COVID may have entered humans from animals — possibly in a few patients from multiple animal encounters in late 2019 — and can re-enter animals through humans in a process scientists call “zoonotic transmission.”
Just as COVID can mutate in humans, it can also mutate in animals. Thus, an animal with COVID can produce a new variant or subvariant and reinfect humans.
In a worst-case scenario, that new variant is more transmissible and more immune-evasive than the current dominant Omicron subvariant BA.5, possibly even outperforming antiviral drugs such as Paxlovide and monoclonal antibody treatments given in hospitals and outpatient settings.
In such a scenario, the most likely culprit would be birds because of their migratory nature.
“Birds can move and spread new pathogens quickly,” Montgomery says. “And there are many cases of other coronaviruses affecting birds in the literature.”
Researchers monitoring bird populations include: Dr. Raj Rajnarayanan, associate dean for research and associate professor at the New York Institute of Technology campus in Jonesboro, Ark. It creates and maintains a series of COVID-related dashboards filled with data from GISAID, an international research organization that tracks the evolution of the COVID and influenza virus.
Although most of the animals detected globally have been in mink, deer and domestic animals such as cats and dogs, Rajnarayanan noted that recently, COVID has crossed into bird populations. The first two cases were recently identified in swans in China.
Chickens and turkeys appear to be more likely to be infected than the Omicron Delta variant, he said, adding that avian crossover could eventually have “major consequences” such as new mutations, the spread of the virus and impacts on the food supply.
“Everyone wants to focus on mammal species,” he says. “Now birds come into the picture. We want to monitor this more carefully.”
Rajnarayanan wants the USDA to promote more frequent inspections of farm animals. He also believes the agency should provide protective gear to farmers to reduce the chance of transmission from farmers to farm animals and vice versa.
“We’re almost in our third year — we don’t want to keep doing this forever,” he says.
Medical and veterinary professionals should be partners
As climate change continues to force animals and humans into constant contact, the spread and spillover of—whether it’s COVID, bird flu, or an as-yet-unknown human pathogen—may be the next pandemic.
Montgomery advocates the concept of “One Health,” which emphasizes that the health of humans, animals, plants, and their shared environment are interconnected.
Veterinarians and doctors practiced together before the advent of automobile-driven cities, which resulted in doctors moving to larger rural hospitals and vets, where farm animals had to be cared for, he said. Harvard used to have a veterinary school in addition to the medical school, and students practiced together.
Such transdisciplinary collaboration is needed if we are to get through this pandemic and prevent the next one.
“We have to have the resources to make sure we’re thinking about animal health, not just human health,” he says, and people don’t have to worry about animal diseases until they get to humans.
“Sometimes we don’t think about prevention or early mitigation or containment. We only react when something enters the human population. Awareness is important here.”
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