In the epicenter of the United States' coronavirus outbreak, even the lions and tigers started coughing.
On Sunday, the Bronx Zoo announced that one of its majestic Malayan tigers tested positive for COVID-19, the respiratory disease caused by the new coronavirus. Meanwhile, three other tigers and three lions (who were not tested) were also sick and hacking. The zoo said an infected zookeeper transmitted the virus to the exotic cats, which became a well-publicized instance of the insidious microbe jumping between animal species.
Though it might sound strange that large, dominant cats have fallen ill to the same parasite that has severely sickened and killed people around the globe, infectious disease experts aren't surprised. Animals often pass diseases to other animals. And some 75 percent of emerging infectious diseases in humans come from other animals species, known as "zoonotic diseases."
For example, the SARS outbreak in 2003 (also a coronavirus) spread from bats, to another animal, to humans. MERS jumped from camels to humans. The dog flu that swept through greyhounds in 2004 came from horses. This latest coronavirus likely originated in bats. There are untold numbers of viruses living in wild animals that could potentially jump from species to species. It's just a matter of time.
"Jumps between species are often the reason why we get pandemics," said Rebecca Dutch, a virologist and chair of the Department of Molecular and Cellular Biochemistry at the University of Kentucky College of Medicine. (The grim Bubonic Plague, for instance, comes from a bacterial pathogen transferred by fleas).
"The next ones are out there," Dutch added, noting that we already know of many bat coronaviruses. Another one, at some unknown point, may again jump to another species, perhaps eventually to humans.
Of course, zoonotic viruses can't jump to all species. The virus has to be able to match with the proteins on an animals' cells, somewhat like a key fitting a lock. For example, mice cannot currently catch this new coronavirus, officially called SARS-CoV-2. "There are species that aren't infected, but some species that are," said Dutch. Some viruses can only live in one species and can't jump to other animals, like smallpox (which was eradicated) and measles in humans.
Unfortunately for humans, SARS-CoV-2 made the jump to people, likely having first hopped between an intermediary creature, perhaps a pangolin. And now the virus has jumped to big cats in the Bronx, if not elsewhere. But, critically, it's unknown if the microbe can jump from cats back to humans.
"We have no evidence that a cat can infect a human right now," said Siobain Duffy who researches the evolution of viruses at Rutgers University. Though, there's some evidence cats can spread the virus to other cats. (It's also unknown how easy it is for a cat to catch coronavirus from people, but if it were easy, epidemiologists would have probably picked up on this source of infection by now.)
From Dr. Paul Calle, Bronx Zoo chief veterinarian; "The COVID-19 testing that was performed on our Malayan tiger Nadia was performed in a veterinary school laboratory and is not the same test as is used for people.
— Bronx Zoo (@BronxZoo) April 6, 2020
Image: WCS
Once a virus, like a coronavirus, gets in humans, then there's good potential for an epidemic, or, at worst, a pandemic. That's because the virus isn't just infecting an isolated population of animals in a forest somewhere. Now it's hopping on 600-mph commercial airliners.
"They’re getting around the world," said Dan Janies, a professor of bioinformatics at the University of North Carolina at Charlotte who researches the genetics of zoonotic viruses.
In the 2003 SARS outbreak, for example, the virus first likely jumped from bats to another unknown animal to humans, but eventually started passing between civets cats and humans in Guangdong, China. The virus was discovered in cages in a restaurant where raccoon-like civets were served. Infected people then traveled. "Then it went to humans around the world," said Janies, who found the SARS virus originated in bats.
"Lots of viruses are out there."
"We rapidly spread [viruses] because we travel so well," added Dutch. "We give them all sorts of chances for new places to go."
Although scientists know many infectious diseases in humans come from other animals, like bats, we're not vigilantly researching all the coronaviruses in bats and where they could potentially jump. It's not a research priority — until it is. "It’s not a medical problem when it's hanging out in bats," said Janies.
As for now, the new coronavirus — that likely jumped from bats, to another animal, to humans, and now Bronx Zoo cats — has resulted in lions and tigers that are sick, but doing alright.
"All of our tigers and lions are doing well and continue to improve daily," said Dr. Paul Calle, the Bronx Zoo Chief Veterinarian.
The same can't be said for humans, where U.S. hospitals are filled with severely sick people, many who need machines to breathe.
This coronavirus — with a vaccine a year or so away at best — already foreshadows the next inevitable viral leap from animals to humans. So society must prepare, emphasized Dutch. "We need to be more forward-thinking," she said. This means preparing to rapidly test and then isolate infected people — which the U.S. failed to do for this pathogen. It also means preparing potential antiviral drugs that can be tested and rapidly deployed when the next epidemic, or pandemic, hits.
It will.
"Lots of viruses are out there," said Dutch. "The question is, when will it enter the human population?"
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