Snow leopard (image courtesy Pixabay)
[Editor's note: This story originally was published by Real Clear Science.]
By Ross Pomeroy
Real Clear Science
Over the past two years, the COVID-19 Pandemic has slammed the United States, killing 958,300 as of February 18th, roughly one in every 340 Americans. Yet for all the pain, suffering, and hardship the pandemic has caused for Americans, snow leopards have had it worse.
Snow leopards are a remarkable species of big cat that dwell in cold, mountainous regions of central Asia. An estimated 4,080-6,590 snow leopards remain in the wild, making the species highly vulnerable to extinction. As such, about 600 leopards are kept in accredited zoos around the world to help ensure the species' survival, 250 of them in the United States. At least five of these American-kept leopards have now died from COVID-19, for a death rate of one in 50, about seven times worse than what Americans have endured.
The latest death was 11-year-old Rilu at the Miller Park Zoo in Illinois. Initially infected in late November, he succumbed to COVID-related pneumonia in early January. Before Rilu, there was two-and-a-half-year-old Baya at the Great Plains Zoo in South Dakota, who passed just four days after showing symptoms. Perhaps the most heartbreaking loss occurred at the Lincoln's Children's Zoo in Nebraska. All three of the institution's beloved snow leopards – Everest, Makalu and Ranney – died of COVID-19 complications about a month after contracting the disease.
COVID-19 infections have been reported in other captive big cats as well, including Malayan tigers at a zoo in Virginia, African lions, Amur tigers, and jaguars at the St. Louis Zoo, and numerous large felines at the San Diego Zoo. In general, they show similar symptoms to us: lethargy, labored breathing, coughing, decreased appetite, and runny nose. Big cats likely contract COVID-19 from their keepers.
Besides the five snow leopards, a 13-year-old male lion at the Honolulu Zoo in Hawaii also died. There have neem no other published big cat deaths in the U.S.
Felines are highly susceptible to COVID-19 because – like humans – the cells of their respiratory tracts express a lot of the enzyme ACE2 on their membranes, and their ACE2 enzyme is very similar to ours. SARS-CoV-2, the virus that causes COVID-19, binds to ACE2 to gain access to cells. The more ACE2 that cells have, the more they are vulnerable to infection. Various studies conducted across the globe have probed house cats for antibodies against SARS-CoV-2, a sign of prior infection. Anywhere from five percent to a quarter have likely contracted the virus at some point, almost certainly from their human companions.
Luckily for cats, they don't express nearly as much ACE2 in their lung cells as humans do, which reduces their risk of severe disease. Most cats don't even show symptoms to a COVID-19 infection. Why, then, does this trend not seem to hold for snow leopards? Scientists aren't sure, but there are a couple possibilities. First, the five snow leopard deaths may just be unlucky, a statistical artifact. Alternatively, leopards' lung cells may express more ACE2 than their cat cousins. Lab studies are needed to shed light on this speculation.
The American drug company Zoetis, which makes medicines and vaccines for animals, produces an animal-specific COVID-19 vaccine. U.S. zoos are now immunizing their inhabitants, hopefully ending the danger to snow leopards.
[Editor's note: This story originally was published by Real Clear Science.]
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