Tiger at Bronx Zoo Tests Positive for COVID-19

In what appears to be the first known case ever reported in the world, a four-year-old Malayan tiger at the Bronx Zoo in New York City has tested positive for SARS-CoV-2, the virus causing the current COVID-19 pandemic. Even more concerning is the fact that six other big felines are exhibiting symptoms associated with the illness, as reported by the US Department of Agriculture.

Scientists are now rushing to investigate what other animal species could also be susceptible to the novel coronavirus.

The Curious Case of Nadia the Tiger

Cats, both domestic and wild, are vulnerable to the feline coronavirus, and it has also been reported that cats might infect each other. However, prior to this case at the Bronx Zoo, the same fact hadn’t been established for SARS-CoV-2. The zoo had been closed for visitors since March 16, and because of this, Paul Calle, chief veterinarian for the Bronx Zoo, suspects that the tiger most probably contracted the virus from an infected but asymptomatic zookeeper:

It’s the first time, to our knowledge, that a [wild] animal has gotten sick from COVID-19 from a person. It’s the only thing that makes sense.

Four-year-old Malayan tiger Nadia developed a dry cough in late March, and blood samples were sent for testing for SARS-CoV-2 to the New York State Diagnostic Laboratory at Cornell University and to the University of Illinois College of Veterinary Medicine Veterinary Diagnostic Laboratory on April 2. Nadia’s sister, three African lions and two Siberian tigers have also reported of coughs and loss of appetite, but they haven’t been tested yet. As of now, the seven cats are under veterinary care and the Wildlife Conservation Society, the non-profit that operates the Bronx Zoo, expects them to recover, however, cautioning that they don’t know for sure how the disease might advance in animals.

Zookeepers across the country are now making additional arrangements to protect great apes, since the latter are highly susceptible to catching respiratory illnesses from humans. Experts have also warned that these species might be particularly vulnerable to COVID-19. Dan Ashe, president of the American Association of Zoos and Aquariums (AZA), which endorses more than 200 zoos in the Unites States, including the Bronx Zoo, stated that they helped distribute material cautioning about the potential of coronavirus transfer from humans to felines, and about increasing safety measures, such as wearing masks and goggles to safeguard animals, and also maintaining a distance of six feet wherever possible.

However, there is still concern about the substandard roadside zoos around the US. The majority doesn’t have veterinarians on staff, and diagnostic tests, if needed, are also unlikely. During a time where maintaining human-human and animal-human distance is of utmost importance, the cub-petting offered by these zoos is extremely worrying.

John Goodrich, chief scientist and Tiger Program director at Panthera (global big cat conservation organization), is apprehensive about wild tiger populations:

Big cats like tigers and lions are already facing a litany of threats to their survival in the wild. If COVID-19 jumps to wild big cat populations and becomes a significant cause of mortality, the virus could develop into a very serious concern for the future of these species.

Dr. John Williams, chief of the Division of Pediatric Infectious Diseases at the University of Pittsburgh Medical Center Children’s Hospital of Pittsburgh, has examined coronaviruses for decades. According to him, tigers also caught SARS-CoV, the correlated coronavirus that caused severe acute respiratory syndrome (SARS) during the 2002-2004 outbreaks. However, it is quite unsettling that the Bronx tiger most probably became infected with a fairly low dose of SARS-CoV-2. While none of the zoo’s other big cats, such as cheetahs, snow leopards an Amur leopard is showing any symptoms, it is yet to be established whether tigers and lions are more prone to coronavirus than other species.

The Novel Coronavirus: Infecting Humans and Animals

Coronaviruses have thrived in animals for thousands of years. SARS-CoV-2, the novel coronavirus at the center of the ongoing pandemic, has been highly successful in jumping from human to human. Just four months into the outbreak the virus has infected more than 1.36 million people worldwide. However, the case of Nadia provides evidence that the novel coronavirus can also hijack animal cells. Scientists claim that the disease originated in Chinese horseshoe bats and via an intermediary animal made its way to humans. SARS-CoV-2 enters cells by binding to a cell-surface protein called ACE-2, which is found on most animal cells. COVID-19 is hence known as a zoonotic disease, it jumps from an animal to humans.

Since the ongoing pandemic, many domestic animals have tested positive for COVID-19, including a Pomeranian, a German shepherd, and a domestic cat. So, according to experts, it’s not unexpected that exotic animals such as lions and tigers can also catch the disease. Even though the cat showed symptoms of respiratory problems and had high levels of the virus in its vomit and feces, researchers still aren’t sure whether the cat was sick from COVID-19 or some other related illness.

Jacqui Norris, a veterinary scientist at the University of Sydney in Australia, commented

These pets were living with infected human owners, and the timing of the positive result demonstrates human-to-animal transfer. Virus culture on these pets was negative, meaning that an active virus was not present.

In a series of experiments highlighted by Nature, scientists kept infected animals in cages next to three uninfected animals and found that, in a single case, the virus had jumped from cat to cat. However, no outward symptoms of illness were seen. Dogs, on the other hand, seem to be more resistant. Five three-month-old beagles were inoculated with SARS-CoV-2 and kept with two healthy dogs. A week later, the healthy dogs didn’t have the virus in their system, but their bodies had generated an immune response. What must be noted is that these experiments were conducted in a controlled setting using high doses of the coronavirus which is not reflective of real-life scenarios. Nevertheless, felines do appear to be more vulnerable to infection.

Are Animals Now a Threat to Humans for Transmitting COVID-19?

It’s been established that SARS-CoV-2 can jump from humans to humans, animals to animals, and now as with the Malayan tiger, from human to felines. But can the virus be transmitted from a cat to its caregiver? Experts agree it is highly unlikely.

According to the United States Department of Agriculture (USDA) and the Centers for Disease Control and Prevention (CDC), there is currently no evidence to suggest that domestic or wild animals can transfer the virus to humans.

Dr. Sarah Caddy, veterinarian and a Clinical Research Fellow at the University of Cambridge, says:

The bottom line is that there is no evidence that any cat, large or small, can transmit the virus back to humans.

However, for the safety of our animals, Professor Jacqui Norris, from the Sydney School of Veterinary Science at the University of Sydney, warns

If a member of the household becomes sick with Covid-19, they should be isolated from all members of the household, pets included.

Until more research into the virus is conducted, experts suggest we should follow some basic guidelines. Contact between an infected person and animals should be minimized. Proper hygiene measures must be enforced, such as hand washing before and after handling animals or pets. Also, kissing and sharing food with the latter should be avoided.

We may not conclusively know the origin story of SARS-CoV-2, but we do know that coronaviruses can inhabit all manner of species; whether they cause disease in all cases is a question that requires further investigation. As of now, epidemiologists are working to figure out which species can harbor the virus to better understand where it might lie dormant, and how likely it is to jump back to humans and cause a future outbreak.

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