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  • Writer's pictureP.K. Peterson

COVID-19: What Animal Is to Blame?

“The better I get to know men, the more I find myself loving dogs.”

Charles de Gaulle

Like a majority of other emerging infections, COVID-19 is a zoonotic infection, that is, it was transmitted from animals to humans. A question that immediately came to the minds of doctors and scientists last December when COVID-19 erupted in Wuhan China was, “Where did this virus come from?” While there is not yet a definitive answer to which animals are involved, as I discuss below the puzzle is already fairly complete. But a lack of transparency by the Chinese government on exactly where and how SARS-CoV-2, the cause of COVID-19, got its start has slowed research on this issue.

Despite some loose ends, however, it is already abundantly clear that to see the primary animal to blame for COVID-19, you need merely to take a look in the mirror. As Lucretius said in the 1st century BC: “What is food for one man, may be bitter poison to others.” If some members of our species didn’t have a taste for and deal in the trading of wild animals, it is highly unlikely that any of the coronavirus pandemics of the 21st century would have emerged.

You’ve undoubtedly heard something about other zoonotic infections—HIV/AIDS, West Nile virus infection, Ebola, Zika, avian and swine flu—to name just a few. But it’s the emerging coronavirus infections that have impacted our species most severely in the 21st century.

Animals connected to coronavirus infections in humans. Like COVID-19, severe acute respiratory syndrome (SARS), emerged in China in 2002. And in both cases, a wild animal market was quickly implicated as ground zero for these devastating global infections. In the case of SARS, a wild animal market in Guangdong province that sold civets, small cat-like mammals, appeared to be the origin. (Civets were found to harbor the virus and were quickly culled.) In Wuhan, a seafood market that sold a number of wild animals was rapidly implicated.

As is shown in the table above, the Chinese horseshoe bat is thought to be the primary animal reservoir of the coronaviruses that caused two of the 21st century coronavirus pandemics (SARS and COVID-19). Bats also seem most likely to be the primary reservoir of MERS-CoV, the cause of Middle East respiratory syndrome (MERS) that emerged in Saudi Arabia in 2012. Unsurprisingly , camels appear to be a secondary animal reservoir of MERS-CoV. While civets were considered a secondary reservoir of SARS-CoV, in the case of SARS-CoV-2, pangolins — scaled anteaters that are the most widely illegally trafficked mammal in the world—served as a secondary reservoir of this coronavirus.

Although there are unique features of each of the coronavirus pandemics, a common denominator of at least two of them is wild animal markets. Wet market” is a term widely used across parts of Asia to describe markets that sell meat, fish and perishable goods, as opposed to dry markets that sell nonperishable goods.

Wildlife species sold at such live animal markets are diverse – including bats, civets, bamboo rats, snakes, birds, and many other species, alongside domestic animals such as chickens, pigs, dogs, etc. The conditions of these markets with live animals stacked closely together in stressful and unsanitary conditions increase the chance that viruses can ‘spillover’ from one animal host to another and to humans.

It is clear, however, that it is only the live wildlife markets, where wildlife harvested both illegally and legally are stacked closely together in cages and slaughtered and sold for food or medicinal purposes, that pose the biggest threat to humans. Mingling of wild animals and humans provides an opportunity for viruses to crossover or “jump” from animals to humans.

Reverse zoonoses (zooanthroponoses). While almost all of the attention on infectious agents transmitted from one species to another has focused on crossovers from animals to humans, we cause our share of suffering among other animal species. In a review article published in PLOS One in 2014, evidence of human-to-animal transmission of bacteria, viruses, and parasites (reverse zoonoses) was documented on every continent except Antarctica. To me, the transmission of the bacterium that causes tuberculosis is most striking, and of the animals humans can afflict, the devastation in elephants is most heartbreaking. (Just imagine Packey, a senior and beloved pachyderm in the Oregon Zoo in Portland, who lost 1,400 pounds in two weeks when he became infected by the tubercle bacillus.)

Like other reverse zoonoses, concern has been raised about potential human transmission of SARS-CoV-2 to other animals. Given their genetic similarity to Homo Sapiens, orangutans and other great apes appear to be under the greatest threat, and although there have been no confirmed cases, precautionary measures are being taken in zoos and other facilities housing these animals.

Tigers (and other cats) can catch SARS-CoV-2. On April 5, a Malayan tiger at the Bronx Zoo in New York City tested positive for the virus, and six other big cats were reported to be exhibiting symptoms consistent with the illness. It is thought the tiger acquired the virus from an asymptomatic zookeeper. Several domestic animals had previously tested positive for SARS-CoV-2, including a Pomeranian and a German Shepherd in Hong Kong, and a domestic cat in Belgium.

So if you develop COVID-19, the CDC recommends avoiding cuddles, kisses, sharing food, and having other close contact with your pet to avoid passing the virus on to them.

Additional reasons why Homo sapiens is to blame. The extinction of species has gone on since life began almost four billion years ago. However, because of human activities, the rate at which species go extinct has accelerated dramatically.

The alarming loss of animal and plant species was described in detail in 2019 in the United Nations report Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. In this report we are told that because of humans, as many as one million plant and animal species are now at risk of extinction, posing a dire threat to ecosystems all over the world.

The reasons behind the extraordinary extinctions of animal and plant species are complex, and often not completely understood. But climate change, the destruction of habitats, and the emergence and spread of pathogens all appear to be involved.

Preservation of biodiversity. On an optimistic note, on March 11, 2020, the World Economic Forum launched a “COVID-19 Action Platform” to fight the COVID-19 pandemic. “The private sector has an essential role to play in combating this public health crisis through their expertise, innovation and resources,” said Tedros Adhanom Ghebreyesus, Director-General of the World Health Organization. “We call on companies and organizations around the world to make full use of this platform in support of the global public health response to COVID-19.”

Protecting the natural world is a fundamental tenet of the Action Plan, as are collaborations with other organizations that are dedicated to epidemic and pandemic preparedness. While the plan, as laid out in their website is a valuable starting point, meaningful “action” must be taken now for prevention of the emergence of new zoonoses.

While it is good that China has temporarily closed down its live wild animal markets, it is crucial that the ban be made permanent and that other Asian countries follow suit. On a related note, another top priority should be putting a stop to illegal trafficking of wild animals. As Jan Vertefeuille, senior advisor, advocacy, at the World Wildlife Fund stated, “We know what needs to be done to help prevent future zoonotic pandemics, and we call on decision-makers everywhere to immediately and urgently take these steps to halt biodiversity loss and reduce the chances of another zoonotic pandemic.”

COVID-19 is the third coronavirus to hit us this century. In four short months - months that seem like years - everyone on Earth has suffered the consequences of this zoonosis. We know now that pandemics such as this are inextricably linked to how we mistreat other animals! And, while it is not yet clear when this pandemic will end, it is abundantly clear that we can’t tolerate another - the time for strong, coordinated action is long overdue.

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Main Page images courtesy of Shuxian Hu, MD. Dr. Hu is a scientist in the Neuroimmunology Research Laboratory at the University of Minnesota.

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