• P.K. Peterson

Preventing Animal Spillovers of Microbes to Humans

“The human race is challenged more than ever before to demonstrate our mastery, not over nature but of ourselves.” - Rachel Carson

“Collaboration operates through a process in which the successful intellectual achievements of one person arouse the intellectual passions and enthusiasms of others.”

- Alexander von Humboldt

Six months ago, two burning questions about the cause of this pandemic and the connection between animals and humans were: 1) in what animal species did the coronavirus originate? and 2) what other animals can be infected that could serve as a reservoir of the virus and thus perpetuate the pandemic? Somewhat surprisingly, we still don’t have a conclusive answer to either. We are rapidly getting much closer, however, to understanding the role of animals. The goal of this Germ Gem is to provide an update to the April 15 Germ Gem post “COVID-19: What Animal Is to Blame?’ by discussing further the involvement of other animal species in this pandemic.

The hunt for the origin of SARS-CoV-2. All researchers remain in agreement that COVID-19 is a zoonotic infection and that the causative agent, SARS-CoV-2, jumped or spilled over from an animal to a human somewhere in or close to Wuhan, China in late 2019. All the evidence also continues to point to the Chinese horseshoe bat as the primary source of SARS-CoV-2. Nonetheless, pinning the zoonotic source of this infection down to everyone’s satisfaction has proved very difficult. In no small measure, this is due to a lack of transparency on the part of the Chinese government that has fueled political disputes and several conspiracy theories. The good news is that on November 5, the World Health Organization (WHO) released details of its mission with China to carry out a global investigation into the origin of SARS-CoV-2.

According to the article “The WHO is hunting for the coronavirus’s origins. Here are the details,” published in theNational Geographic on November 6, the WHO refers to this investigation as “business as usual.” It has engaged a group of expert disease detectives that have worked on similar hunts to do this search. The WHO recruited Linfa Wang, a biologist and the director of the Programme in Emerging Infectious Diseases at Duke-NUS Medical School in Singapore, to follow the SARS-CoV-2 thread from animals to humans. Wang, referred to as “The Batman,” is credited with tracing SARS-CoV-1 (the coronavirus that caused the 2003 pandemic of severe acute respiratory syndrome) from an intermediate host called a civet cat to humans and then to the Chinese horseshoe bat as the primary source of that coronavirus. Multiple research groups already have reached the conclusion that while SARS-CoV-2 also originated in bats that an unidentified intermediary animal host served as a reservoir for the virus and played a key role in the jump to humans, much as did civets (carnivorous catlike animals) in igniting the SARS pandemic. The search for the intermediary animal host (or reservoir of the virus) is part of the WHO mission.

What animals are known to harbor SARS-CoV-2? In April the evidence was highly suggestive that pangolins are the main reservoir of the novel coronavirus. (Pangolins are scaly, totally harmless creatures that have the dual misfortune of being the world's most trafficked mammal, as well as being sold in wildlife markets in China.) By April, it was also found that a small handful of pets (dogs and cats but also a tiger in the Bronx Zoo) were infected with SARS-CoV-2. Humans infected these animals in a process known as reverse zoonoses (zooanthroponoses). Since then a number of infected dogs and cats with coronavirus-like symptoms have been found in Europe. And in the August Annals of Science article “Did Pangolins Cause the Coronavirus Pandemic?” spillover expert David Quammen suggests that researchers need to look elsewhere for the animal reservoir.

In April, researchers in the Netherlands also reported two outbreaks of coronavirus infections in mink farms. A farm worker who had COVID-19 introduced the virus into the mink population. By June, the coronavirus had ripped like wildfire through 10 additional mink farms. Mink were not, however, the only animals affected. Feral cats roaming the farms—and stealing the mink’s food—were found to be infected as well. More important, genetic and epidemiological sleuthing reported that at least two farm workers had caught the virus from mink. Even though just two of the Netherland’s cases were linked to the farms, the Dutch government ordered the culling of mink in the farms.

What’s happening in Denmark? Except for the initial spillover event from a still unknown animal species, mink are the only animals known to have passed the coronavirus to humans. Thus, the Danish government moved aggressively on November 6 by ordering more than a quarter million Danes into lockdown in a northern region of Denmark where a mutated variation of SARS-CoV-2 had infected mink being farmed for their fur. Taking no chances, the Danish authorities also ordered the culling of all 15 million mink bred in Denmark’s 1,139 mink farms. (Denmark is the world’s largest exporter of mink fur.)

Mink certainly have the potential to become a reservoir for future viral transmissions to humans. And the eruption of this mutated strain of SARS-CoV-2 in Danish mink “hits all the scary buttons” and should be watched closely. To help assuage panic, the WHO pointed out that viral mutations happen all the time and that there’s no evidence that this variant (which infected 12 people so far) is more dangerous than the original pandemic strain. Many experts believe that this mutated strain neither poses a higher risk to humans nor that the mutated viruses would evade vaccines against SARS-CoV-2 once they are made available. It also seems unlikely that mink are the intermediary host (reservoir) that propelled the virus into humans in Wuhan in late 2019.

What would Alexander von Humboldt say? Most scholars recognize Alexander von Humboldt as the founder of the field of ecology. (In America, many would give this honor to Rachel Carson whose book The Silent Spring, published in 1971, triggered the environmental movement.) The central concept of ecology is that “everything is connected”: animals, including humans, plants, and inanimate components of our environment, such as water, air, and constituents of soil. We Homo sapiens have ignored this fact for far too long.

In my April 15 Germ Gem post on what animal is to blame for the COVID-19 pandemic, I made the case that we, Homo sapiens, are primarily responsible for the pandemic. As a species we have forgotten that everything is connected and have mistreated both wildlife and our environment. We need to regain an ecological perspective in how we approach life. Such an ecological perspective, coupled with an understanding of the value of collaborations, should inform all programs that are working on solutions to COVID-19 as well as the prevention of future pandemics. Perhaps then Homo sapiens will be able to claim credit for resolving this pandemic rather than just accepting the responsibility of having contributed in a major way to its emergence.

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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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