A potential COVID-19 reservoir on the trail in New York state’s Harriman Park/Wikimedia Commons

Add whitetail deer to the growing list of animals other than humans that can become infected with the COVID-19-causing SARS-CoV-2 virus.

The deer, according to a team of scientists from around the U.S., “are highly susceptible to SARS-CoV-2 infection and can transmit the virus through direct contact as well as vertically from doe to fetus.”

The group’s study was posted Monday at MedRxiv. It has yet to be peer-reviewed, but the team includes researchers from a number of highly respected research entities, including the U.S. Department of Agriculture’s National Bio and Agro-Defense Facility,  the Department of Diagnostic Medicine/Pathobiology at Kansas State University, the Louisiana Animal Disease Diagnostic Laboratory and Department of Pathobiological Sciences at Louisiana State University and the Icahn School of Medicine at Mount Sinai, New York.

To date, there have been no documented cases of deer passing SARS-CoV-2 to humans as has happened with mink. Researchers in the Netherlands made that discovery in the spring and reported it in a peer-reviewed paper in Science in March. 

“More work must be done to understand whether there is a risk that mustelids (such as mink, ferrets and badgers) may become a reservoir for SARS-CoV-2,” they warned at the time.

The finding of deer infected with SARS-CoV-2, some of which developed COVID-19, only adds to that concern.

“White-tailed deer are amongst the most abundant, densely populated, and geographically widespread wild ruminant species in the United States,” the U.S researchers noted. “(And) human interaction with white-tailed deer has resulted in the occurrence of disease in human populations in the past.”

A plague of deer

They are now so common in urban and suburban New York that the state has compiled a list of “overabundance hotspots.”

“People encounter deer on a daily basis now in places where a few decades ago they were never seen, and the highest deer densities in the state can be found in urban and suburban areas,” the report says. “Urban and suburban deer overabundance is most common in the parts of the state that are most developed and have the most restrictions on hunting, including Long Island, New York City and Westchester, Onondaga, Monroe and Erie counties.”

Six counties on Long Island or including New York City lead the list of the deadliest places for COVID-19 in that state, which is one of the hardest hit in the nation. Westchester ranks seven, according to the Worldometer COVID-19 tracker; Erie is eight, Monroe, 10, and Onondaga, 13. 

High rates of human infection increase the likelihood deer could pick up SARS-CoV-2 from humans, and given the speed at which the virus has been developing new variants, scientists worry that a large number of infected animals of any species could develop yet another variant they could transfer back to humans.

Transfer has already happened on a small scale with the mink in the Netherlands.

“Recent large-scale SARS-CoV-2 surveillance efforts in animals and humans have found evidence of reversezoonosis (human-animal) resulting in natural infections in companion animals, farmed mink, primates and large cat species in several countries,” the latest study noted. “The source of infection in these incidences are likely infected pet-owners and animal care workers on farms and at zoos. Additionally, SARS-CoV-2 has demonstrated its ability to rapidly mutate and cross back into human populations, giving rise to new variants of interest or concern.”

The U.S. researchers echoed the March observation of the Dutch in pointing out that “these situations exemplify the critical need to evaluate potential host species for SARS-CoV-2 which may act as reservoirs for future, secondary zoonotic events.

“Furthermore, this work demonstrates the need for more intensive, focused surveillance efforts on high-risk
animal populations, such as farmed and wild white-tailed deer and mule deer populations, as well as farm, wildlife and
zoo workers, in order to identify new animal-derived SARS-CoV-2 variants which may evade current mitigation strategies.

“Human interaction with infected wild animal populations could provide avenues for un-checked spillover back into human populations and spontaneous resurgence of SARS-CoV-2 infections with new animal-adapted SARS-CoV-2 variants, as already experienced with mink.”

Alaska experience

Alaska readers might here recall the “bird flu” (avian influenza) scare of 2005 that resulted in a small army of biologists flocking to Western Alaska to swab the butts of waterfowl arriving from Asia to see if they had been infected.

They sampled almost 17,000 birds between May 2006 and March 2007 and reported finding “low pathogenic avian influenza viruses…detected in 1.7 percent but no highly pathogenic viruses were found.”

It was eventually concluded that the virus of concern – H5N1 –  does not transmit easily between people. Most infections were linked to close contact with domestic poultry in Bangladesh, China, Egypt, India, Indonesia, and Vietnam where the pathogen is considered endemic, according to the U.S. Centers for Disease Control (CDC).

It was, however, thought considerably more contagious in 2005 when then-President George W. Bush warned of the possibility of a global pandemic on the order of the Spanish flu of 1918-1919.

“…If history is our guide, there’s reason to be concerned,” he said. “In the last century, our country and the world have been hit by three influenza pandemics, and viruses from birds contributed to all of them.

“The first, which struck in 1918, killed over half a million Americans and more than 20 million people across the globe. One-third of the U.S. population was infected, and life expectancy in our country was reduced by 13 years.

“The 1918 pandemic was followed by pandemics in 1957 and 1968 which killed tens of thousands of Americans and millions across the world.”

Ahead of the game

Little could anyone know at the time, but the pandemic of which Bush warned would arrive 15 years later in the form of a pathogen different from influenza but equally deadly – SARS-CoV-2.

As of this writing, the World Health Organization (WHO) reports almost 208 million people around the globe have been infected, and the virus is blamed for nearly 4.4 million deaths although it might be years before the actual death count is known.

India, which lists an official death toll of 432,000, is believed to have grossly undercounted the fatalities. Elsewhere there are debates about how many people died of COVID-19 and how many died with COVID-19 given that many of the dead were already suffering from serious medical conditions at the time of their deaths.

Of the 255,508 people in this country whose deaths were linked to COVID-19 between Feb. 1, 2020 and Dec. 5, 2020, the CDC reported that in only 6 percent of the cases was COVID-19 identified as the sole cause of death.

In 94 percent of cases, other medical conditions were mentioned as well, often two or more. COVID-19 has manifested itself as almost two different diseases – a particularly deadly one for the old and/or unhealthy and a more flu-like illness for the young and fit.

Fitness, along with vaccination, has been shown to be protective against the virus, and both together are arguably the best defense in that the efficacy of vaccines has been slipping in the wake of the new Delta variant.

Vaccine boosters are in the works. Meanwhile, a special scientific panel has advised the government of the United Kingdom that it should expect the virus to endure.

The Scientific Advisory Group for Emergencies (SAGE)  called eradication “unlikely.”

“In addition to the oldest human endemic CoV (NL63), in the last 150 years there have been five known coronavirus incursions from animals into humans. Of these, three ended up as human endemic pathogens (229E, OC43 & HKU1) and two have caused limited but severe disease (SARS-CoV & MERS-CoV). Therefore, CoV zoonosis appears a common consequence of human proximity to animals,” SAGE added.

Wild white-tailed deer appear to pose a risk of becoming one of those animals, the U.S. researchers looking for possible SARS-COv-2 reservoirs reported in their study.

“Furthermore, commercially farmed deer is a growing industry in the U.S.” they added.

“Human interaction with white-tailed deer have resulted in the occurrence of infectious diseases such as brucellosis or tuberculosis in human populations in the past. Recently, white-tailed deer fawns were demonstrated to be susceptible to experimental SARS-CoV-2 infection. Also, it was recently reported that serosurveillence studies conducted in 2021 show that 40 percent of wild white-tailed deer tested across the midwestern U.S. were positive for SARS-CoV-2 neutralizing antibodies although it is unclear at this time if these results are caused by
SARS-CoV-2 exposure or cross-reactivity of a yet unidentified closely related coronavirus infection in deer.”

Research is ongoing to determine if there is a closely related coronavirus common to deer, but the lack of SARS-CoV2 antibodies in blood collected from deer prior to 2019 would seem to argue against that possibility.

The study was done before the Delta variant became dominant in the U.S., and it is thus unknown how it might affect deer. But SARS-CoV-2 spreading into animals other than humans only makes it that much harder to control.