Team researches whether humans can transmit COVID-19 back to bats
NEW YORK, N.Y.––A four-year-old Malayan tiger named Nadia, kept at the Bronx Zoo in New York City, and now four other times and three lions sharing the same facilities, may be evidence of asymptomatic human-to-animal transmission of COVID-19.
Alternatively, the tiger and lion illnesses may be evidence that the coronavirus responsible for approximately 12,000 human deaths in the city through April 25, 2020 is traveling by means other than human-to-human contact.
The Wildlife Conservation Society, umbrella for four New York City zoos and the New York Aquarium, on April 4, 2020 learned, and on April 5, 2020, disclosed that Nadia, “along with six other big cats — including Nadia’s sister Azul, two Amur tigers and three African lions — had all come down with a dry cough,” reported Live Science editor-in-chief Jeanna Bryner.
In Nadia’s case, COVID-19 was confirmed, using a testing method not normally used with humans. Confirmation that the four other tigers and three lions had COVID-19 came through further testing done two and three weeks later, according to Wildlife Conservation Society media releases.
Assuming all tigers in habitat were infected
Explained Wildlife Conservation Society chief veterinarian Paul P. Calle on April 6, 2020, via the www.ProMEDmail.org, the Program for Monitoring Emerging Diseases information network hosted by the International Society for Infectious Diseases, “The index case was one of two Malayan tigers, two Amur tigers, and three African lions who developed respiratory signs over the course of a week characterized by a dry cough and in some cases wheezing, but no dyspnea [labored breathing] or nasal or ocular discharge. Mild anorexia was noted in some cases. All of the cats are long term residents of the zoo, do not have chronic medical conditions, and there have been no new animal introductions to these groups for several years.”
“The source of infection,” Calle continued, “is presumed to be transmission from a keeper who, at the time of exposure, was asymptomatically infected with the virus, or before that person developed symptoms [i.e., pre-symptomatic]. The cats have received antibiotics and supportive care as needed, and all of the affected cats are doing well with no worsening of their clinical signs and daily gradual improvement.”
Pre-symptomatic or asymptomatic keeper?
But in a month of investigation, no such pre-symptomatic or asymptomatic keeper appears to have been identified.
A variety of other Bronx Zoo big cats, including snow leopards, cheetahs, a clouded leopard, an Amur leopard, a puma and a serval, have not shown COVID-19 symptoms, Calle said.
“It’s the first time, to our knowledge, that a [wild] animal has gotten sick from COVID-19 [passed] from a person,” Calle told Natasha Daly of National Geographic.
The Bronx Zoo has been closed to the public since March 16, 2020. Thus, to Calle, infection by an infected—but unknown—asymptomatic zookeeper is “the only thing that makes sense.”
But the Calle explanation may not make sense either.
“No documented asymptomatic transmission”
The World Health Organization advised on April 2, 2020 that asymptomatic transmission is essentially an unproven and relatively unlikely hypothesis, despite the prominence it has had in the public imagination as COVID-19 has spread worldwide, killing upward of 75,000 people.
“Some people can test positive for COVID-19 from one to three days before they develop
symptoms,” the World Health Organization acknowledged. Thus, “It is possible that people infected with COVID-19 could transmit the virus before significant symptoms develop,” the World Health Organization conceded.
Even so, the World Health Organization said, “It is important to recognize that pre-symptomatic transmission still requires the virus to be spread via infectious droplets or through
touching contaminated surfaces.
“An asymptomatic laboratory-confirmed case,” the World Health Organization stipulated, “is a person infected with COVID-19 who does not develop symptoms. There are few reports of laboratory-confirmed cases who are truly asymptomatic, and to date, there has been no documented asymptomatic transmission.”
Can U.S. brown bats become a COVID-19 reservoir?
William B. Karesh, who for nearly 20 years headed the Wildlife Conservation Society’s field veterinary health program, pointed toward another possible explanation for the Bronx Zoo tigers contracting COVID-19 during the March 31, 2020 meeting of the ad hoc World Animal Health Organization (OIE) working group “COVID-19: the human/animal interface.”
Karesh, who coined the term “One Health” in 2003 to describe the interdependence of healthy ecosystems, animals and people, is now executive vice president for health and policy at the organization EcoHealth Alliance.
Karesh is also president of the World Animal Health Organization (OIE) Working Group on Wildlife Diseases, and chairs the International Union for the Conservation of Nature Wildlife Health Specialist Group.
“In the U.S.A.,” Karesh mentioned, according to the meeting notes, “a research institute is planning on doing experimental infection studies in brown bats (which have a long range) to address the question, ‘If humans introduce SARS-CoV-2 infections into brown bats, could they become a reservoir?’”
What cat can resist playing with a sick bat?
Further, Karesh said, “The OIE project ‘EBO-SURSY’ is proposing to test 3,000 samples already collected from bats for hemorrhagic fever virus surveillance in West Africa for the presence of coronavirus, to assess whether precursor viruses to SARS-CoV-2 have been circulating.”
Transmission of COVID-19 appears to require a degree of sustained physical proximity that zookeepers and tigers would not normally have. Bronx Zoo tiger keepers are usually on the far side of Plexiglas barriers from the tigers. While the coronavirus causing COVID-19 can survive briefly on physical objects, Bronx Zoo tigers and keepers have minimal unprotected contact with the same physical objects, such as food or toys.
But the SARS-CoV-2 coronavirus appears to have originated among horseshoe bats, the most common bats in China. If humans can transmit the coronavirus back to common bat species in the U.S., such as brown bats, perhaps with blood-sucking mosquitoes or biting flies as an intermediary, what cat, even as large as a tiger, could resist the opportunity to play with a sick bat dropping into her habitat?
Five native bat species live wild at the Bronx Zoo
The Bronx Zoo, located alongside the Bronx River, is reputedly among the best bat habitats in New York City, offering a variety of old trees and buildings within which bats can roost, plus ponds and puddles potentially attractive to the flying insects that bats prey upon. A 2016 study by Wildlife Conservation Society and Fordham University researchers found five of the nine bat species native to New York state actually roosting within the Bronx Zoo grounds––and within the Central Park Zoo, Prospect Park Zoo, and Queens Zoo, as well.
If humans have introduced COVID-19 into the U.S. brown bat population somehow, the Bronx Zoo tigers may be the “sentinels” letting us know.
“We cannot simply shut down”
Not only the New York City zoos managed by the Wildlife Conservation Society, but most zoos, around the world, are meanwhile struggling to cope with the combination of economic stress caused by enforced closure with staffing shortages, as volunteers are kept out and the number of paid staff allowed to be on site is often limited.
The 56 accredited zoos in Germany on March 31, 2019 appealed to chancellor Angela Merkel, the German ministries for finance and the economy, and the 16 German state governors for a $110 million aid package to help them survive the COVID-19 shutdowns, Associated Press reported.
“Unlike other facilities, we cannot simply shut down our operations,” explained Leipzig zoo director Joerg Junhold. “Our animals still have to be fed and cared for. At the moment we are working without revenues,” Junhold said, “but with expenses at a consistently high level.”
“On the animal side, we’re business as usual”
In Australia, where most zoos are privately owned and operated, Billabong Zoo owner Mark Stone told the Australian Broadcasting Corporation mid-North Coast news team that, “Basically, with the animal side of things, we’re business as usual, which comes at a very high cost.”
Like Junhold in Germany, “We can’t close down the zoo and close down expenditure,” Stone said.
“After surviving the January 2020 bushfires,” the Australian Broadcasting Corporation report added, “the Mogo Zoo, south of Batemans Bay on the New South Wales south coast, has been forced to shut its doors less than a month after it re-opened. On New Year’s Eve, zoo staff evacuated smaller animals and stayed to defend the lion and tiger enclosures. All 200 animals were saved,” but with no revenue stream to keep them fed.
“Wildlife HQ on Queensland’s Sunshine Coast has seven koalas and nearly 200 other animals to care for, including a sun bear,” the Australian Broadcasting Corporation continued. “Chief executive Jarrod Schenk said his 12 staff, on being told about the closure, decided they would continue to help the animals without pay.”
34,000 eucalyptus leaves per day
The job includes collecting 34,000 eucalyptus leaves per day to feed the 17 resident koalas.
Reported Aamna Mohdin, for The Guardian, “It’s easy enough for Darren McGarry to socially distance from other people, as his home is in the Edinburgh zoo. McGarry, who has worked for the zoo for 34 years, can go an entire day without seeing someone,” during the shutdown of non-essential businesses throughout the United Kingdom.
“At Marwell zoo, based in Winchester, some staff have moved into empty cottages on site to continue caring for the animals,” Mohdin observed, reversing a longtime trend of zoo caretakers moving offsite.
Also, Mohdin said, “At Twycross zoo in Leicestershire, staff have moved to live on site, while London Zoo has repurposed its visitor lodges into temporary accommodation for essential staff.”
“Orangutans are skeptical”
At the Dudley Zoo in Dudley Castle, West Midlands, director Derek Grove told Mohdin that the keepers are doing their best to avoid altering the animals’ routines.
“We have orangutans and chimpanzees and they do get used to people and the way you work around them,” Grove said. “As soon as you start changing things, animals are not particularly pleased about it.”
Or, as Simon & Garfunkel sang, after a 1967 visit to the Bronx Zoo, “Orangutans are skeptical of changes in their cages.”
Derek Grove, however, did not admit to being, as the song alleged, “very fond of rum,” despite the widespread belief that alcohol is a COVID-19 panacea.