How common is Covid in animals and what are the risks to humans?

Two studies showing high levels of Covid-19 infection among wild deer in the US have raised concerns about the virus spreading through animal populations.

The findings, published this month, come as there are increasing reports of Covid in pets and animals in captivity. Lincoln Zoo for Children in Nebraska lost three rare snow leopards sick earlier this month.

Although the Sars-Cov-2 virus causes little or no symptoms in most non-human animals, some scientists are concerned that wild animals could become reservoirs for the infection. – and possibly virus mutations – can be transmitted back to humans. It can also threaten endangered species.

How common is Covid in animals?

The World Organization for Animal Health, known as OIE, has recorded 598 outbreaks of Covid in animals affecting 14 species in 30 countries as of the end of October. Almost all have involved animals. In captivity in close contact with humans – with domesticated mink in Denmark being the most affected.

Map showing outbreaks of Covid-19 in animals

No one knows how widespread Covid is in wildlife because there is so little testing. Two new studies of white-tailed deer in the US are the first to show widespread infection in wild populations.

A piece of paper published in PNAS by scientists at the US Department of Agriculture found antibodies to Sars-Cov-2 in 40% of wild white-tailed deer across four US states earlier this year.

A second study, led by Penn State University and yet to be published, detected the virus directly via PCR in 80% of samples taken in Iowa from the same species – the most abundant North American deer. with an estimated 30 million individuals.

Katriina Willgert of the University of Cambridge’s Disease Dynamics Unit, who was involved in the Penn State study, said: “We were all surprised and baffled by the positive rate of giraffe testing. “Genetic and geographic data suggest multiple waves of transmission from infected humans and then widespread deer-to-deer transmission.”

Which species are most susceptible to infection?

Sars-Cov-2 originated in bats and may have migrated to humans through an as yet unidentified animal intermediary. Combined evidence from natural transmission and laboratory experiments suggests that the virus can infect most species of mammals, although unlike influenza, it is not contagious. infect birds.

Susceptibility varies substantially and unpredictably between species. “We are very fortunate that studies show that key farm animals – pigs, cattle and sheep – are resistant to resistance,” said Keith Hamilton, OIE’s head of preparedness and resilience. infection is quite good, unlike the white-tailed deer. “It would be a disaster if they were also very susceptible to infection.”

Ken Smith, professor of pathology at the Royal Veterinary College in London, says cats, especially big cats such as lions, tigers and leopards, appear to be more sensitive than dogs.

A snow leopard
A snow leopard. Big cats appear to be more susceptible to Covid than dogs © Cindy Ord / Getty Images

What can people do to prevent coronavirus from spreading between animals and people?

Although the only clear evidence of coronavirus being transmitted from animals back to humans came during the Danish concentration outbreak among weasel Last year, experts advised people to avoid contact with pets when they or their animals were showing Covid symptoms.

Alastair Ward, head of the department of biological sciences at the University of Hull in the UK, said the discovery of such widespread infection in deer suggests that hunters should take precautions such as wearing gloves when handling deer. handling animal carcasses.

More and more vaccines are available to protect animals from Covid. Zoos in the United States are implanting a growing range of species with spikes developed specifically for non-human recipients. Vulnerable big cats are preferred targets.

Zoetis, the veterinary company spun off from Pfizer, has developed a vaccine based on the Sars-Cov-2 mutant proteins that can be adapted to multiple species. Pet ferrets are being vaccinated on a substantial scale, but a Covid vaccine is generally not available for pets.

Can animals be permanent reservoirs of infection – and a source of new mutations?

Studies of American white-tailed deer have worried biologists. Graeme Shannon, a zoologist at Bangor University, Wales, said: “Although experimental work shows that infected deer tend to be asymptomatic, transmission of the disease is in animals. wildlife has a significant impact on human health.

“The findings raise concerns that deer could be a reservoir for Sars-Cov-2. Not only can this easily infect large numbers of animals, but more worryingly, it will spread back to humans,” he added. “Any reinfection from wildlife reservoirs could complicate our long-term efforts to fight and contain the disease.”

One potential threat is that as the virus spreads in an animal reservoir, more dangerous strains may arise and then migrate to humans, although that is not conclusive. Physically optimized evolution for another species will not necessarily make the virus more effective at infecting humans. New variants emerged in ferrets and spread to humans in November 2020, although none turned out to be unusually transmissible or virulent in human populations.

The Sars-Cov-2 variants identified in the Iowa deer were the same as those circulating in the human population at the time. But it may not be time for viruses to evolve in these animals.

Another concern is whether Covid will disappear from the deer herd or continue to pass indefinitely between them. Suresh Kuchipudi, lead author of the Penn State paper, appealed for more evidence.

“This study highlights the urgent need to implement surveillance programs to monitor the spread of Sars-Cov-2 in deer and other susceptible wildlife species, and to suggest ways to improve these outcomes,” he said. measures to minimize potential spillover effects.

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