How wide is the spread of Covid in animals and what are the risks to humans?


Two studies have shown that the high rate of Covid-19 infection in wild deer in the United States has once again raised concerns about the spread of the virus in animal populations.

As the survey results released this month were released, more and more reports of pets and captive animals infected with the new crown virus continued to emerge. Earlier this month, the Lincoln Children’s Zoo in Nebraska lost three rare snow leopards to the disease.

Although the Sars-Cov-2 virus causes few or no symptoms in most non-human animals, some scientists worry that wild animals may become the host of infection—and possibly viral mutations—may be transmitted to humans. It may also threaten endangered species.

How wide is the spread of Covid in animals?

As of the end of October, the World Organization for Animal Health (OIE) has recorded 598 Covid outbreaks in starters, affecting 14 species in 30 countries. Almost all involve captive animals that are in close contact with humans-Danish farmed minks are the most affected.

Map showing the Covid-19 outbreak in animals

No one knows the prevalence of Covid in wild animals because there are very few tests. Two new studies of white-tailed deer in the United States showed for the first time widespread infections in wild populations.

A paper published by USDA scientists on PNAS found antibodies against Sars-Cov-2 in 40% of wild white-tailed deer in four states in the United States at the beginning of this year.

A second study led by Penn State University but not yet published directly detected the virus in 80% of samples of the same species in Iowa through PCR. This is the most abundant deer in North America, with an estimated 30 million deer.

“We are all very surprised and confused by the high rate of deer testing positive,” said Katrina Wilgart of the Department of Disease Dynamics at the University of Cambridge, who was involved in the Penn State University research. “Genetic and geographic data indicate that infected humans will have multiple spills and then spread widely from deer to deer.”

Which species are most susceptible to infection?

Sars-Cov-2 originated in bats and may have been transmitted to humans through a still unknown animal intermediary. Comprehensive evidence from natural transmission and laboratory experiments shows that the virus can infect most mammals, but unlike influenza, it does not infect birds.

The susceptibility between species varies widely and is unpredictable. “We are very fortunate that research has shown that the main farm animals-pigs, cattle and sheep-are very resistant to infection, which is different from white-tailed deer,” said Keith Hamilton, head of preparation and recovery at the World Organisation for Animal Health. Say. “If they are also highly sensitive, it will be a disaster.”

Ken Smith, a professor of pathology at the Royal College of Veterinary Medicine in London, said cats, especially large cats such as lions, tigers and leopards, seem to be more susceptible to infections than dogs.

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

What can people do to prevent the spread of coronavirus between animals and humans?

Although the only clear evidence of the transmission of the coronavirus from animals to humans was during the intensive outbreak in mink in Denmark last year, experts advise people to avoid contact with pets when their pets or their animals show Covid symptoms.

Alastair Ward, head of the Department of Biological Sciences at the University of Hull in the United Kingdom, said that widespread infections in deer indicate that hunters should take precautions when handling carcasses, such as wearing gloves.

Vaccines can be used to protect animals from Covid. Zoos in the United States are vaccinating more and more species with jabs developed specifically for non-human recipients. Vulnerable big cats are a popular target.

Zoetis, an animal health company spin-off from Pfizer, has developed a vaccine based on the Sars-Cov-2 spike protein, which can be applied to multiple species. Farmed mink are being vaccinated on a large scale, but the Covid vaccine is usually not suitable for pets.

Can animals become permanent hosts of infections​​–and sources of new mutations?

The study of American white-tailed deer worries biologists. Graeme Shannon, a zoologist at Bangor University in Wales, said: “Although experimental work has shown that infected deer are often asymptomatic, the spread of diseases in wild animals has a considerable impact on human health.”

“These findings have raised concerns that deer may be the host of Sars-Cov-2. Not only is this easy to infect a large number of animals, but more worryingly, it will also be transmitted to humans,” he added. “Any reinfection of the wild animal host may complicate our long-term efforts to fight and suppress this disease.”

A potential threat is that as the virus spreads in the animal host, more dangerous strains may appear and then enter the human body, although this is not a foregone conclusion. Evolution that optimizes the fitness of other species does not necessarily make the virus more effective in infecting humans. In November 2020, new variants appeared in mink and were transmitted to humans, but the results proved that none of the variants is abnormally disseminated or toxic in humans.

The Sars-Cov-2 variant found in deer in Iowa is the same as the variant that was spread in the population at that time. But it may be too late for the virus to evolve in these animals.

Another question is whether Covid will disappear from the deer or continue to spread between them indefinitely. Suresh Kuchipudi, the lead author of the Pennsylvania State University paper, called for more evidence.

“The study emphasizes the urgent need to implement an urgent monitoring plan to monitor the spread of Sars-Cov-2 in deer and other susceptible wildlife species, and take measures to mitigate potential spillover effects,” he said.

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