Chinese health experts have called for intensive monitoring of the coronavirus in wild animals, warning that its spread between different species risks further dangerous variants.
A number of animals have been found to be susceptible to Covid-19, and the potential for ongoing mutations of the virus in these animals, such as mink, poses "a huge threat to public health if they transmitted back to humans", wrote the report's lead author Gao Fu, head of the Chinese Centre for Disease Control and Prevention.
"It is necessary to carry out large-scale Sars-CoV-2 screening for terrestrial and marine wildlife, especially those susceptible ones ... so as to formulate further prevention and control strategies," said Gao and co-author Wang Liang of the Chinese Academy of Sciences said in a perspective published in the China CDC's weekly bulletin.
Such work could also "provide more clues" about the origins of Covid-19, they said.
Eleven species have so far been reported to be infected by Sars-CoV-2 in real-world circumstances - including tigers, gorillas, snow leopards and mink - according to Gao and Wang. Another 14 species have been identified as able to be infected via lab experiments.
But these could just be the "tip of the iceberg" for susceptible animals, the authors warn, as there has been limited laboratory screening of different species for infection risks, including of marine mammals.
The spread of the virus through white-tailed deer in the United States, also shows a risk that the virus could mutate and spread from deer to other animals before passing back into people, according to the authors.
"Since Sars-CoV-2 is going wild, many other wild animals would also be infected with Sars-CoV-2 via direct or indirect contact with wild white-tailed deer," they wrote, adding that measures like the large-scale culling of farmed mink in the Netherlands are not possible with wild animals.
A recent US government study of wild deer in several states between January 2020 and March 2021 showed that around one-third of the deer had traces of past infection, though there had been no reports of illness among the deer. Animal health authorities in August said they were working to further evaluate any risks and urged game hunters to maintain hygiene when handling deer meat.
Other governments have sought to mitigate risks from animal exposures. In Finland, this week authorities cleared mink farmers to use an experimental coronavirus vaccine on the animals, which are bred for fur.
China has reported infections in pets, but not in the nearly 80,000 wild animals, livestock and poultry tested following the outbreak as part of efforts to identify animals that may have been involved in the virus's initial jump to people.
Some scientists have said that infected animals may have been missed and further, targeted testing is needed to understand if this was how the virus - thought to originate in a bat - first spread into people.
In a separate correspondence on the origins of the virus published in The Lancet medical journal last week, Gao and other CDC officials called for international scientists to investigate potential early infections in humans and animals around the world.
They pointed to evidence suggesting the Middle East Respiratory Syndrome virus had been circulating in camels for at least two decades before a human case was identified.
"Comprehensive genomic studies in animal species that are susceptible to the virus are necessary to identify the natural or intermediate hosts," the authors wrote, adding "open-mindedness and close international cooperation are pivotal for tracing the origins of any viruses".
China has said it supports further investigations into the origins of Covid-19, but rejected what it views as a politically motivated World Health Organization proposal for next stage work, instead pushing for the focus to shift outside its borders.
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