The role of “animal reservoirs” in the spread of Covid is still being studied but evidence of zoonosis, or the virus jumping from animals to humans, is growing and scientists are concerned this new frontier could potentially spawn dangerous and difficult to monitor mutants.
While there is no consensus about the origins of the SARS-CoV-2 virus, many scientists believe it likely jumped from bats to humans, either directly or through another species being sold live in a market in Wuhan, China.
Some experts also forward the theory that the highly mutated Omicron variant, which caused a deluge of cases globally, including in India, emerged from animals, potentially rodents, rather than an immune compromised human. “As the virus multiplies in infected hosts, it can mutate slightly, and the worry is that over time, minor genomic tweaks in hundreds or thousands, if not millions, of animals, could eventually add up to changes that make the virus more contagious or deadlier in people, or able to evade treatments and vaccines,” US-based public health expert Amita Gupta told PTI in an email interview.
Smaller mutations of SARS-CoV-2 in animals may add up to make the virus more contagious or deadlier in people, said the chief of the Division of Infectious Disease, and professor of medicine at Johns Hopkins University School of Medicine.
The role of wildlife in the global epidemiology of SARS-CoV-2 may currently be insignificant but the Covid pandemic is a stark reminder of the close connect between human and animal health. Although the number of people infected with coronavirus variants evolved in animals has not been quantified yet, the evidence of zoonosis is growing.
Last week, the Centers for Disease Control and Prevention (CDC) confirmed that at least four people in Michigan, US, were infected with a version of the coronavirus observed mostly in minks during the first year of the pandemic.
Farmed minks and pet hamsters have been shown to be capable of infecting humans with the virus and a potential case of transmission between white-tailed deer and a human in Canada is currently under review.
Flagging the concern, the World Health Organisation (WHO) last month said the introduction of SARS-CoV-2 to wildlife could result in the establishment of animal reservoirs of the virus.
“Current knowledge indicates that wildlife does not play a significant role in the spread of SARS-CoV-2 in humans, but spread in animal populations can affect the health of these populations and may facilitate the emergence of new virus variants,” the WHO said in a statement In addition to domestic animals, free-ranging, captive or farmed wild animals such as big cats, minks, ferrets, deer, lions and great apes have been observed to be infected with SARS-CoV-2.
According to veterinarian Gaurav Sharma, a successful reservoir host is one where the virus can get established in the animal population with the help of efficient intra-species transmission. Such animals reintroduce the virus into the human population.
“During the replication of virus in new host it undergoes adaptation process which can lead to some mutation in wild type virus due to which new variants of virus can emerge,” Sharma, from the Centre for Animal Disease Research And Diagnosis (CADRAD), in Bareilly, Uttar Pradesh, told PTI “In the face of decreasing community transmission among human populations due to various control measures, the significance of a potential animal reservoir among wild mammals increases. In such a case, the implications of spillback to humans from animals would be more significant,” he said.
The researcher noted that this may also lead to the emergence of new variants as the virus adapts in the new animal host. This was seen in mink farms in Denmark where transmission of the virus from humans to minks led to the establishment of the virus in the new host and, in turn, the emergence of a mink-associated variant circulating in humans.
“This finding prompted culling of minks in Dutch mink farms in early June 2020. This mink derived lineage touted as cluster 5 variant and showed evidence of immune escape,” he said.
Though the magnitude of concern is difficult to gauge at this point it is a cause of concern to humans due to various reasons, agreed epidemiologist Dharmaveer Shetty.
“If there are animal reservoirs, it becomes relatively more difficult to eradicate the virus, it becomes relatively costlier to monitor the virus, and the probability of getting new variants increases as well,” Shetty told PTI.
An increased number of host species (animals) that the virus can infect can lead to an increased number of individuals amongst the expanded host base that can support the virus.
“This, in turn, will lead to increased multiplication of the virus due to the presence of an increased number of susceptible host individuals causing rise in chances and number of mutations in different conditions,” Shetty said.
Sharma added that the emergence of such variants affects the transmission dynamics of the virus in humans and also may reduce the effectiveness of the currently used diagnostics and vaccines.
According to a recent yet-to-be peer reviewed study, the first potential case of a deer passing the novel coronavirus to a person has been reported in Canada. It also identified highly mutated clusters of SARS-CoV-2 genomes in white-tailed deer, underscoring the potential for deer to act as an animal reservoir for the virus.
Shetty said these results point towards the possibility of deer to human transmission but it is not yet definitive.
“Only after further study and surveillance will we get a better idea about the actual risk of animals transmitting new variants to humans,” he said.
To manage this latest frontier in Covid fight, Shetty said it is important to monitor the virus across host animals to know how the virus is evolving and transmitting.
“… Update the vaccine accordingly, maintain herd immunity of the human population by vaccination using regularly updated vaccines, and take preventive measures,” Shetty said.
Gupta noted that globally there is an unprecedented amount of data being captured about animal health and the dangers are still being studied.
“We, therefore, want to continue to support and strengthen our health systems and approaches which work to understand human, animal, environment interactions and data are important to support so we can optimise our preparedness for Covid and other emerging infectious diseases,” she added.
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