It is a widely held belief that coronavirus does not spread from animals to humans. The virus that first infected people in China late last year came from an animal source, still unidentified, and later spread from person to person, as other coronaviruses had done in the past. Some animals, including cats, tigers and dogs, have picked up the new coronavirus from people, but there hasn't been a documented case of animals spreading it back to humans.
But, coronavirus outbreaks at mink farms in Spain and the Netherlands have scientists reconsidering the possibilities. The latest was an outbreak at the Spanish mink farm near La Puebla de Valverde, a village of 500 people, discovered after seven of the 14 employees, including the owner, tested positive in late May, according to reports. Two other employees got infected even after the operation was shut down.
As the Dutch government and researchers have found, outbreaks among the minks on the farms in the Netherlands and Spain likely started with infected workers, while it also is plausible that some workers later caught the virus back from the minks. Professor Wim van der Poel, a veterinarian who studied the same, told news agency AP that the virus strain in the animals was similar to the one circulating among humans. "We assumed it was possible that it would be transmitted back to people again, and that's what appeared to have happened with at least two of the infected workers."
What do the World Health Organisation (WHO) and other authoritative sources claim?
Animal-to-human transmission was considered a rarity bordering on the impossible. According to the World Health Organisation (WHO): "Several dogs and cats [domestic cats and tigers] in contact with infected humans have tested positive for COVID-19. In addition, ferrets appear to be susceptible to the infection. In experimental conditions, both cats and ferrets were able to transmit infection to other animals of the same species. However, there is no evidence that these animals can transmit the disease to humans and spread COVID-19." However, the WHO also noted that minks raised in farms have also been detected with the virus. "In a few instances, the minks that were infected by humans have transmitted the virus to other people. These are the first reported cases of animal-to-human transmission."
But WHO's Dr Maria Van Kerkhove said at a news conference last month that such transmission was very limited. "This gives us some clues about which animals may be susceptible to infection and this will help us as we learn more about the potential animal reservoir of [the virus]," she said.
The US CDC, in its website, has noted: "At this time, there is no evidence that animals play a significant role in spreading the virus that causes COVID-19. Based on the limited information available to date, the risk of animals spreading COVID-19 to people is considered to be low. More studies are needed to understand if and how different animals could be affected by COVID-19."
What are its implications?
Earlier studies, like one published in the New England Journal of Medicine, have highlighted the ease of transmission between domestic cats, noting there is a public health need to recognise and further investigate the potential chain of human–cat–human transmission. "This is of particular importance given the potential for SARS-CoV-2 transmission between family members in households with cats while living under “shelter-in-place” orders. In 2016, an H7N2 influenza outbreak in New York City cat shelters highlighted the public health implications of cat-to-human transmission to workers in animal shelters. Moreover, cats may be a silent intermediate host of SARS-CoV-2, because infected cats may not show any appreciable symptoms that might be recognised by their owners," according to the study.
A Lancet Microbe study has noted the importance of not minimising the risk of human-to-animal transmission. It said that the probability of a new reservoir species should be considered, adding that there is a need to implement early surveillance and precautionary mitigation measures on different species ."Once SARS-CoV-2 circulates more widely beyond humans, it will be challenging to trace natural transmission between species because the viral genome is essentially identical in humans, and existing epidemiological methods of contact tracing are equipped to identify transmission between humans to interrupt it. Assessing these risks includes reviewing our ability to isolate, protect, or contain animals in domestic, agricultural, and wildlife settings. Domestic species whose population numbers are sufficient to act as a reservoir include cats and dogs, which is consistent with the case reports noted earlier, and studies showing or predicting infectivity."
“We know that these viruses are capable of mutating,” said Peter Rabinowitz, a physician who directs the University of Washington Center for One Health Research, which is studying the virus in household pets, told Washington Post. “There could be changes in the virus, and these human-animal transmission events could play more of a role in the future, and we have to be more vigilant.”
Richard Ostfeld, a researcher at the Cary Institute of Ecosystem Studies in Millbrook, New York, told AP: "With the evidence for farmed mink-to-human transmission, we definitely need to be concerned with the potential for domesticated animals that are infected to pass on their infection to us."
-Inputs from agencies