During the covid-19 pandemic, cases of coronavirus infection have been detected in pets such as cats and dogs, as well as in numerous animals that were in zoos, including gorillas and big cats. In the latter cases, infections have occurred even when caregivers wore personal protective equipment.
But what happened last December was even more disturbing, when the United States Department of Agriculture confirmed the first case of a wild animal infected with SARS-CoV-2 , the virus that causes covid-19. Researchers spotted an infected wild mink in Utah near a mink farm that was affected by a Covid-19 outbreak.
Are we transmitting the virus to wildlife? And if so, what implications would it have for both animals and us?
How do viruses jump from one species to another?
We are two scientists dedicated to the study of viruses in wildlife, and we are currently conducting a study that addresses the potential for transmission of SARS-CoV-2 from humans to domestic and wild animals.
Scientists call “spillover” the phenomenon that occurs when a virus jumps from one species to another. But fortunately these overflows are not common.
To infect a new species, a virus must be able to bind to a protein on a cell and penetrate that cell; and all this while trying to survive an immune system that has never been faced before. Then, while the virus tries to avoid antibodies and other antiviral agents, it must replicate in sufficient quantity to be able to be transmitted to the next animal.
This generally implies that the closer the contact between two species, the more likely they are to share viruses. The chimpanzee, which is the species most similar to man, can contract numerous human viruses and fall ill. Earlier this month veterinarians at the San Diego Zoo reported that the gorilla herd at the zoo was infected with SARS-CoV-2, which points to the possibility that the virus is capable of jumping from humans to our species closer.
Some viruses tend to stay in a single species or similar species, while others are capable by their very nature of making much larger intraspecies jumps. The flu, for example, can infect a wide variety of animals, from sparrows to whales. And, in the same way, coronaviruses are characterized by jumping between species every so often.
A key question is how many species and of what type SARS-CoV-2 could infect (and which of these species could help the virus to continue circulating).
The search for covid-19 in wildlife
In order for SARS-CoV-2 to spread from humans to wildlife, the animal must be exposed to a dose of the virus high enough to become infected.
The highest risk situations occur when there is direct contact with humans, such as when a veterinarian treats an injured animal. Contact between an infected person and their pet or contact between a COVID-19 infected with a farm animal also poses a risk, as these animals can act as intermediate hosts that allow the virus to spread to infect a wild species .
Another way that COVID-19 can be transmitted from humans to animals is through indirect infection, such as through sewage. Remains of covid-19 and other pathogens have been detected in this type of water, many of which are dumped without any treatment into natural areas where certain species of wild fauna, such as marine mammals, may be exposed to them. It is believed that this is how some California elephant seals contracted the H1N1 flu during the 2009 swine flu epidemic.
To find out if SARS-CoV-2 overflows are occurring, our team at Tufts University works with veterinarians and wildlife conservators across the United States to collect and analyze samples from the animals in their care. During this time we have analyzed samples from nearly 300 wild animals of more than 20 species, and so far none (from bats to seals to coyotes) have tested positive for COVID-19 in antibody tests or in swab samples. .
Our researchers have focused their activities of selective surveillance of wildlife in places where contagions from domestic animals had occurred. The first confirmed case of wild mink infection was detected while surveillance was being carried out near a mink farm where an outbreak had occurred. And although it is not yet clear how this wild mink contracted the coronavirus, the large number of infected minks and potentially infectious particles emitted by them make us speak of a high-risk area.
Bad for animals and bad for people
When a virus jumps into a new species it sometimes mutates to infect, replicate, and transmit more efficiently within the new animal. This process is called “host adaptation.” When a virus jumps to a new host and begins this adaptation process, the results are unpredictable.
In late 2020, when SARS-CoV-2 reached a mink farm in Denmark, it underwent a series of mutations that are rare when the virus attacks humans. Some of these mutations occurred in parts of the virus that most vaccines are designed to localize. And this did not happen just once, but the mutations occurred many times and independently in shoots produced in other mink farms. Although it is not yet clear what impact these mutations (if any) have on the development of the disease in humans, or even in vaccines, these are signs of host adaptation that could lead to to new variants of the virus; variants that could remain in animal hosts and reappear in the future.
Another risk is that SARS-CoV-2 could make animals sick. Environmentalists are especially concerned about endangered species like the black-footed ferret, a mink-like animal believed to be highly vulnerable to the virus.
Overflows from people to wild animals have already occurred in the past. In the late 20th century the Ebola virus leapt from humans to great apes and had devastating consequences for these endangered species. And more recently, a human respiratory virus has been detected that affects threatened populations of mountain gorillas, and has also caused numerous deaths.
But perhaps the biggest risk to humans is that the overflow could cause the coronavirus to be stored in new animal species and in regions that have not been affected so far. This could mean that new covid-19 outbreaks could reappear in the future.
This month an article was published showing that this has already happened on a small scale in mink farms in Denmark, where the virus passed from humans to animals and then back again to humans.
Although our team has not found evidence of COVID-19 cases in wild animals in the United States, there is conclusive evidence of frequent overflows in dogs, cats and some animals that live in zoos. The finding of infected wild minks confirmed our fears. Detecting the first case in a wild animal with covid-19 was alarming, but not surprising.
Jonathan Runstadler, Professor of Infectious Disease and Global Health, Cummings School of Veterinary Medicine, Tufts University y Kaitlin Sawatzki, Postdoctoral Infectious Disease Researcher, Tufts University
Este artículo fue publicado originalmente en The Conversation. Lea el original.
