Does COVID-19 infect wildlife? We test species, from bats to seals to find out


During the COVID-19 pandemic, researchers have found coronavirus infections in pet cats and dogs and in several zoo animals, including big cats and gorillas. These infections even occurred when staff used personal protective equipment.

More worryingly, in December, the US Department of Agriculture confirmed the first case of a wild animal infected with SARS-CoV-2, the virus that causes COVID-19. Researchers have found an infected wild mink in Utah near a mink farm with its own outbreak of COVID-19.

Do humans transmit this virus to wildlife? If so, what would that mean for wild animals and humans too?

How viruses jump from one species to another

We are two scientists who study viruses in wildlife and are currently conducting a study on the potential for transmission of SARS-CoV-2 from humans to domestic and wild animals.

When viruses move from one species to another, scientists call it overflow. Fortunately, the overflow does not happen easily.

To infect a new species, a virus must be able to bind to a protein on a cell and enter the cell while avoiding an immune system that the virus has never encountered before. Then, as a virus tries to avoid antibodies and other antiviral attackers, it must replicate at a volume high enough to be passed on to the next animal.

This generally means that the more closely related two species, the more likely they are to share viruses. Chimpanzees, the species most closely related to humans, can catch and get sick from many human viruses. Earlier this month, veterinarians at the San Diego Zoo announced that the zoo’s gorilla troop was infected with SARS-CoV-2. This indicates that it is possible for this virus to pass from humans to our close relatives.

Some viruses tend to stay in a single species or in closely related species, while other viruses naturally seem to be more capable of skipping large species. The flu, for example, can infect a wide variety of animals, from sparrows to whales. Likewise, coronaviruses are known to regularly jump between species.

The question of how many and which species can be infected with SARS-CoV-2 – and which might be able to support the continued circulation of the virus – is important.

Finding COVID-19 in Wildlife

In order for the SARS-CoV-2 spillover from humans to wildlife to occur, an animal must be exposed to a sufficiently high viral dose to be infected.

The most risky situations occur in direct contact with humans, such as when a veterinarian is caring for an injured animal. Contact between a sick person and a pet or farm animal also poses a risk, as the domestic animal could act as an intermediate host, possibly transmitting the virus to a wild animal.

Another way COVID-19 could spread from humans to animals is through indirect infection, such as sewage. COVID-19 and other pathogens can be detected in waste streams, many of which end up being dumped, untreated, in environments where wildlife like marine mammals may be exposed. It is believed that this is how California elephant seals became infected with the H1N1 flu during the swine flu pandemic in 2009.

To study if the SARS-CoV-2 overflow is occurring, our team at Tufts is partnering with licensed veterinarians and wildlife rehabilitators across the United States to collect samples and test the animals they have. keep. Thanks to the project, we have tested nearly 300 wild animals of more than 20 species. So far, none – from bats to seals to coyotes – have shown evidence of COVID-19 through swabbing or antibody testing.

Other researchers have launched targeted wildlife surveillance in places where captive animals have been infected. The first confirmed infection in a wild mink was found during surveillance near an infected mink farm. It is not yet clear how this wild mink caught the coronavirus, but the high density of infected mink and potentially infectious particles have made it a high-risk location.

Bad for animals, bad for humans

When a virus infects a new species, it sometimes mutates, adapting to infect, replicate, and transmit more efficiently in a new animal. This is called host adaptation. When a virus moves to a new host and begins to adapt, the results can be unpredictable.

At the end of 2020, when SARS-CoV-2 jumped into farmed mink in Denmark, it acquired mutations that were rare in humans. Some of these mutations have occurred in the part of the virus that most vaccines are designed to recognize. And this did not happen once: these mutations have appeared independently on several occasions in mink farms. While it is not yet clear what impact, if any, these mutations may have on human disease or the vaccine, these are signs of host adaptation that could allow new variants of the virus to persist. and reappear in host animals in the future.

Another risk is that SARS-CoV-2 can cause disease in animals. Environmentalists are particularly concerned about endangered species like the black-footed ferret, which is closely related to mink and considered very susceptible to the virus.

The overflow from man to wildlife has already happened. At the end of the 20th century, the Ebola virus passed from humans to great apes and had devastating consequences for these endangered animals. More recently, a human respiratory virus has been detected in endangered populations of mountain gorillas and has also caused deaths.

But perhaps the greatest risk to humans is that the overflow could lead to the creation of a reservoir by the coronavirus in new animals and regions. This could provide opportunities for the reintroduction of COVID-19 in humans in the future. This month, researchers published a paper showing that this had already happened on a small scale with human-to-human transmission from mink to human in mink farms in Denmark.

While our team has not found any evidence of COVID-19 in wildlife in the United States at this time, we have seen compelling evidence of a regular fallout on dogs and cats and some zoo animals. The discovery of the infected wild mink confirmed our fears. Seeing the first wild animal with natural COVID-19 is alarming, but sadly, not surprising.

Coronavirus cases detected in farmed mink in Poland

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