The next phase in monitoring wild animals for COVID-19

When it comes to how wild animals contract and spread COVID-19, there are far more questions than answers. For example, infectious disease experts know that white-tailed deer can become infected with the virus. But how are they getting it? From our trash maybe, or is it an environmental source like groundwater? And if that's the case, why do deer across the U.S. test positive more frequently than other forest mammals, like raccoons?

It's these questions and more that researchers from the Runstadler Lab at Cummings School of Veterinary Medicine at Tufts University hope to answer under a new two-year contract from the U.S. Department of Agriculture (USDA).

"The main question for this study is simply, can wild animals serve as a potential reservoir host for SARS-CoV-2 in a public health context? If the answer is yes, then there are lots of questions within that," said Jonathan Runstadler, D.V.M., Ph.D., chair of the Department of Infectious Disease and Global Health at Cummings School.

In some respects, this work will build upon research that originally started in 2020 during the height of the COVID-19 pandemic, when researchers in his lab began investigating the potential for SARS-CoV-2 transmission between humans and domestic and wild animals using samples gathered from a network of wildlife rehabilitators in Massachusetts as well as patients at Foster Hospital for Small Animals and Tufts Wildlife Clinic. Those efforts resulted in a handful of discoveries, including one that proved to be the bridge to this next research project.

For one thing, they found a high prevalence of dogs and cats that had antibodies against SARS-CoV-2, but not the actual virus, which means that transmission occurred at some point, but the animal had since recovered. (Yes, dogs and cats can get COVID-19.) Conversely, they also found that ferrets that were exposed to the COVID-19 virus for an extended period showed no evidence of contracting the virus, even though ferrets can become infected with respiratory viruses like influenza.

In addition, Kaitlin Sawatzki, Ph.D., a post-doctoral researcher in the Runstadler Lab, was part of a team that showed how a tiger at a Tennessee zoo became infected with SARS-CoV-2 and passed the virus to two other Malayan tigers at the zoo.

"We're seeing if we can detect the presence of the SARS-CoV-2 virus in the samples, though that's a bit like looking for a needle in a haystack," said virologist and senior scientist Wendy Puryear, Ph.D., manager of the Runstadler Lab. "You have to test the right animal at the right time to pick up the actual virus. So, we're also looking for antibodies against the virus as evidence that the virus was there."

At first, the researchers were testing for the virus and antibodies in blood samples, and they wanted to see if they could detect antibodies off swab samples instead. Not only are swab samples easier to collect, but the researchers were already using swab samples for avian influenza testing. After extensive investigation, Sawatzki determined that they were indeed able to detect SARS-CoV-2 antibodies off swab samples across a diversity of species. The lab is now using this method as a standard way to conduct SARS-CoV-2 surveillance testing for any type of mammal.

"The USDA wants to conduct more thorough surveillance sampling than has been done previously to know if and when the virus gets into species that we previously had not known could be infected," Runstadler says. "They've funded our project and others in hopes of obtaining a good representation of different species and geography that could potentially serve as reservoirs for this health threat to animals or humans."

Collaboration with wildlife rehabilitators

For years, the team has worked with a network of wildlife rehabilitation facilities throughout Massachusetts to test animals that come into their care for SARS-CoV-2 and avian influenza, and Puryear says they already have a pipeline of samples coming in for screening. In the past, rehabilitation centers may have taken a blood or swab sample only if an animal was symptomatic for avian influenza or SARS-CoV-2.

The team is hoping to widen the scope going forward to sample a broader array of animals that come into a center, regardless of outward clinical symptoms. And they hope to work with more rehabilitators throughout New England and down the Atlantic coast to bolster the number of animals tested.

If they find a particular species repeatedly comes up positive, they may develop what's known as a cell line, or a repository of cells from that host that can be maintained in a suitable environment indefinitely. Through the cell line, they can study more closely the ability of the virus to infect those cells and how the host cells respond. If it can, that better informs which animals may be susceptible to SARS-CoV-2 and why, on a molecular and genetic level. However, setting up a cell line requires a tissue sample from an animal.

"No animal will be euthanized for this research," Puryear says. "But if there is an animal that dies due to an illness or injury shortly after coming into care, then there's a short window of time to get tissue from that animal and put it into the right conditions to develop a cell line. Should that scenario arise, we are putting the pieces in place to be able to respond quickly."

They've done this once before, using tracheal tissue from a seal. Sawatzki and Puryear have long studied live seals along the North Atlantic coast for influenza and distemper viruses, and they make an annual trip to the Gulf of Maine to gather samples from gray and harbor seals. Puryear says they confirmed that seal cells could be infected by SARS-CoV-2 and could replicate the virus, which means that seals may support this viral infection. The new funding will allow them to establish additional cell lines to confirm or deny whether other species are susceptible to the virus.

"Part of the drive for this is to try to remove as much bias as possible in case there are animal populations that are being understudied," says Puryear. "Maybe an animal is asymptomatic, but the species could be a silent reservoir that's going completely unstudied. Nature is vast. So we're going to sample and study pretty much whatever comes through the door."

Provided by Tufts University