Runstadler Lab Investigates SARS-CoV-2 Transmission to Wildlife and Marine Mammals

As in humans, the implications of spillover infections and newly circulating virus can potentially be highly impactful, so documenting these responses is evidence of at least exposure, providing impetus to continue monitoring and consider what management steps might be important, especially for at-risk populations and the implications for potential spillback to humans.

– Dr. Jonathan Runstadler

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus that causes COVID-19, has been detected in more than 60 animal species—though until now, had not been closely studied in New England wildlife and in marine mammals. The Runstadler Lab at Cummings School of Veterinary Medicine at Tufts University conducted two research projects to address these knowledge gaps, notably finding evidence consistent with a possible human-to-deer spillover event and the first serological evidence of SARS-CoV-2 exposure in marine mammals in the United States.

The studies were featured in the July 2026 issues of Viruses and PLOS ONE, respectively titled, “SARS-CoV-2 Surveillance in Free-Ranging Wildlife in New England and Virginia, United States, 2022-2025” and “Serological evidence of SARS-CoV-2 exposure in marine mammals in the United States between 2020 and 2025.”

The concurrent studies were led by Idrissa Nonmon Sanogo, Ph.D., postdoctoral research scholar in comparative virology and zoonotic diseases at Cummings School, in the laboratory of Dr. Jonathan Runstadler, professor and chair of the Department of Infectious Disease and Global Health and Agnes Varis Professor in Science and Society.

The Runstadler Lab studies infectious disease spread with particular focus on influenza in wildlife species. Funded by the U.S. Department of Agriculture (USDA), the two SARS-CoV-2 studies relied on robust collaborations with Tufts Wildlife Clinic and organizations across the country that the lab has established for its wildlife research. Sanogo greatly expanded this network for the SARS-CoV-2 projects.

“Idrissa came to the lab with a background working on influenza that fit perfectly with the project funding to look at SARS-CoV-2 in wildlife,” says Runstadler. “He served as project lead for the entire study. He’s become an integral part of our group.”

Sanogo sent partner organizations—including state fish and wildlife departments, wildlife clinics, animal rehabilitation centers, marine conservation organizations, and aquariums—kits for collecting swab and serum samples and standard operating protocols on collecting the samples. The Runstadler Lab tested the samples for active SARS-CoV-2 infection and serological evidence of previous exposure, sharing the results with the partner organizations.

“What I find fascinating about this work is really the collaboration with other people. This network has been amazing for us to be successful with this project,” says Sanogo.

The first study investigated whether the SARS-CoV-2 virus was spilling over into the wildlife of New England. Samples from 1,646 animals across 29 wildlife species were collected between 2022 and 2025 from partnering wildlife clinics, animal rehabilitation facilities, and state fish and wildlife agencies in New England and Virginia, and then tested and analyzed by the Runstadler Lab.

“My goal was to see how the virus is being transmitted between humans and animals, if the virus can adapt to animals, and to develop experimental models that we can use to assess susceptibility,” says Sanogo. “We do swab and serological testing because with viral infection you have a short window to detect the virus, maybe one or two weeks after. Antibodies can persist longer, so we have a clear, longer view to see if the species we are sampling were exposed to the virus at some point.”

The team found active infection in three white-tailed deer. Sequences from the deer were closely related to contemporaneous human SARS-CoV-2 sequences from the same region, consistent with a possible human-to-deer spillover event.

“The result on the positive deer samples was curious,” says Runstadler. “On the one hand, overall sampling is too sparse for definitive conclusions about the origin of those viruses. On the other hand, transmission from human to deer is consistent with other results across the U.S. and elevates concern about the maintenance and potential further evolution of those viruses in wildlife.”

The lab also found serological evidence (past exposure) of SARS-CoV-2 in nine animals from three species: Eastern cottontail rabbit, Eastern coyote, and raccoon.

“It is surprising to see the positive serology as evidence of infection in some of these species like the rabbit, since we do not yet understand exactly how those animals are being infected or exposed,” says Runstadler.

Sanogo notes that there was no widespread exposure of SARS-CoV-2 among the wildlife of New England. “This was the first objective, to see if the virus has been transmitted to those animals and if it is evolving and being transmitted back to humans. We should continue doing surveillance in those animals to be able to detect SARS-CoV-2 and other emerging pathogens that could pose a risk of spillback to humans.”

Similar to the wildlife study, Sanogo built upon the lab’s network of marine mammal organizations from previous research projects on influenza exposure, spread, and spillover. He expanded this network further with the SARS-CoV-2 study, collaborating with 25 marine conservation organizations and aquariums across the east and west coasts, Hawaii, and Alaska.

Spillover risk of SARS-CoV-2 for marine mammals derives from transmission through direct contact with humans (such as at rehabilitation centers), with the potential to spread among their species. Additionally, SARS-CoV-2 genome fragments (though not infectious) have been detected in untreated wastewater and marine environments, raising questions about whether environmental contamination could create opportunities for exposure of marine mammals in coastal areas.

The Runstadler Lab tested samples from 1,017 live and deceased stranded animals representing 21 marine mammal species from 2020 to 2025. The team found no active infections of SARS-CoV-2, but did find antibodies in three species of marine mammals: harbor seal, California sea lion, and grey seal—the first time SARS-CoV-2 exposure has been detected in marine mammals in the United States.

“As in humans, the implications of spillover infections and newly circulating virus can potentially be highly impactful, so documenting these responses is evidence of at least exposure, providing impetus to continue monitoring and consider what management steps might be important, especially for at-risk populations and the implications for potential spillback to humans,” says Runstadler.

Sanogo adds, “Some of those species are highly social, especially the sea lion; they can be grouped thousands of animals together. This was also our concern because of the widespread exposure in the human population—if this happened in animals, it might decimate the population.”

Sanogo developed cell culture models of several wildlife species to investigate their susceptibility to SARS-CoV-2. He is currently refining those models for studies of other respiratory viruses.