In the waters surrounding Cape Cod, a curious phenomenon has captured the attention of scientists: while harbor seals often fall ill and sometimes die from influenza, gray seals appear to remain unaffected. This intriguing difference in disease response has prompted researchers to delve deeper into the immune systems of these marine mammals.
The investigation is led by Milton Levin, Ph.D., an associate research professor of pathobiology and veterinary science at the University of Connecticut (UConn). Levin and his team are exploring whether cytokines, small proteins that play a crucial role in immune responses, could be the key to understanding this disparity.
Investigating the Immune Response
Both gray seals and harbor seals are known to contract influenza, yet the clinical outcomes differ significantly between the two species. Levin’s research focuses on cytokines, which are produced by immune cells and help coordinate the body’s defense mechanisms. “They help initiate an immune response and then they help tamp down the immune response once a threat is gone,” Levin explains.
Surprisingly, when Levin’s team analyzed the cytokine profiles from blood samples of over 100 gray seal pups, they found no discernible difference between those that had contracted influenza and those that hadn’t. This unexpected result was published in the Journal of Wildlife Diseases, suggesting that gray seals might not mount a detectable immune response to the virus at all.
“Right now, it seems that the seals are not responding at all to influenza, and that’s probably why we’re not seeing clinical signs and why they don’t die,” Levin says.
Understanding Marine Mammal Immunity
The findings challenge existing research on other animals, where infected individuals typically show distinct cytokine profiles. Levin posits that the lack of response in gray seals could be a protective mechanism, preventing the damaging effects of an overactive immune response, known as a “cytokine storm.” In humans, such storms can cause more harm than the pathogens themselves.
“If we can understand why gray seals don’t generate that response, that could tell us more about the immune response in general in marine mammals versus other species,” Levin notes. This could have broader implications for understanding how marine mammals interact with pathogens and potentially inform human medicine.
Challenges and Future Directions
The next phase of research involves examining cytokine responses in harbor seals. However, logistical challenges abound. Unlike gray seals, which separate from their mothers early and are accessible to researchers, harbor seals remain with their mothers for several weeks, making sample collection more difficult.
Levin’s decade-long research aims to unravel how viruses circulate among marine populations and what factors influence susceptibility to disease. “We’re trying to understand how pathogens, viruses, and influenza in particular, are being passed between species and if it is being transmitted to humans or are humans transmitting it to seals,” Levin says.
Collaborative Efforts and Broader Implications
This research is a collaborative effort involving UConn, Tufts University Cummings School of Veterinary Medicine, the University of Maine, and the National Oceanic and Atmospheric Administration Northeast Fisheries Science Center. Christina McCosker from the University of Maine serves as the lead author of the study.
The work aligns with CAHNR’s Strategic Vision area focused on Fostering Sustainable Landscapes at the Urban-Rural Interface. It underscores the importance of understanding marine ecosystems and their health, which has far-reaching implications for biodiversity and environmental sustainability.
As scientists continue to explore the mysteries of gray seals’ flu resistance, the findings could pave the way for new insights into immune responses across species, potentially offering clues for managing diseases in both wildlife and humans.
