Viral-caused cancer in California sea lions has major health implications for humans

Reviewed by Emily Henderson, B.Sc.Feb 3 2021

20-plus years of data in a newly released study by The Marine Mammal Center shows ocean pollutants is one of the leading causes of cancer in sea lions and highlights how exposure to environmental contaminants can fast-track the likelihood of humans developing virally caused cancers.

Scientists at The Marine Mammal Center - the world's largest marine mammal hospital - have found that viral-caused cancer in adult California sea lions is significantly increased by their exposure to toxins in the environment.

The study is the result of over 20 years of research and examination of nearly 400 California sea lion patients by The Marine Mammal Center.

The Marine Mammal Center has been at the forefront of researching and understanding cancer in California sea lions and its connection to both ocean and human health. Since cancer in sea lions was first discovered in 1979, between 18-23 percent of adult sea lions admitted to the Center's hospital have died of the fatal disease - the highest prevalence for a single type of cancer in any mammal, including humans.

The study, which was published in Frontiers in Marine Science, a peer-reviewed research journal, concluded that efforts to prevent ecosystem contamination with pollutants must improve in order to prevent virally caused cancer development in both wildlife and humans.

"This paper's conclusions mark a significant milestone in piecing together the complicated puzzle of cancer development in California sea lions," said Dr. Pádraig Duignan, Chief Pathologist at The Marine Mammal Center and co-author of the study. "The decades of research looking into this deadly disease clearly shows the ocean environment we all share is in trouble and that we need to find solutions to protect our collective health."

The findings also show that California sea lions have among the highest levels of certain persistent organic pollutants in the blubber of any marine mammals - a disturbing report that is cause for concern for scientists across the globe.

Even though some of the pollutants we're finding in the blubber have been out of use for years, these cancer-causing elements remain in the environment for a very long time and wreak havoc on opportunistic coastal feeders like sea lions."

Dr. Pádraig Duignan, Study Co-Author and Chief Pathologist, Marine Mammal Center

"It concerns me knowing that we consume very similar seafood as these cancer victims and that the ocean is raising a loud and clear alarm in the sick bodies of a sentinel species. We need to continue this critical research and collaborate with the human cancer doctors to find patterns to help discover the link between sea lions and ourselves."

Previously, researchers at The Marine Mammal Center determined that these sea lions are infected with a herpesvirus similar to one that causes Kaposi's sarcoma (viral cancer) in humans. In this newly released study, scientists used complex statistical analysis and modeling to investigate the relative roles of the various factors in the development of fatal metastatic cancer.

The results showed that the damage of the DNA in sea lions occurs due to a number of factors, including the interaction of many environmental factors, including chemical contaminants and pollutants; and infections by tumor-promoting viruses like Otarine herpesvirus-1.

Additionally, their findings found that the animals' own genetic predisposition was not a significant factor in developing cancer.

"While there is more to be learned about the complex factors that play into the development of this disease, what we learn from these animals contributes to research that underpins the threat to human health from pollutants in the ocean," said Dr. Frances M. D. Gulland, the lead author of the study who worked at The Marine Mammal Center for 25 years.