A mysterious cancer that’s been wiping out sea lions for years is likely caused by toxic chemicals and herpes, researchers in California have found.
Scientists have for two decades studied one type of aggressive cancer that has killed almost 25 percent of the sea lions brought to the Marine Mammal Center in Sausalito, the Los Angeles Times reported.
The disease is believed to be among the highest prevalence of a single type of cancer in any mammal, including humans, the outlet reported.
When researchers first detected the cancer, sea lions were being exposed in the ocean to barrels of industrial trash, radioactive materials, oil refinery waste, rotting meats and various acid sludges, the paper reported.
“Sea lions, they’re coming up on the beach, using the same waters that we swim and surf in, eating a lot of the same seafood that we eat,” said Frances Gulland, a University of California, Davis researcher serving on the US Marine Mammal Commission.
“They’re predisposed to cancer by these high levels of legacy compounds that are still in the environment — and we are also exposed to these chemicals.”
Gulland and other researchers studied the cancer in 394 sea lions, ruling out inbreeding and other possible causes.
The team found a previously unknown herpes virus was linked to the cancer, the report said.
The marine animals were more likely to become sick with the cancer when their blubber contained higher concentrations of chemicals including DDT, a pesticide that poisoned birds and fish, and PCBs, a banned substance that had been used in electrical and hydraulic equipment, paints, plastics and rubber products, according to the report.
“It is extraordinary, the level of pollutants in these animals in California. It is a big factor in why we’re seeing this level of cancer,” said study co-author Padraig Duignan, who is chief pathologist at the Marine Mammal Center.