Senior News Writer
sea otters floating on ocean surface

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The Inertia

Four dead sea otters that washed up on a small stretch of California coastline between 2020 and 2022 showed severe parasitic infections that could find their way into humans.

That’s the concern from California wildlife officials and researchers at the University of California, Davis, who published a study on the findings in the journal Frontiers in Marine Science on March 22.

The study found the four otters were all suffering from a special strain of toxoplasma gondii. Scientists had never observed the strain in aquatic animals before. But its toxicity to humans emerged in a previous outbreak in British Columbia. Researchers eventually traced that waterborne epidemic back to mountain lions.

T. gondii is prevalent in wild and domestic cat feces, researchers said. The unusual strain, called COUG, appears to be “highly virulent” in the cases of the recent transmission among otters.

Three of the infected otters washed up within 16 miles of each other, the researchers found. And all four deaths coincided with “periods of increased rainfall-driven surface water runoff.”

The paper’s authors warned that there’s a “high potential” the strain could spread to humans through food sources we share with marine animals.

“Due to high zoonotic potential and the risk of infection via shared marine food resources, these findings may also indicate potential health threats for other animals and humans,” the article said.

Infection in humans can cause fatal neurological disease, especially for anyone in an immunosuppressed condition. Miscarriage and congenital toxoplasmosis (or the infection of an unborn infant) are also possible.

According to the paper, the parasite can spread through a wide range of ocean mammal hosts, from sea cows to whales. The affected otters all showed severely inflamed fat deposits, but since no other confirmed cases exist in marine animals, symptoms in other species are relatively unknown.

Since scientists did link the heavy rainfall and resulting runoff to the virulent strain, the finding “underscores the need for detailed studies of T. gondii transmission at the land-sea interface,” the paper concluded.


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