Four sea otters in California died from toxoplasmosis through a rare strain of the Toxoplasma gondii parasite, and researchers warn that the strain could pose a threat to humans.

The unusual strain of Toxoplasma gondii that was studied had not been detected in California before. The findings of a study, which was conducted by scientists at California Department of Fish and Wildlife and University of California, Davis, was published in the Frontiers in Marine Science journal this week.

The four sea otters in the study were stranded on the California coast between 2020 and 2022. The study said that the toxoplasmosis cases were particularly bad, with high numbers of parasites being found all over the otters' bodies except for their brains.

Researchers are concerned about the strain contaminating the marine ecosystem, which would pose a public health risk.

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Group of sea otters

Otters floating at the surface, resting in Monterey Bay, California. (Francois Gohier/VW Pics/Universal Images Group via Getty Images)

UC Davis researchers say that the strain has not been reported in humans yet, but wanted to warn the public about their findings.

"Because this parasite can infect humans and other animals, we want others to be aware of our findings, quickly recognize cases if they encounter them and take precautions to prevent infection," Melissa Miller of the California Department of Fish and Wildlife said. 

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Sea otter laying on its back

Sea Otter frolicking in the kelp bed, in the no otter zone south of Point Conception, off the Santa Barbara County coast.  (Ricardo Dearatanha/Los Angeles Times via Getty Images)

"Since Toxoplasma can infect any warm-blooded animal, it could also potentially cause disease in animals and humans that share the same environment or food resources, including mussels, clams, oysters, and crabs that are consumed raw or undercooked," Miller added.

Miller also said that, after studying Toxoplasma infections in sea otters for 25 years, she had never observed such high parasite numbers or severe lesions.

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Sea otters in water

Sea otters gather at Elkhorn Slough in Moss Landing, Calif. on Thursday, April 12, 2018. (Paul Chinn/The San Francisco Chronicle via Getty Images)

According to the CDC, over 40 million Americans carry the Toxoplasma parasite, but their immune systems usually prevent the parasite from causing illness or any adverse symptoms. 

The CDC recommends cooking meat to sufficient internal temperatures and rinsing produce to avoid catching the parasite.