Sea otters killed by lethal strain of Toxoplasma 

An unusual parasite strain that has killed at least four sea otters may pose a threat to marine animals and humans, according to a study from the California Department of Fish and Wildlife and UC Davis. The experts report that the animals died from an unusually severe form of toxoplasmosis, a disease caused by the microscopic parasite Toxoplasma gondii.

The researchers noted that toxoplasmosis is common in sea otters, but the new Toxoplasma strain appears to be more lethal and capable of rapidly killing healthy adult otters.

The scientists warn that this rare form of toxoplasma infection, which has never been seen on the California coast before, could threaten both wildlife and humans if it contaminates the environment and the marine food chain.

“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,” said study co-author Melissa Miller. “We encourage others to take extra precautions if they observe inflamed systemic fat deposits in sea otters or other marine wildlife.”

Toxoplasma gondii is a common parasite that infects most species of warm-blooded animals and causes toxoplasmosis. The sea otters that were found stranded with the new strain of Toxoplasma had severe inflammation of their body fat – a condition called steatitis. According to the researchers, this is a very unusual finding in sea otters with toxoplasmosis.

“The appearance of this lethal type of Toxoplasma in coastal California is concerning for two main reasons: First, because of potential population health impacts on a threatened species, and second, because this parasite could also affect the health of other animals that are susceptible to Toxoplasma infection,” said study co-author Devinn Sinnott of the UC Davis School of Veterinary Medicine.

Through microscopic examination, the experts found that the deceased otters had high numbers of Toxoplasma parasites in their tissues. However, the parasites were not present in the brain, which is usually affected in sea otters with fatal toxoplasmosis.

DNA tests revealed that the animals had been infected with a rare strain of Toxoplasma called COUG, which was first identified in 1995 in Canadian mountain lions.

“This was a complete surprise,” said study senior author Karen Shapiro of the UC Davis School of Veterinary Medicine. “The COUG genotype has never before been described in sea otters, nor anywhere in the California coastal environment or in any other aquatic mammal or bird.”

“I have studied Toxoplasma infections in sea otters for 25 years, and I have never seen such severe lesions or high parasite numbers,” said Miller. “We are reporting our preliminary findings to alert others about this concerning condition. 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.”

According to Sinnott, larger-scale studies are needed to understand the potential impact of infection by the COUG Toxoplasma strain on sea otter populations, how geographically dispersed it is, how it is being introduced into the ocean, and what other animals might be affected.

The study is published in the journal Frontiers in Marine Science.

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By Chrissy Sexton, Earth.com Editor

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