New parasite strain that killed sea otters may pose a risk to humans

Four sea otters, stranded in California, died from an unusually severe form of toxoplasmosis, which, according to scientists, may pose a health threat to other marine wildlife and humans.
According to the team from the California Department of Fish and Wildlife (CDFW) and the University of California – Davis, the disease is caused by a rare strain of microscopic parasite Toxoplasma gondii, which has never previously been reported in aquatic animals.
While toxoplasmosis is common in sea otters and can be fatal, this unusual strain called COUG appears to be especially virulent and capable of rapidly killing healthy adult otters.
“This was a complete surprise,” said Karen Shapiro of the university’s School of Veterinary Medicine, in a statement.
“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,” Shapiro said.
The preliminary findings, published in the journal Frontiers in Marine Science, did not report any cases in humans, but stated that the strain could be a risk to people eating seafood or ingesting contaminated water.
“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,” said Melissa Miller of the CDFW.
Toxoplasma gondii is a common parasite hosted by wild and domestic cats and shed in their faeces.
Although healthy humans rarely experience symptoms, toxoplasmosis can cause miscarriages and neurological disease. Further, the four sea otters described in the study were stranded between 2020 and 2022 with severe inflammation of their body fat — a condition called steatitis which is a very unusual finding in sea otters with toxoplasmosis.
Microscopic examination of tissues showed high numbers of the parasites throughout each body except the brain, which is typically one of the major organs affected in sea otters with fatal toxoplasmosis.
Miller, who studied Toxoplasma infections in sea otters for 25 years, said she has “never seen such severe lesions or high parasite numbers”. The team called for increasing surveillance to identify the strain in other animals.
“Because this parasite can infect humans and other animals, we want others to be aware of our findings, quickly recognise cases if they encounter them and take precautions to prevent infection,” Miller said.