Sea otters swim together in the Pacific Ocean. A deadly, newly detected strain of the parasite Toxoplasma gondii is threatening sea otters, and potentially other species. Credit: Laird Henkel, CDFW
Key points:
- Four stranded sea otters in California were killed due to a rare but deadly parasite.
- At present, no infections with the strain have been reported in humans living in the area, but it can infect all warm-blooded species.
- Though it rarely affects healthy humans, Toxoplasmosis has been linked to possible miscarriages and neurological diseases.
Four sea otters that stranded in California died from an unusually severe form of toxoplasmosis, according to a study from the California Department of Fish and Wildlife and the University of California, Davis. The disease is caused by the rare, microscopic parasite Toxoplasma gondii, which researchers say they’ve never previously seen in aquatic animals.
The preliminary findings, published in Frontiers in Marine Science, note that while toxoplasmosis is common in sea otters and can be fatal, this unusual strain is capable of quickly killing healthy adult otters. California has never had the rare strain of Toxoplasma detected on its coasts. Scientists are concerned that a possible contamination of the environment and the marine food chain might pose a public health risk.
At present, no infections of this strain have been reported in humans.
“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 corresponding author Melissa Miller of the California Department of Fish and Wildlife. “We encourage others to take extra precautions if they observe inflamed systemic fat deposits in sea otters or other marine wildlife.”
Toxoplasma gondii is commonly hosted by wild and domestic cats and shed through their feces. Toxoplasmosis has been linked to possible miscarriages and neurological diseases, but it rarely affects healthy humans.
The four sea otters described in this study, stranded between 2020 and 2022, all had severe inflammation of their body fat—a condition called steatitis. Severe steatitis is a very unusual finding in sea otters with toxoplasmosis. Additionally, high numbers of the parasites were observed throughout each body except the brain, which is typically one of the major organs affected in sea otters with fatal toxoplasmosis.
All four otters stranded during periods of high coastal rainfall, which means they may have been exposed to Toxoplasma eggs via storm runoff. Although three of the otters stranded near each other, it is unclear whether they were all infected in the same location.
The specific strain of Toxoplasma, called COUG, was first found in 1995 in Canadian mountain lions during surveillance after a nearby outbreak among humans, but the strain of Toxoplasma responsible for the outbreak was never reported.
“I have studied Toxoplasma infections in sea otters for 25 years, and I have never seen such severe lesions or high parasite numbers,” Miller said. “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.”