Unusual strain of parasite kills 4 California sea otters

Four sea otters that washed up in California died of an unusually severe form of toxoplasmosis, according to a study by the California Department of Fish and Wildlife and the University of California, Davis (UC Davis). The disease is caused by the microscopic parasite Toxoplasma gondiia rare strain of Toxoplasma which has not been previously detected on the California coast.

The preliminary results, published in the journal Marine Science Frontiers, note that toxoplasmosis, which is likely a recent arrival on the California coast, is common in sea otters and can be fatal. This unusual strain appears to be particularly virulent and capable of rapidly killing healthy adult otters. Currently, no infections with the strain have been reported in humans, according to a UC Davis press release.

“Because this parasite can infect humans and other animals, we want others to know about our findings, quickly recognize cases if they encounter them, and take precautions to prevent infection,” said Melissa. Miller of the California Department of Fish and Wildlife, and correspondent. author of the report on the findings, in the press release. “We encourage others to take extra precaution if they observe inflamed systemic fat deposits in sea otters or other marine animals.”

Common parasite, rare outcome

T. gondii is a common parasite harbored by feral and domestic cats and excreted in their feces. Although healthy humans rarely show symptoms, toxoplasmosis can cause miscarriages and neurological diseases. Sea otters are particularly vulnerable to Toxoplasma because they live close to shore where they can be exposed to parasite eggs in runoff and they eat marine invertebrates which can concentrate parasites.

The 4 sea otters described in the reported study were stranded between 2020 and 2022. All suffered from soapstone, a condition characterized by severe inflammation of body fat. According to the investigators, severe soapstone is a very unusual finding in sea otters with toxoplasmosis.

“The appearance of this deadly type of Toxoplasma in the California coast is of concern for 2 main reasons: first, because of the potential impacts on the health of the population of an endangered species, and second, because this parasite could also affect the health of other animals likely to Toxoplasma infection,” Devinn Sinnott of the UC Davis School of Veterinary Medicine, co-author of the study, said in the statement.

Confirmed microscopic examination of tissues Toxoplasma as the cause of death for the 4 otters. High numbers of parasites were observed in every body except the brain, which is usually one of the main organs affected in sea otters with fatal toxoplasmosis.

DNA tests have identified a rare strain of Toxoplasma called COUG in all 4 cases. This strain was first discovered in 1995 in Canadian cougars during surveillance after a nearby human outbreak, but the strain of Toxoplasma responsible for the outbreak was never reported. The detection of COUG in sea otters came as a surprise, according to Karen Shapiro of the UC Davis School of Veterinary Medicine, lead author of the study. “The COUG genotype has never been described before in sea otters, or anywhere in the coastal environment of California, or in any other mammal or aquatic bird,” Shapiro said in the statement.

Sea otters under threat

All 4 otters stranded during periods of heavy coastal rainfall, meaning they may have been exposed to Toxoplasma eggs via storm runoff. Although 3 of these otters stranded near each other, it is not known if they were all infected in the same place. How this unusual strain might affect humans or other animals is also unknown.

“I’ve studied Toxoplasma infections in sea otters for 25 years, and I have never seen such severe lesions or such high parasite counts,” Miller added. “We are reporting our preliminary findings to alert others to this concerning condition. From Toxoplasma can infect any warm-blooded animal, it could also cause disease in animals and humans that share the same environment or food resources, including mussels, clams, oysters and crabs that are eaten raw or undercooked.

Investigators noted that with increased surveillance, the COUG strain could be identified in other animals. “We still have a lot to learn,” Sinnott said. “Larger scale studies are needed to understand the potential impact of infection with COUG Toxoplasma pressure on sea otter populations, their geographic dispersal, their introduction into the ocean, and other animals that may be affected.

Reference

Sea otters killed by an unusual parasite strain. Press release. UC Davis. March 23, 2023. Accessed March 24, 2023. https://www.ucdavis.edu/health/news/sea-otters-killed-unusual-parasite-strain