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Davis, California

Wednesday, February 28, 2024

Recent sea otter deaths linked to a rare strain of parasitic infection

A parasitic strain of Toxoplasma gondii called the COUG strain has killed four California sea otters


By KATIE HELLMAN — science@theaggie.org 

A recent news release reported that four California sea otters have died from a severe form of toxoplasmosis, an infection that comes from the microscopic parasite Toxoplasma gondii. The initial research is published in the journal Frontiers in Marine Science.

“Our findings reveal a novel and concerning lesion pattern for southern sea otters with systemic toxoplasmosis that appears to be associated with an atypical T. gondii strain described in an aquatic animal for the first time,” the study reads. 

Although the particular strain of infection is rare, the parasite is relatively common, and sea otters are particularly vulnerable to infection due to their habitat’s location near the shoreline. Sea otters may consume marine invertebrates that expose them to the infection or come into contact with the parasite’s eggs through rainwater runoff. 

The strain of Toxoplasma was found through DNA testing to be one known as COUG, which was first identified in 1995. These findings raise concern about the strain’s potential to infect more sea otters and possibly other warm-blooded animals, including humans.

Devinn Sinnott of the UC Davis School of Veterinary Medicine co-authored the study and addressed this concern.

Toxoplasma gondii in general can affect any warm-blooded species, so humans are susceptible as well as many domestic and wild animals,” Sinnott said. “This particular strain has never been reported in humans, but that’s not to say that it couldn’t potentially infect humans.”

All four sea otters in the study were found to have steatitis, an inflammation of body fat, which was detected through microscopic analysis of the otters’ tissues. 

Melissa Miller of the California Department of Fish and Wildlife, who co-authored the study, commented on the virulence of the strain.

“We have seen that certain genetic strains of Toxoplasma in otters appear to be a little bit more pathogenic than others,” Miller said. “What’s astounding about the COUG strain is that it appears to be capable of killing adult otters that don’t have obvious pre-existing health conditions. I’ve been looking at otters for 25 years and I haven’t seen that before.”

This is the first time that the COUG genotype has been found in sea otters or anywhere along the California coast.

“Sea otters are a threatened species and they are already under a lot of pressure from different sources, including other diseases, toxins, their habitat and food limitations,” Sinnott said. “Finding this new strain that’s killing animals very rapidly is particularly concerning from a conservation standpoint.”

Scientists noted that the presentation of the parasitic infection in the otters exhibited unusual characteristics. For example, although large quantities of the parasites were identified throughout the otters’ bodies, none were discovered in their brains. In the case of deadly toxoplasmosis, the central nervous system is usually heavily affected.

“As a wildlife pathologist, I’m all about pattern recognition,” Miller said. “If you listen to [sea otters] and let them teach you about what’s happening in the environment, they’ll do it and they’ll do an extremely good job. They’re one of the finest environmental sentinels I’ve ever worked with in my career.”

Written by: Katie Hellman — science@theaggie.org