After several sea otters washed up dead along California’s shores, scientists dug into the mystery and uncovered an unlikely pair of culprits: a strange strain of a brain-controlling parasite and feline poop.
The four sea otters were found stranded between February 2020 and March 2022. It’s known that this species can be especially vulnerable to infections of Toxoplasma gondii, a single-celled parasite found throughout the world that commonly infects domestic cats. It also infects humans and is suspected to change their behavior (more on that later).
Strangely, this unlucky gang of sea otters was suffering from severe inflammation of their body fat, an unexpected symptom for sea otters with toxoplasmosis. Their bodies were also riddled with the parasite, yet their brain was left relatively untouched, which is unusual since the parasite typically infects the nervous system.
“I have studied Toxoplasma infections in sea otters for 25 years, and I have never seen such severe lesions or high parasite numbers,” Melissa Miller of the California Department of Fish and Wildlife said in a statement.
Investigating the four cases, scientists at UC Davis found the sea otters were infected with a rare strain of the parasite T. gondii that’s never been reported in aquatic animals before. Scientists call it COUG, as it was first found in Canadian mountain lions during surveillance after a nearby outbreak among humans in the mid-1990s. It’s since been identified in many other animals, and is particularly virulent in mice.
“This was a complete surprise. 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,” added senior author Karen Shapiro of the UC Davis School of Veterinary Medicine.
The presence of the unusual COUG strain raised a worrying question: how was the parasite making its way from the mountains into the bellies of coastal creatures?
The researchers published a study that reported the deaths all occurred during periods of high rainfall and increased water runoff. Perhaps, they speculate, infected feral cats have pooped on land and the parasite trickled down to the coastline, where it resided in snails and shellfish that are eaten by the sea otters.
The scientists also note that this previously unknown pathway could impact other animals that are susceptible to Toxoplasma infection – including us. After all, we also like to eat oysters, clams, and mussels, just like sea otters.
In the US, an estimated 11 percent of the human population has been infected with T. gondii, according to the CDC. In various other parts of the world, the infection rate might be upwards of 60 percent.
Infection in humans doesn’t generally produce physical symptoms unless the host is immunocompromised, in which case it can be deadly. However, it has been linked to a number of bizarre behavioral changes in people.
Research suggests some infected men with toxoplasmosis are more impulsive and that infected people are significantly more likely to be involved in a fatal car crash than those free of the parasite. It’s also been linked to schizophrenia, although some of the evidence is sketchy.
The sea otter study didn’t explore whether the new parasitic pals of sea otters might be making them more adventurous or impetuous, but it does appear that these infections could pose a risk to sea otters, which are already endangered.
The study was published in March 2023 in the journal Frontiers in Marine Science.