Rare carnivorous parasite kills four otters and can spread to humans

A rare carnivorous parasite has killed four otters in California for the first time, with scientists warning the disease could spread to humans.

The otters all suffered from what scientists called the worst lesions on their bodies they’d seen in more than two and a half decades of research.

They had all contracted a previously unknown strain of toxoplasma gondii, a parasitic infection linked to miscarriage, seizures and encephalitis in humans.

They now fear the parasite lurks in oysters, clams, mussels and crabs and could infect humans if they are undercooked.

It is particularly dangerous because, unlike most other diseases, it can cross the blood-brain barrier and cause infection.

The four sea otters were each infected with a previously unknown strain of the parasite toxoplasma gondii.  They all had the worst lesions on their bodies scientists had seen (stock image)

The four sea otters were each infected with a previously unknown strain of the parasite toxoplasma gondii. They all had the worst lesions on their bodies scientists had seen (stock image)

Dr. Karen Shaprio, a pathologist at the University of California, Davis, sounded the alarm about the new threat.

“Because this parasite can infect humans and other animals, we want others to know about our findings, recognize cases quickly and, if they come into contact with it, take precautions to avoid infection,” she said.

“We report our preliminary findings to warn others about this concerning condition.

“Since toxoplasma can infect any warm-blooded animal, it can also potentially cause disease in animals and humans that share the same environment or food sources.”

The four sea otters were found stranded between February 2020 and March 2022.

Three of the four were females living within six miles of each other in San Luis Obispo County, between San Francisco and Los Angeles, while the other was an immature male in Santa Cruz County, just outside the Bay Area.

Genetic testing revealed they were infected with a previously undetected version of toxoplasmosis called COUG.

Little is known about this variant, but it appears to cause more serious disease than other types.

In addition to the lesions, all animals also had steatitis, or severe inflammation of their body fat.

It was the first time the disease had been identified in marine animals in California.

It was not clear how they became infected, but scientists said it was probably caused by the parasite being washed into the sea by heavy rainfall.

Toxoplasma parasites are normally found in cat feces. But heavy rains can wash the parasites into fresh or salt water.

The scientists said that because sea otters live near coasts, they are therefore vulnerable to infection with the parasite.

Toxoplasmosis, the disease it causes, is common in otters. But this rare type has not been spotted before.

The parasite can infect humans, with more than 800,000 Americans contracting the disease each year.

The Centers for Disease Control and Prevention (CDC) also says it causes hundreds of deaths and thousands of hospitalizations.

It is usually picked up from eating contaminated food, such as undercooked shellfish, or through close contact with domestic cats that harbor the parasite.

In most cases, the parasitic infection causes no symptoms.

But in the past it has been linked to serious symptoms, including miscarriages and seizures.

It is unclear whether people who contract this strain are more likely to develop serious illness.

Dr. Shapiro added that the newly diagnosed strain in California came as a “complete surprise.”

“The COUG genotype has never before been described in sea otters, either anywhere in the California coastal environment or in any other aquatic mammal or bird,” she said.

The warning was in the magazine Frontiers in marine science.


Toxoplasmosis is caused by a common brain parasite Toxoplasma gondii.

It is usually contracted through cat feces, but can also be caught from uncooked infected meat, especially lamb or pork.

The condition is often symptomless, but it can cause miscarriage or stillbirth in pregnant women and can also be dangerous for people with weakened immune systems.

Up to half of the world’s population is thought to be infected with toxoplasmosis, but without showing any symptoms.

The infection can be detected using a blood test.

It usually requires no treatment, but medication can be used in more vulnerable patients.