Rare flesh-eating parasite kills four otters and could spread to humans

A rare flesh-eating parasite has killed four otters in California for the first time, with scientists warning the disease could jump to humans.

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

Each had caught a previously unknown strain of toxoplasma gondii, a parasitic infection linked to miscarriage, seizures and brain inflammation in humans.

They now fear the parasite may be lurking in oysters, clams, mussels and crabs and could infect humans if these are undercooked.

It is particularly dangerous because, unlike most other diseases, it is capable of crossing the blood-brain barrier to cause infection.

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

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

‘Because this parasite can infect humans and other animals, we want others to be aware of our findings, quickly recognize cases and, if they encounter them, take precautions to prevent infection,’ she 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.’

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

Three of the four were females who lived within six miles of each other in San Luis Obispo county, which is 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 had been infected with a previously undetected version of toxoplasmosis, named COUG.

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

As well as the lesions, all the animals also had steatitis, or severe inflammation of their body fat.

It marked the first time the disease had been recorded in any sea animals in California. 

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

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

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

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

The parasite is able to infect humans, with more than 800,000 Americans catching the disease every year. 

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

It tends to be picked up from eating contaminated foods, such as undercooked shellfish, or from close contact with pet cats harboring the parasite.

In most cases, the parasitic infection causes no symptoms.

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

It is unclear whether people who catch this strain are more likely to suffer severe disease.

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, nor anywhere in the California coastal environment or in any other aquatic mammal or bird,’ she said. 

The warning was issued in the journal Frontiers in Marine Science.


Toxoplasmosis is caused by a common brain parasite Toxoplasma gondii.

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

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

Up to half 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 does not usually require treatment but medication can be used in more vulnerable patients.  

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