Sea otters dying from rare parasite that could spread to humans: study

By Stephen Beech via SWNS

Sea otters are dying from a rare parasite strain that could spread to other species - including humans, warns new research.

The deadly form of toxoplasma infection poses a major threat to marine and other animals, say scientists.

Four sea otters that washed up on the West coast of the United States died from an unusually severe form of toxoplasmosis, according to a report by the California Department of Fish and Wildlife and the University of California, Davis.

Scientists say that the disease is caused by the microscopic parasite Toxoplasma gondii.

They warned that the rare strain, never previously reported in aquatic animals, could pose a health threat to other marine wildlife and humans.

The preliminary findings, published in the journal Frontiers in Marine Science, note that toxoplasmosis is common in sea otters and can be fatal.

Scientists say the unusual strain appears to be "especially virulent" and capable of rapidly killing healthy adult otters.

The rare strain of Toxoplasma hasn’t been detected on the California coast before.

Scientists are concerned that if it contaminates the environment and the marine food chain, it could pose a public health risk.

At present, no infections with the strain have been reported in humans.

But corresponding author Dr. Melissa Miller, of the California Department of Fish and Wildlife, said: “Because this parasite can infect humans and other animals, we want others to be aware of our findings, quickly recognize cases if they encounter them and take precautions to prevent infection.

“We encourage others to take extra precautions if they observe inflamed systemic fat deposits in sea otters or other marine wildlife.”

She said Toxoplasma gondii is a common parasite hosted by wild and domestic cats and shed in their droppings.

Although healthy humans rarely experience symptoms, toxoplasmosis can cause miscarriages and neurological disease.

Miller said sea otters are especially vulnerable to Toxoplasma infection because they live near the shoreline where they may be exposed to the parasite’s eggs in rainwater runoff, and they eat marine invertebrates that can concentrate the parasites.

The four sea otters described in the study stranded between 2020 and 2022. All had severe inflammation of their body fat - a condition known as steatitis. Severe steatitis is a very unusual finding in sea otters with toxoplasmosis.

Study co-author Devinn Sinnott, of UC Davis School of Veterinary Medicine, said: “The appearance of this lethal type of Toxoplasma in coastal California is concerning for two main reasons.

"First, because of potential population health impacts on a threatened species, and second, because this parasite could also affect the health of other animals that are susceptible to Toxoplasma infection."

Microscopic analysis of tissues confirmed Toxoplasma as the cause of death for all four otters.

Large numbers of the parasites were observed throughout each body except the brain, which is typically one of the major organs affected in sea otters with fatal toxoplasmosis.

DNA testing identified a rare strain of Toxoplasma called COUG in all four cases.

The strain was first found in 1995 in Canadian mountain lions during surveillance after a nearby outbreak among humans, but the strain of Toxoplasma responsible for the outbreak was never reported.

Scientists say that the detection of COUG in sea otters is "concerning" for the health and recovery of the threatened species.

Study senior author Professor Karen Shapiro, of UC Davis School of Veterinary Medicine,said: “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.”

She said all four otters stranded during periods of high coastal rainfall, which means they may have been exposed to Toxoplasma eggs via storm runoff.

Although three of the otters stranded near each other, it is unclear whether they were all infected in the same location.

How the unusual strain might affect humans or other animals remains unknown.

Miller said: “I have studied Toxoplasma infections in sea otters for 25 years, and I have never seen such severe lesions or high parasite numbers.

“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, including mussels, clams, oysters, and crabs that are consumed raw or undercooked.”

The research team said that increased surveillance could lead to the COUG strain being identified in other species.

Sinnott added: “We still have much to learn.

“Larger-scale studies are needed to understand the potential impact of infection by the COUG Toxoplasma strain on sea otter populations, how geographically dispersed it is, how it is being introduced into the ocean and what other animals might be affected.”