Why do 4 dead California sea otters have scientists so alarmed?

This spring, wildlife officials in California did something unusually dramatic: They sounded a public alarm about the deaths of four wild sea otters infected with an extremely rare parasite.

the tension of toxoplasma gondii, The single-celled parasite that causes the disease toxoplasmosis, never before reported in the US, is unusually virulent and could pose a threat to other mammals, including people.

The otters, found dead off the central California coast between 2020 and 2022, had “astronomically high levels of parasites and massive amounts in the blubber, which was severely inflamed,” says Melissa Miller, a wildlife veterinarian with the Department of Fish and California Wildlife. . That’s a striking contrast to other types of toxoplasmosis, which typically affect an animal’s brain and central nervous system.

“These otters looked sicker and died faster than otters infected with other strains. We’re talking weeks instead of months or years,” says Miller, co-author of a new study published in Frontiers in Marine Sciences. (Learn how this common parasite manipulates the minds of its hosts.)

Infect at least one third of the world’s human population at any given time, Toxoplasma it can only reproduce in the intestine of domestic or feral cats, so pregnant women are warned not to clean cat litter boxes. Although usually mild, the parasite is widespread in nature, affecting all warm-blooded mammals; 60 percent of adult southern sea otters have active infections, Miller says. The southern sea otter, a subspecies, is endangered in California with only 300 animals left.

“These findings completely surprised us,” says Karen Shapiro, an associate professor at the University of California, Davis, School of Veterinary Medicine.

“We have been characterizing other types of toxoplasmosis in sea otters for 20 years, but this was utter nonsense – a strain linked to a really serious form of disease that we had never seen before. We needed people to know that,” says Shapiro, also a co-author of the study.

Genetic analysis revealed another surprise: The strain of the parasite matched samples taken from two Canadian pumas nearly 30 years ago. That strain, named COUG for its origin, was detected and identified after residents of Victoria, British Columbia, contracted toxoplasmosis from contaminated drinking water.

People can also be exposed through their cats or through some foods, such as undercooked meat and raw shellfish. Symptoms, if any, include mild fever and muscle aches, but some people, especially those who are immunocompromised, can develop serious illness, with damage to the brain and other organs. (Read how toxoplasmosis can affect the human brain.)

At least five additional suspected cases of COUG in otters are currently in various stages of testing, Shapiro adds.

“The more cases we find and the more we learn, the more we need to figure out how to protect animals and people.”

cheating parasite

After Toxoplasma Entering the ocean through stormwater runoff, the parasite is picked up and concentrated by shellfish and crabs, which are favorite foods of southern sea otters. Researchers recently linked another group of T. gondii variants known as type X with cats from nearby hydrographic basins, cementing the land-sea connection.

T. gondii it can survive in seawater for up to two years. The parasite can also lie dormant for years, hiding in cells and then reactivating if the host’s immune system weakens.

“They are considered one of the most successful parasites globally because they have so many tricks up their sleeves to move around and hide on hosts,” says Miller.

And they may be getting a boost from increased precipitation in the west.

California’s recent heavy rains, flooding and high tides, which are expected to intensify due to climate change, could increase the amount of Toxoplasma-Infected cat fecal matter flowing into the ocean. However, Shapiro cautions that more long-term studies are needed to draw any solid conclusions. (Read how heavier rainfall will increase water pollution.)

To connect the dots, scientists are studying a host of different parasites and the pathways by which they make their way through the environment. Shapiro’s research has found more Toxoplasma in mussels collected during the wet season than during the dry season, while another study linked increased levels of the parasite in the ocean with increased rainfall.

another fatal disease

Scientists have confirmed a land-sea-rain connection with another parasite, Sarcocystis neuroma, which receives less attention because it is not a human pathogen. Housed in opossums rather than cats, sarcus, as it’s called, is easier to track down because the disease develops more quickly. In one such event, 40 sea otters died on a 12-mile stretch of coastline. (Read how toxoplasmosis is hurting endangered seals in Hawaii.)

“We see a pretty close trend where typically if a big storm hits, several weeks later we have an increase in sarco cases,” says Devinn Marie Sinnott, a veterinary pathologist and Ph.D. UC Davis student who is studying the phenomenon.

Sinnott spent the rainy winter last worrying about the arrival of each new storm. “Part of me knew we needed the rain, but part of me is scared because I know we’re going to see a lot of sick otters soon. It’s a bit heartbreaking.”

The biggest photograph

In the meantime, the researchers hope that the public’s love for sea otters and other marine life will focus attention on the ways that land use and development are affecting the marine environment.

“We are not only responsible for climate change, but also for the ways in which we have altered coastal environments so that there is much more pollution in the sea,” says Shapiro.

“The fact that we have filled in all these wetlands and paved all these parking lots and driveways means that the water has nowhere to go but downstream, and the water is entering the sea with much more force, taking with it the parasites. .”

Plus, sea otters have nowhere else to go, Sinnott says. The range of the southern sea otter is limited by increasing populations of great white sharks in the north and south. (Read how some sea otters are recovering in western North America.)

“Sea otters are already under a lot of pressure from habitat loss, contact with oil spills, shark bites and other diseases, and their population is still trying to recover from its record low,” Sinnott says.

“If we want to preserve and conserve this keystone species, we really need to consider this land-sea connection and how climate change is affecting the health of its population.”