Scientists in California are raising the alarm after four sea otters were killed by an unusual strain of a common parasite spread by cats, a concerning but preliminary finding that researchers told Forbes signals a potential health threat to other animals prone to infection, including humans.
Toxoplasma gondii is a near-ubiquitous parasite that infects a wide variety of warm-blooded animals, including humans, and is transmitted by wild and domestic cats.
While it commonly infects sea otters, genetic testing revealed all four had been infected with a particularly unusual strain of the parasite that appears to be capable of rapidly killing its host, according to a study published Wednesday in Frontiers in Marine Science.
All infected otters—three were found in San Luis Obispo County and one in Santa Cruz County—housed high numbers of parasites and showed an unusual pattern of severe parasite-linked damage to stores of body fat, as well as damage to many other tissues, said study author Melissa Miller of the California Department of Fish and Wildlife.
Miller told Forbes the rare parasite strain has only been detected in wild animals three times before, twice in Canadian mountain lions in 1995 and again years later in a feral pig in California’s Sierra Nevada Mountains.
The strain’s discovery in California’s coastal waters is concerning for the state’s sea otters—recognized as a threatened species—the researchers said, as well as a potential hazard to humans, domestic animals and other wildlife, all of whom are vulnerable to Toxoplasma infection.
Though the strain has not been identified in any other animals, the researchers said it poses a possible threat to public health as humans can ingest Toxoplasma from contaminated sea water or seafood.
What We Don’t Know
It’s not clear whether the parasite is a new arrival to the California coast, or if researchers discovered something that has been there for a while and was not noticed, Miller told Forbes. Available evidence suggests the strain is new—over 25 years of otter necropsies haven’t revealed similar patterns of parasite-associated fat damage and previous surveys of otters and other animals did not detect the parasite—but Miller said scientists still can’t rule out the possibility it “was simply missed in prior monitoring efforts.”
What To Watch For
Miller told Forbes a number of other potential cases of parasite-associated fat damage have been identified in sea otters. The samples are “awaiting further testing and confirmation,” and Miller said the careful process “takes time.”
Researchers are monitoring the environment carefully to try and catch any sign of the unusual parasite strain. Karen Shapiro of the UC Davis School of Veterinary Medicine, the study’s senior author, told Forbes not DNA matching the strain has been found in seawater or shellfish during monitoring efforts. However, “finding samples with sufficient quality and quantity of DNA” to study thoroughly “is really hard,” Shapiro said. “I would not be surprised if we are missing it.”
Toxoplasma is a ubiquitous parasite. It is “very good at spreading itself around in the environment and exploiting new habitats and new hosts,” Miller told Forbes, adding that “it is considered one of the most globally successful parasites for this reason.” It passes into aquatic ecosystems in water runoff and is often concentrated in marine invertebrates like shellfish. Around 11% of people in the U.S. ages six years and older have been infected with Toxoplasma, the CDC estimates, a figure that rises as high as 60% in some parts of the world. Human infections can persist for a long time, possibly for life, but most are kept in check by the immune system and the majority are completely unaware of their infection. Symptoms vary and can range from flu-like symptoms to severe damage to the eyes, brain and other organs and, in some instances, death. Unborn children are particularly vulnerable and infection can trigger premature birth and a number of health issues. Cats are a vital part of the parasite’s life cycle and it’s shed in their feces (which is why pregnant people are advised against changing litter trays). Infections are also reported to change hosts; behavior—infected rats are attracted to cat urine—and in humans infections are linked to higher rates of suicide, rage, traffic accidents and schizophrenia.
What’s Killing California’s Sea Otters? House Cats (NYT)
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