APR 12, 2023 6:00 AM PDT

Unusual Parasite Found in Cat Poop is Killing Sea Otters

WRITTEN BY: Mandy Woods

Four southern sea otters observed stranded off the coast of California near Santa Cruz and San Luis Obispo between February 2020 and March 2022 were diagnosed with fatal protozoal steatitis and systemic toxoplasmosis. This is the first discovery of this specific parasitic strain in an aquatic species that has been shared via food sources, indicating potential future health risks to both humans and animals. 

The University of California Davis and the California Department of Fish and Wildlife carried out performed necropsies, histopathology, and immunohistochemistry analyses, to confirm the presence of the parasite. The parasite in question? A microscopic organism identified as Toxoplasma gondii. 

The parasite itself is not unfamiliar to otters; however, this particular strain is causing concerns due to its virulence and the rapid pace at which it spreads. It is also the first time this particular strain has appeared off the coast of California, and contamination of the surrounding environment is a pressing matter for environmental scientists. Toxoplasmosis in humans can cause neurological disease and miscarriage in pregnant people. This is why pregnant people are often deterred from cleaning kitty litter.  

Otters are currently protected as keystone species, meaning their role in the environment tremendously impacts other species. Considered top predators, they maintain kelp forests, estuaries, and embayments by preventing the overpopulation of sea urchins, which feed on the kelp forests that provide food and shelter for many other marine species. Maintaining kelp forests also helps reduce levels of atmospheric carbon dioxide, which can absorb and sequester within kelp. 

Toxoplasma gondii enters the ocean through wastewater outfalls and stormwater via fecal matter from wild, feral, and ordinary house cats. The parasite then accumulates within filter feeder species such as snails and mussels, and even crabs, clams, and oysters, favorite otter food sources. Toxoplasma gondii can virtually infect all warm-blooded animals, with reproduction and sexual development occurring only in the intestines of Felidae members. Eventually, the parasites are shed in feline feces. 

This particular strain was first diagnosed in Canadian mountain lions in 1995 while treating a breakout among nearby humans; however, no previous cases in aquatic or bird species were recorded in California, and the strain of the nearby outbreak was never reported. It is believed the four otters were stranded during high rainfall, potentially exposing them to the toxic Toxoplasma eggs via stormwater.

Chemicals in indoor litter do not prevent the spread of this parasite. The concern is the uncertainty about how the parasite would affect humans in sharing similar favorite food sources when undercooked. Larger scale studies are needed to understand the potential impacts infections of this strain could have on otter populations and the transference to human and other animal populations, as well as its geographic dispersal. 

Sources: Science Direct,  Frontiers, EurekAlert, CDC , Defenders of Wildlife, Science

About the Author
Bachelor's (BA/BS/Other)
Mandy (She/Her) is a Scientific Writer and an active Field Archaeologist. She has worked in the Southwest, Midwest, and Great Basin for Historical Archaeology and Resource Management. She received her B.A. from the University of New Mexico with a focus in Archaeology and History. In her free time, she is outdoors with her two dogs, Nala and Nova. She channels her passion for nature and exploration into her career.
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