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Dog-Killing Parasite Is Spreading in the U.S.—Watch for These Symptoms

Over 10 canines have contracted the disease in California alone.

Living near the river has its perks: sweeping vistas, gorgeous hiking trails, and endless opportunities for summer fun. But for our four-legged companions, splashing around in freshwater can lead to adverse health effects. A new paper published in the journal Pathogens is warning dog owners of a fast-spreading dog-killing flatworm that's infiltrating the Colorado River and has left one dog dead.

Commonly referred to as liver fluke, Heterobilharzia americana is a flatworm that's derived from snails and latches onto mammals, University of California, Riverside scientists, and authors of the study, explain in a new release.

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The parasite is known to cause canine schistosomiasis, a disease that attacks the liver and intestines of dogs. The illness typically presents itself through severe GI symptoms such as diarrhea, hematochezia, or vomiting, per Texas A&M University's Veterinary Medical Services and Biomedical Sciences department. A veterinarian may prescribe high doses of parasite medication, such as praziquantel or fenbendazole, for treatment.

Until recently, H. americana was only believed to be in freshwater surrounding Gulf Coast states like Texas and Louisiana. However, UCR scientists can now confirm that the deadly dog parasite exists in California's portion of the Colorado River, too.

Co-author and UCR nematology professor Adler Dillman and his team of researchers traveled to Blythe, California, a town located along the banks of the Colorado River, where several H. americana canine infections have been reported.

"We actually found two species of snails that can support H. americana in the river in Blythe, and we found both snails actively shedding this worm. Not only was it a surprise to find H. americana, we also did not know that the snails were present here," Dillman revealed, noting that his team sampled more than 2,000 snails.

However, for a dog to become infected, the parasite must enter a canine's body within 24 hours of exiting a snail, or else it dies. Drinking river water or simply swimming is enough for a dog to contract H. americana.

In the release, Dillman explained that H. americana wiggles its way into "the veins of the intestinal lining," where it adults and mates. However, the real risk of potentially life-threatening illness comes from the parasite's eggs.

"The presence of the adults in the veins isn't the problem. It's the eggs that get into the lungs, spleen, liver, and heart," he said. "The immune system tries to deal with it, and hard clusters of immune cells called granulomas form. Eventually the organ tissues stop functioning."

Unfortunately, it could be several months before a dog starts exhibiting symptoms.

"Symptoms start gradually with a loss of appetite, and eventually include vomiting, diarrhea, profound weight loss, and signs of liver disease," Emily Beeler, a veterinarian with the Los Angeles County Department of Public Health, told UCR. "If your dog has these symptoms after swimming in the Colorado River, it's a good precaution to ask your veterinarian for a simple fecal test."

The hazardous sickness comes on the heels of another highly contagious respiratory illness amongst dogs, which some are calling "strep zoo." If left untreated, the canine illness can develop into a weeks-long sickness and possibly even pneumonia. As of Nov. 2023, Oregon's Department of Agriculture had documented 200 cases of the disease.

As for H. americana, 11 dogs in California have contracted the disease since 2019. One canine has died. Animal experts and health officials want to spread awareness of the fast-spreading potentially fatal disease.

"Dogs can die from this infection, so we are hoping to raise public awareness that it's there," Dillman said. "If you're swimming in the Colorado River with them, your pets are in peril."

Emily Weaver
Emily is a NYC-based freelance entertainment and lifestyle writer — though, she’ll never pass up the opportunity to talk about women’s health and sports (she thrives during the Olympics). Read more
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