Potentially Deadly Threat to Pets Spreading Across the US, Researchers Warn

A general view of dogs at Coindre Hall on April 21, 2014 in Huntington, New York.

A potentially deadly parasite has been found for the first time in California’s Colorado River, according to a recent study from University of California researchers.

The parasite, called Heterobilharzia americana, is a flatworm known as a liver fluke. Previously it was found in Gulf states but has now spread west, researchers with the University of California at Riverside said this month.

“Dogs can die from this infection, so we are hoping to raise public awareness that it’s there,” UC Riverside nematology professor Adler Dillman told UC Riverside News. “If you’re swimming in the Colorado River with them, your pets are in peril.”

The parasite can cause an illness called canine schistosomiasis, which targets the liver and intestines of dogs. The infection is primarily spread by a snail that transmits the worm.

In three California counties, the researchers said, 11 dogs have been infected since 2019, one of which died.

Researchers collected about 2,000 snails near the Colorado River in Blythe, California, after they learned all the dogs that were infected with the flatworm had swam there. They found that two species of snails in the river hosted the parasite.

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“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,” Mr. Dillman said. “Not only was it a surprise to find H. americana, we also did not know that the snails were present here.”

The study, they also found, suggest there is a “wider distribution” of the flatworm than was previously known. Other studies have found that many infections occur in Texas and Louisiana, although some have occurred in other states.

“Our findings have implications for public health, veterinary medicine, and biodiversity conservation, contributing to developing effective control strategies to prevent the spread of this emerging infectious disease,” the researchers said in the study, published in the journal Pathogens.

“In our study, we successfully confirmed the presence of Heterobilharzia americana for the first time along the shores of the Colorado River, infecting two species of snails, Galba humilis and Galba cubensis,” the study authors also wrote. “This significant finding marks the westernmost record of this endemic North American schistosome in the U.S. The identification of the parasite in an area with a documented history of canine schistosomiasis emphasizes the persistence and potential expansion of this parasitic threat.”

Warnings

The flatworm is a blood parasite that lives in the veins and can induce liver inflammation during the mating process, say researchers with Texas A&M University. The parasite can “invade the skin or mucous membranes of the definitive host (dogs or wild mammals) and gain access to the bloodstream, migrate to the liver, mature, and migrate to the mesenteric vessels to complete the life cycle,” it says.

“Dogs and other animals are exposed to the parasite when wading or swimming in freshwater. The immature stage of the parasite penetrates through the skin and ends up in the veins in the intestine. There, the adult parasites release eggs many of which end up in the liver, spleen, or other organs and cause significant damage. Dogs can die from organ failure and other complications of the disease,” Mr. Dillman told Newsweek last week.

Researchers said it can take weeks or months for signs of the infection to show up in a dog. Symptoms of infected animals can include weight loss, hematochezia, melena, diarrhea, vomiting, and lethargy, they said.

“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,” Emily Beeler, a veterinarian with the Los Angeles County Department of Public Health, said in a UC California news release.

Last year, the county’s health department sent out a warning (pdf) that there have been reports in Orange, Los Angeles, and Riverside counties of parasitic dog infection, calling on veterinarians to be aware of the disease’s symptoms.