A Parasite That Can Be Deadly for Dogs Has Been Found in California

West Coast dog parents, take note: A parasite that is potentially deadly for dogs has been found in California. Since 2018, ten dogs have gotten sick and one has died from a disease linked to the parasite Heterobilharzia americana, commonly known as “liver fluke.” This week, researchers finally discovered the presence of the parasite — which typically lives in Texas and the South — in Colorado River in California.

What is H. americana?

The liver fluke is a parasite “endemic to the Gulf Coast and South Atlantic region of North America,” wrote lead author Anil Baniya in a new report published in Pathogens. But in recent years, researchers have found the liver fluke in new states across the country, including Indiana, Tennessee, and Utah. The parasite is transmitted by snails, and it can infect dogs as well as wildlife like raccoons, bobcats, and rabbits. Once it infects dogs, the parasite reaches the intestines and releases thousands of eggs, causing a variety of dangerous reactions in the pup’s organs. “Veterinarians consistently emphasize that H. americana is frequently overlooked in diagnoses and is becoming a growing concern,” wrote Baniya. 

Between 2018 and 2023, 11 cases of schistosomiasis — the disease caused by the liver fluke — were reported in three Southern California counties. Five of the dogs showed symptoms including vomiting, weight loss, and diarrhea, according to a report by the LA County Department of Health. One of the dogs tragically passed away. 

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“Travel history of the infected dogs indicated that before their diagnosis, all 11 dogs had been in the Colorado River,” wrote Baniya. Based on these findings, researchers decided to collect over 2,000 snails from the banks of the river. They were able to determine that this is where the dogs likely contracted schistosomiasis. 

Adler R. Dillman, an expert on parasitology, was part of the team that discovered the presence of the flatworm. “I was super excited to finally provide an answer as to what was happening with those dogs,” Dillman told the LA Times. “We suspected it was this parasite, but once we finally confirmed it, I was jumping up and down with excitement.”

What should pet parents look out for?

Symptoms of schistosomiasis include vomiting, diarrhea, weight loss, increased thirst, and yellowish eyes. “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 for the Los Angeles County Department of Public Heath, told the LA Times. 

The disease can’t be spread between dogs and humans or from dogs to other dogs — so unless your pup has direct contact with freshwater sources, there is little cause for concern. Humans can “develop a self-limiting rash after contact with contaminated water sources,” Sara Strongin, chief veterinarian at Riverside County Department of Animal Services, said in a report.  

The parasite can be detected through fecal exams or liver biopsies. If it’s found early, it can be treated with antiparasitic drugs. According to Strongin, the best prevention is to keep dogs away from freshwater sources like rivers and lakes — and they definitely shouldn’t wade in the Colorado River any time soon.