Experts are warning pet owners about a potentially fatal dog parasite recently discovered in the portion of the Colorado River that runs through Southern California.
Scientists from the University of California (UC), Riverside confirm the presence of the flatworm Heterobilharzia americana, or liver fluke, in a portion of the river. According to the statement posted on the UC Riverside website, this is the first reported recording of the parasite in this location. It was only previously seen “almost exclusively” in Texas and other Gulf Coast states and was “never been reported this far west.”
The flatworm can lead to canine schistosomiasis, affecting the liver and intestines. The symptoms can take several months to fully manifest in an infected animal.
“Dogs can die from this infection, so we are hoping to raise public awareness that it’s there,” says Adler Dillman, professor of parasitology and nematology at UC Riverside. “If you’re swimming in the Colorado River with them, your pets are in peril.”
The discovery follows a research effort led by Prof. Dillman after reports of infection in local dogs started in 2019. Since then, 11 dogs in three California counties have been confirmed with this disease, and one has died. All infected dogs were reported to have spent time at the Colorado River in the town of Blythe in Riverside County.
Dillman and his research team went to the riverbanks to collect more than 2,000 snails, which is known to transmit the flatworm.
“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,” says Dillman. “Not only was it a surprise to find H. americana, we also did not know that the snails were present here.”
After its development within a snail, the flatworm seeks out a mammal for infection, surviving independently for approximately 24 hours. Dogs or raccoons become infected if they are in the water or drinking during this period.
“It gets into the veins of the intestinal lining, and that’s where it develops into an adult and mates,” says Dillman. “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. The immune system tries to deal with it, and hard clusters of immune cells called granulomas form. Eventually the organ tissues stop functioning.”
“Treatment typically involves use of multiple medications and close monitoring of the dog by a veterinarian,” says Emily Beeler, DVM, MPH, of the Veterinary Public Health Program of the Los Angeles County Department of Public Health.
Dr. Beeler says the symptoms can manifest in dogs gradually, starting with loss of appetite, vomiting, diarrhea, then “profound weight loss and signs of liver disease.”
For more information, visit the UC Riverside website.