Scientists have discovered for the first time in Southern California dog-killing worms that have infected at least 11 pets, one of which died.
A team from the University of California Riverside (UCR) discovered that Heterobilharzia Americana, a flatworm commonly known as the liver fluke, is being transmitted by snails living along the Colorado River bed.
The worms can cause canine schistosomiasis, a disease that affects the liver and intestines of dogs and was previously only found in Texas, Louisiana and Florida.
The findings have suggested that the tiny flatworms could be spreading throughout the Colorado River and the smaller rivers that flow into it, providing a broader spread than previously known.
A team from the University of California Riverside (UCR) discovered that snails along the Colorado River bed transmitted Heterobilharzia Americana, a flatworm commonly known as liver fluke.
UCR nematology professor Adler Dillman said, “Dogs can die from this infection, so we hope to raise public awareness of its existence.”
“If you’re swimming in the Colorado River with them, your pets are in danger.”
Los Angeles County Public Health issued an advisory in 2023 confirming 11 cases of canine schistosomiasis spanning from 2018 to 2023.
Dillman and his team learned of the local infections and headed to a region of the river where the 11 dogs spent time swimming.
The team collected more than 2,000 snails and found two species that harbored flatworms: Galba cubensis and Galba humilis.
“Not only was it a surprise to find H. Americana, but we also didn’t know snails were present here,” Dillman said.
This discovery was made at Mulberry Grove Pond, which receives water from Mill Creek, one of the tributaries of the Colorado River.
After transforming into one of the snails, the worm ventures out in search of a mammal to infect. At this stage, it can only survive on its own for about 24 hours. If a dog or raccoon is in water or drinking, it becomes infected.
Galba cubensis was previously believed to be the worm’s only natural host, with G. humilis showing only marginal susceptibility.
Both snails come mainly from America, but have invaded Asia, Europe and Africa.
“This discovery was made in Mulberry Grove Pond, which receives water from Mill Creek, one of the tributaries of the Colorado River,” the researchers shared in the study.
“This pond is approximately 280 feet from Mill Creek and the shore of the Colorado River is approximately 2.17 miles away from the pond.”
The team, however, believes that the parasite could be spreading throughout the Colorado River and taking advantage of the rivers that flow into it to find new hosts.
“In-depth studies are needed to investigate the extent of parasite infestation along the banks of the Colorado River and its tributaries in the United States and Mexico to obtain a clear understanding of parasite infection,” the study reads.
The team collected more than 2,000 snails and found two species that harbored flatworms: Galba cubensis and Galba humilis.
After transforming into one of the snails, the worm ventures out in search of a mammal to infect.
At this stage, it can only survive on its own for about 24 hours. If a dog or raccoon is in water or drinking, it becomes infected.
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“It enters the veins of the intestinal lining and that’s where it develops into an adult and mates,” Dillman said.
‘The presence of adults in the veins is not the problem. It is the eggs that reach the lungs, spleen, liver and heart. The immune system tries to deal with this and tough clumps of immune cells called granulomas form. Eventually, the organ tissues stop functioning.’
Once infected, it can take several months before the worst symptoms of the disease appear.
Emily Beeler, a veterinarian with the Los Angeles County Department of Public Health, said: “Symptoms begin gradually with loss of appetite and eventually include vomiting, diarrhea, profound weight loss and signs of liver disease.
“If your dog develops these symptoms after swimming in the Colorado River, it is a good precaution to ask your veterinarian for a simple fecal test.”
“Treatment typically involves the use of multiple medications and close monitoring of the dog by a veterinarian,” Beeler said.
The researchers emphasized that H. Americana is not known to be capable of causing disease in humans.
‘It can cause swimmer’s itch, a red rash when it penetrates human skin. But it’s not capable of causing infection,” Dillman said, while he noted that worms can easily leach out of water systems.