Dog-Killing Flatworm Parasite Spreads to Western US; Experts Warn Pet Owners of the Dangers of Liver Fluke

A type of parasite has been afflicting dogs in Texas and other Gulf Coast states, causing a debilitating and often fatal disease. The flatworm was believed to only exist in this region, but they have recently spread to the far West.

A Surprising Discovery

Experts at the University of California Riverside discovered the flatworm (Heterobilharzia americana), commonly known as liver fluke, in spots along the Colorado River running through Southern California. Before, it has never been seen outside of Texas and surrounding areas, though some studies also found infections in Kansas, North Carolina, and Louisiana.

The parasitic worm can cause canine schistosomiasis, an illness which affects the liver and intestines of dogs. There are available treatments for infected canines, but they are not always successful and can even lead to euthanasia.

Led by UCR nematology professor Adler Dillman, the research team examined the water samples from Riverside County after several cases of the parasitic infection were reported in local dogs. The infection is generally transmitted through snails, so the experts collected over 2,000 gastropods along the banks of the Colorado River. They also examined their DNA to identify the presence of the waterborne parasite.

Dillman and his colleagues were surprised to find two species of snail which carry the flatworm. It was not only strange to find the liver fluke, but they also did not know that the snails were present in the area.

Heterobilharzia americana works by first making its way into the snail's body, traveling through its system. Once it transforms, the parasite proceeds to find a mammal host to infect within 24 hours before it fails to survive further on its own. Dogs and raccoons are susceptible to acquiring one of these flatworms through fresh water, either from swimming in or drinking it.

A flatworm can enter into the veins of the animal's intestinal lining, where it will mature, breed, and lay eggs. The eggs then cause an autoimmune reaction as they transfer into the heart, liver, spleen, and lungs. The immune system responds by creating clusters of cells known as granulomas, eventually leading to organ tissue failure.

Symptoms of Dog Infections

It could take a few months before noticeable and serious symptoms appear after a parasitic infection. According to Emily Beeler, a veterinarian from Los Angeles County Department of Public Health, the symptoms of canine schistosomiasis occur gradually. Profound weight loss, diarrhea, vomiting, loss of appetite, and signs of liver disease are all symptoms linked with the progression of the disease.

Beeler warns pet owners that if their dogs have these symptoms after swimming in the Colorado River, it is a good precaution to ask their veterinarian for a simple fecal test. The treatment may involve use of multiple drugs and close monitoring of the dog.

The Heterobilharzia americana parasite cannot cause schistosomiasis infection in humans. However, it has already affected 11 dogs in three counties in California, killing one since 2019. Because of the recent discovery in western U.S., experts advise pet owners to be vigilant and aware of the water in which they take their dogs to swim. A lot of freshwater sources like swamps and rivers can sustain such parasites, even if humans have yet to identify them in those bodies of water.