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Flatworm Parasite (Heterobilharzia) in Dogs

What Is Heterobilharzia, or the Flatworm Parasite in Dogs?

Heterobilharzia americana is a flatworm parasite commonly found in freshwater bodies like ponds, lakes, swamps, and canals, particularly prevalent in southern states such as Texas, Louisiana, Florida, Mississippi, Alabama, Georgia, and South Carolina, but cases have been reported as far north as Kansas. This parasite utilizes freshwater snails as intermediate hosts, where it undergoes initial development before infecting other animals. The infection is restricted to areas where these snails are abundant. Once matured, the flatworms are released from the snails into the water, seeking hosts like dogs or other mammals for further infection.

Flatworms enter a dog’s body by penetrating the skin and migrating to the lungs, potentially causing symptoms like coughing. From the lungs, they move through the bloodstream to the liver, where they reach maturity and begin reproducing. In the liver, male and female flatworms reproduce, and the eggs can penetrate the intestinal wall, eventually being expelled in the animal’s feces. The life cycle continues if the eggs hatch in water and encounter another freshwater snail host to initiate infection.

Symptoms and Types

The symptoms stemming from flatworm infestation in dogs are often nonspecific and can be mistaken for other ailments. When the flatworms penetrate a dog’s skin, they may induce a rash-like reaction, particularly noticeable in dogs with short hair or where the skin lacks coverage, such as the stomach area. If you and your dog swim or wade in infested waters, you might also experience a rash known as swimmer’s itch.

As the flatworms migrate to different areas of the dog’s body, additional symptoms may manifest. Migration to the lungs can lead to symptoms like coughing, loss of appetite, and lethargy. The eggs produced by adult flatworms invade the intestinal tract, causing diarrhea, which may be bloody or contain mucus, along with fever and reduced appetite. Other symptoms may include drooling, dehydration, increased thirst, and in severe cases, collapse.

Without treatment, Heterobilharzia americana can prove fatal. The intensity of symptoms depends on the number of mature flatworms present in the dog, the locations of worm penetration, and the extent of inflammation. Some research indicates that this process may extend up to 84 days.


The source of flatworm infection in dogs is the parasite Heterobilharzia americana. This particular flatworm parasite employs freshwater snails as its intermediate host, a crucial stage before it can successfully infect a warm-blooded mammal. Importantly, dogs cannot contract the infection by ingesting eggs from the feces of an infected dog. The flatworms depend on the intermediate host, the snail, for the eggs to undergo further development. It’s essential to note that the eggs themselves pose no harm to dogs, and humans cannot become infected through contact with the stool of an infected dog.


Flatworm infection is often challenging to diagnose due to its symptoms resembling those of other diseases, contributing to undiagnosed cases and, in severe instances, death or euthanasia due to diminished quality of life.

When a veterinarian suspects flatworm infection, they typically perform a direct saline preparation using your dog’s fresh stool to confirm the diagnosis. Unlike most other parasites, flatworm eggs do not float, making them difficult to detect through routine stool examinations.

In some cases, an abdominal ultrasound may be conducted to detect any changes in the liver, spleen, abdominal lymph nodes, and intestinal walls, although these changes may not directly lead to a diagnosis but can aid in assessing the extent of damage.

Veterinarians may also utilize clinical tests like ELISA and PCR assays, specifically designed to diagnose flatworm infections. The decision to run these tests often depends on the information provided by the owner, including the dog’s clinical signs and recent exposure to freshwater in regions where flatworms are prevalent.


To treat flatworm infection in dogs, veterinarians typically administer high doses of deworming medication aimed at eliminating the parasite. Medications like praziquantel or fenbendazole are commonly used and can be effective if the infection is detected early. During the treatment process, your dog may need to be hospitalized for monitoring.

When diagnosed promptly, dogs have a chance of successful treatment. However, in many cases, the infection leads to irreversible damage, and euthanasia may be recommended to alleviate the suffering of the dog.

Recovering from Flatworms

When flatworm infection is diagnosed early and treatment is effective, dogs can experience swift recovery without enduring long-term adverse effects. Even if the infection is detected later but responds well to treatment, a dog’s life can still be saved, although chronic gastrointestinal issues and other complications may persist.

The crucial factor for successful treatment lies in early identification. It’s imperative to provide your veterinarian with a comprehensive history, including details about the geographical area and whether your dog has been exposed to freshwater, to aid in accurate diagnosis and treatment planning.

Flatworm Parasite (Heterobilharzia) in Dogs FAQs

Can flatworms be fatal to dogs?

Yes, if not identified early in the disease’s progression, flatworm infection can often be fatal.

Are flatworms harmful to dogs?

Yes, flatworms pose a significant risk to dogs, causing severe and debilitating diseases that can result in death if not treated promptly.

Can humans contract flatworms from dogs?

No, humans cannot contract flatworm infections directly from their dogs.

How do dogs acquire flatworms?

Dogs contract flatworms by swimming in freshwater sources where infected freshwater snails reside.

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