Flatworm Parasite (Heterobilharzia) in Dogs

Cecilia de Cardenas
Oct 06, 2008
3 min read
Image: Photo Grapher / via Image Bank

Heterobilharzia americanum Infection in Dogs

Heterobilharzia americanum is a waterborne flatworm trematode parasite that typically infects raccoons and dogs. The parasite follows a cycle that begins with sexual reproduction in the intestine, where the eggs are laid so that they can be carried out of the infected animal by way of the fecal discharge. Once the egg has left the body, it hatches in water, finds a host snail, and moves into its miracidia stage, where it reproduces itself asexually into multiple spores – the sac-like larval form. The sporocysts, as they are called, multiply in turn, again asexually, to become cercariae, the next larval stage of the heterobilharzia americanum flatworm.

It is in this stage that the larvae leave the snail to search for a warm-blooded host. The cercariae latch onto a host animal and burrow through the skin, infecting the body systemically. The cercaiae then travel to the lungs, and then to the veins of the abdominal organs. There, they mature into male and female flukes (flatworms), and begin the next cycle of sexual reproduction. Most eggs are carried to the intestinal wall, where they erode their way into the intestines to be passed in the feces, but often there will be some eggs that travel through the bloodstream to the liver and other organs, causing disease.

Symptoms and Types

  • Itching and irritation of the skin
  • Diarrhea (possibly bloody)
  • Vomiting
  • Weight loss
  • Mild anemia
  • Increased protein in the blood
  • Increased calcium in the blood


This parasite is most common in swamps and bayous, but cases of heterobilharzia americanum infection have been reported in waters from Texas, Florida, Louisiana, and North Carolina. The parasite is most active in the morning hours, but it has a 24-hour life span, outside of a host body, so it is possible to be infected at any time of the day in water that has this parasite. Snail populations are at their highest during the summer months, and because this parasite uses snails as an intermediary host, it is during the summer months that the risk of infection is at its height as well.

Dogs that spend time in water that harbors the heterobilharzia americanum parasite are at risk for infection. The only way to avoid infection is to avoid water that is known to be infected, or could possibly be infected.


You will need to give a thorough history of your dog's health, onset of symptoms, and recent activities, such as whether your dog has been swimming recently. A complete blood profile will be conducted, but the most definitive way to find the parasite is by taking a stool sample and examining it microscopically.

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