Heterobilharzia Americanum

Heterobilharzia Americanum

Jamie R. Egelston

Heterobilharzia Americanum

Heterobilharzia americanum is a waterborne, flatworm parasite that has been known to infect dogs, raccoons, deer, bobcats, nutria and marsh rabbits (McKown). It is in the snail helminthes family of parasites, Lymnaeid Fossaria cubensis and Pseudosuccinea columella (Kemp).
Even though Heterobilharzia americanum is called the “blood fluke”, the signs of infestation are related to the intestinal system. It also causes skin lesions at the site where the parasite enters the body (Kemp). The disease caused by Heterobilharzia americanum is called heterobilharziasis, canine schistosomiasis, or water dermatitis. Heterobilharzia americanum is unusual among flukes in that there are separate male and female forms. A related parasite in humans causes a disease known as “swimmer's itch” or “clam-digger's itch” (Nash).

Heterobilharzia americanum is related to the important disease-causing flukes in man called “schistosomes”. These are common in Africa, South America, and the Far East. The egg of Heterobilharzia americanum is passed in the feces of the dog and hatches almost immediately in water. The immature form swims around until it finds a snail. The immature form enters the snail where it matures into an infective form. These forms leave their snail host and swim in search of a dog or raccoon. But, they only leave the snail early in the morning. These forms only have one day to find a host before they die (Nash).
Upon entering a host, the infective forms enter the veins in the skin and are carried to the heart and lungs. By several routes, they migrate to the veins of the intestine and liver where they mature. A bulkier male worm mates with the very slender and petite female. She then moves into smaller veins and lays her eggs and then leaves. The contractions of the vessels and intestine actually push the eggs through the wall of the vessel, the wall of the intestine, and...