118 - Trematodes

Abstract

Heterobilharzia americana Infection (Heterobilharziasis/Canine Schistosomiasis)•Cause: Heterobilharzia americana (Platyhelminthes, Trematoda, Digenea, Strigeidida, Schistosomatidoidea, Schistosomatidae).•First Described: Heterobilharzia americana was first described as an adult worm recovered from a bobcat (Lynx rufus) in 1929, and more fully described in specimens from a raccoon (Procyon lotor) in 1943. The parasite was first reported in dogs in Louisiana in 1961.•Affected Hosts: A variety of wildlife hosts, most commonly the raccoon (P. lotor). Dogs are the most frequently identified domestic animal hosts, but the parasite has also been shown to cause disease in horses and llama.•Intermediate hosts: Freshwater snails in the lymnaeid family, with Fossaria cubensis, Lymnae cubensis, and Pseudosuccinia columella confirmed as intermediate hosts by experimental infection.•Geographic Distribution: Primarily the southeastern United States, but the range appears to be expanding.•Route of Transmission: Penetration of intact skin by the larval cercarial stage that is released from snails in fresh water.•Major Clinical Signs: Many infections are subclinical, but the most frequent signs are chronic or recurrent diarrhea, weight loss, and sometimes hematochezia in response to adult parasites in the mesenteric veins and migrating eggs in the intestinal mucosa. Hepatic fibrosis and pancreatitis can occur due to inflammatory changes associated with hematogenously disseminated eggs in various tissues.•Differential Diagnoses: Depending on signs, these are a wide variety of neoplastic, toxic, or infectious/inflammatory causes. In a case series review, possible differentials included cholecalciferol toxicity, ethylene glycol toxicity, lymphoma, and pancreatitis. A variety of infectious pathogens can cause enteritis and hemorrhagic diarrhea. The differential diagnosis for hypercalcemia (sometimes present) includes malignancy-associated disease, endocrinopathies, renal failure, or a variety of infectious or inflammatory diseases.•Human Health Significance: No human infections with H. americana have been reported. However, it is possible that the free-swimming cercarial stage may be able to penetrate human skin causing “cercarial dermatitis” as reported from the closely related avian schistosomes found in waterfowl.