Lung Fluke Infection

Infection with lung flukes in the genus Paragonimus (paragonimiasis) is a foodborne zoonosis. There are over 30 species of Paragonimus which are highly evolved parasites with a complex life cycle that involves at least three different hosts, such as snails, crustaceans, and mammals. Humans get Paragonimus lung flukes when they ingest raw crayfishes or crabs infected with fluke eggs or larva. The incubation period may vary from 1 to 2 months or even longer. In Asia, nearly 20 million people are infected with Paragonimus species. The parasite from the human gut passes through several organs and tissues to reach the lungs. Adult worms live in the lungs and the eggs are passed in the sputum or feces. The migrating worms in the pleural cavity produce pneumonia that is initially manifested as coughing up rusty brown or blood-stained sputum, chest pain, fever, chest tightness, difficulty in breathing, or bronchopneumonia.2

Paragonimus kellicotti is North American lung fluke, a species of flatworms in the genus Paragonimus. This parasite is well known to veterinarians and animal biologists in North America. The adult forms of P. kellicotti species reside and mate in the lungs of a variety of mammalian hosts, including dogs, cats, skunks, red foxes, coyotes, mink, bobcats, and humans, mainly in the midwestern and southern United States within the Mississippi River Basin. Most cases of paragonimiasis infection in the United States are transmitted by the ingestion of raw or undercooked crayfish, the preferred crustacean intermediate hosts for Paragonimus kellicotti. In some areas of North America 44% of crayfish are harbor lung fluke cysts.

The disease in dogs is characterized by a productive cough which produces frothy white material with numerous streaks of blood. Some infected dogs may have no signs, yet in heavy infestation, severe difficulty breathing followed by death may occur due to asphyxiation.3 The diagnosis of Paragonimus kellicotti may be made by the identification of the eggs in the bronchial mucus or in feces. Multiple fecal specimens might be required in suspected cases because the eggs are not always present. Fenbendazole is used to treat dogs with paragonimiasis. Treatment may have to be repeated in some cases and the prognosis is good.4

Crayfish are the preferred second intermediate crustacean hosts for Paragonimus kellicotti
Reprinted from NCTC Image Library


  1. North American Paragonimiasis (Caused by Paragonimus kellicotti) in the Context of Global Paragonimiasis
  2. Parasitic Pneumonia and Lung Involvement
  3. Paragonimiasis in a dog
  4. Small Animal Internal Medicine. Richard W. Nelson, C. Guillermo Couto