Lung fluke infections are transmitted by eating raw, partially cooked, pickled, or salted crab or crawfish that are infected with the immature form of the parasite. Ingested larval stages of the parasite are released when the infected crustacean is digested and then migrates from the intestines to other parts of the body. Most end up in the lungs, where they develop into adults and produce eggs. Human infections can persist for 20 years.
Human disease is caused by at least 15 species of Paragonimus, which vary by geographic area and definitive host. Paragonimus species are found in the Americas, western Africa, and Asia. Paragonimus westermani, the most common cause of human disease, occurs predominantly in eastern and southern Asia.
Patients with Paragonimus infection can present with an acute syndrome within 2 days to 2 weeks after ingestion. Infections of longer duration can present with signs and symptoms similar to tuberculosis, with cough, shortness of breath, and hemoptysis. Extrapulmonary infections may occur and cause serious disease when there is central nervous system involvement. Infections are usually associated with eosinophilia, especially during the larval migration stage.
DIAGNOSIS AND TREATMENT
If there is clinical suspicion of a lung fluke infection, travelers should be referred to an infectious disease specialist. Diagnosis is usually made by identifying eggs in stool or sputum. Serologic testing for P. westermani–specific antibodies can be helpful, especially for diagnosis of extrapulmonary infection; depending on the serologic assay, this testing can detect infections with other Paragonimus species because of differing levels of cross-reactivity among species. Treatment is with praziquantel. Clinicians can consult CDC to obtain more information about diagnosis and treatment (CDC Parasitic Diseases Inquiries: 404-718-4745 or firstname.lastname@example.org).
Avoid eating raw or undercooked freshwater snails, crab, or crawfish.