Flukes, Lung

CDC Yellow Book 2024

Travel-Associated Infections & Diseases

Author(s): Susan Montgomery

INFECTIOUS AGENT: Paragonimus spp.



The Americas

East Asia (China, Japan, Korea)

Southeast Asia


Adventurous eaters


Practice safe food precautions

Avoid raw or undercooked freshwater crab or crawfish


A clinical laboratory certified in moderate complexity testing; or contact CDC’s Parasitic Diseases Branch (404-718-4745; parasites@cdc.gov)
Parasitological diagnosis: DPDx

Infectious Agent

Paragonimiasis is caused by helminth parasites in the genus Paragonimus, especially Paragonimus westermani.


Lung fluke infections are transmitted by eating raw or undercooked, pickled, or salted freshwater crab or crawfish 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 ≥15 species of Paragonimus, which vary by geographic area and definitive host. Paragonimus species are found in western Africa, the Americas, and Asia. P. westermani, the most common cause of human disease, occurs predominantly in eastern and southern Asia.

Clinical Presentation

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 like tuberculosis, with shortness of breath, cough, and hemoptysis. Extrapulmonary infections can occur and cause serious disease when the central nervous system is involved. Infections are usually associated with eosinophilia, especially during the larval migration stage.


Refer travelers to an infectious disease specialist if there is clinical suspicion of a lung fluke infection. 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.

Clinicians can obtain diagnostic assistance and confirmatory testing from the Centers for Disease Control and Prevention (CDC)’s Division of Parasitic Diseases and Malaria DPDx laboratory (dpdx@cdc.gov), and from the Parasitic Diseases Hotline for Healthcare Providers (404-718-4745; parasites@cdc.gov).


Treatment is with praziquantel; triclabendazole is an alternative.


Travelers should avoid eating raw or undercooked freshwater crab or crawfish.

CDC website: www.cdc.gov/parasites/paragonimus/

The following authors contributed to the previous version of this chapter: Kristina M. Angelo

Fischer PU, Weil GJ. North American paragonimiasis: epidemiology and diagnostic strategies. Exp Rev Anti-Infect Ther. 2015;13(6):779–86.

World Health Organization. Foodborne parasitic infections: Paragonimiasis (Lung fluke). Available from: www.who.int/publications/i/item/WHO-UCN-NTD-VVE-2021.5

Xia Y, Ju Y, Chen J, You C. Hemorrhagic stroke and cerebral paragonimiasis. Stroke. 2014;45(11):3420–2.