Author(s): Susan Montgomery

Infectious Agent

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

Transmission

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.

Epidemiology

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.

Diagnosis

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

Treatment is with praziquantel; triclabendazole is an alternative.

Prevention

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

CDC website: Paragonimus