Paragonimiasis: Symptoms, Causes, and Treatment
Updated: 2 days ago
Medically reviewed by Dr. Baraa Alnahhal, MD · Last reviewed: September 2026
TL;DR: Paragonimiasis is a parasitic infection caused by flatworms of the genus Paragonimus, typically contracted by consuming raw or undercooked crab or crayfish. While it primarily affects the lungs, causing symptoms like chronic cough and chest pain, it can also spread to the brain and skin. The condition is often misdiagnosed as tuberculosis or lung cancer due to similar symptoms. Fortunately, it is highly curable with short courses of antiparasitic medication, provided it is diagnosed and treated early.
Quick Answer: What is Paragonimiasis?
Paragonimiasis is a parasitic infection caused by several species of Paragonimus flukes, a type of flatworm. Humans contract the disease by eating raw, undercooked, pickled, or salted crustaceans, such as crabs or crayfish, contaminated with larvae. Once ingested, the larvae migrate from the small intestine to the lungs, where they mature into adults. Symptoms often include a persistent cough, fever, and chest pain, which can be mistaken for other respiratory illnesses. Diagnosis involves identifying parasite eggs in sputum or stool, and treatment typically consists of a brief course of antiparasitic drugs like praziquantel or triclabendazole.
Understanding Paragonimiasis
Paragonimiasis is a significant health concern in areas where raw or partially cooked crustaceans are part of the local diet. While most common in Asia, Africa, and Latin America, cases are also reported in the United States and Canada.
How Infection Occurs
The infection begins when a person ingests cysts containing young fluke larvae. These cysts are found in:
Raw or undercooked crab or crayfish.
Pickled, salted, or "drunken" crab (marinated in wine).
Contaminated juices from these crustaceans.
Once in the small intestine, the larvae emerge and travel through the body to the lungs. The immune system reacts by forming hard pockets, or cysts, around the adult worms. These cysts can eventually rupture, leading to the leakage of blood, pus, and eggs into the lung tissue.
Symptoms and Clinical Presentation
Symptoms typically emerge two to eight weeks after the initial infection. Because many symptoms overlap with other conditions, accurate diagnosis is critical.
Common Symptoms
Symptom Type | Specific Signs |
Respiratory | Persistent dry cough, progressing to rusty-colored or blood-tinged mucus; chest pain. |
Systemic | Fever, fatigue, and unintended weight loss. |
Digestive | Abdominal pain and diarrhea (often occurring in the early stages). |
Cutaneous | Bumps under the skin of the abdomen that may move toward the chest. |
Cerebral Paragonimiasis
In some cases, the infection spreads to the central nervous system, including the brain and spine. This form of the disease is more severe and can be fatal in 5% of untreated cases. Symptoms include:
Seizures and severe headaches.
Blurred or double vision.
Confusion and muscle weakness.
Neck stiffness and vomiting.
Diagnosis and Diagnostic Tests
Healthcare providers use a combination of laboratory tests and imaging to confirm the presence of Paragonimus flukes.
Diagnostic Procedures
Microscopic Examination: Looking for parasite eggs in sputum (mucus), stool (poop), or fluid from around the lungs.
Imaging: Chest X-rays, CT scans, and MRIs are used to visualize cysts or damage in the lungs and other organs.
Blood Tests: Testing for specific antibodies to the fluke or signs of a secondary bacterial infection.
Biopsy: In cases of cutaneous paragonimiasis, a skin biopsy may be performed to identify the parasite.
Treatment and Recovery
Paragonimiasis is highly curable with modern medical intervention. Most patients respond well to a short course of oral medication.
Medication | Usage and Effectiveness |
Praziquantel | The primary treatment, often curing 86% to 100% of cases within 1 to 3 days. |
Triclabendazole | An alternative antiparasitic medication used to eliminate the flukes. |
Corticosteroids | Used specifically for cerebral paragonimiasis to reduce brain inflammation. |
Surgery | Rarely required, but may be used to remove large or persistent cysts. |
Prevention and Safety
The most effective way to prevent paragonimiasis is to ensure that all crustaceans are thoroughly cooked before consumption.
Prevention Tips
Avoid Raw Shellfish: Never eat raw, pickled, or salted crab or crayfish.
Cook Thoroughly: Ensure crab and crayfish are cooked to safe internal temperatures.
Safe Preparation: Avoid using raw crab juice or marinating crustaceans in wine ("drunken" crab) as a substitute for cooking.
Emergency Warning: Seek immediate medical attention at an emergency room if you experience a high fever (above 103°F), severe chest pain, seizures, or if you begin coughing up blood.
Frequently Asked Questions
1. What exactly is a lung fluke?
A lung fluke is a type of parasitic flatworm from the genus Paragonimus that primarily infects the lungs of humans and other animals.
2. Can I get paragonimiasis from another person?
No, the infection is not contagious and cannot be spread from person to person.
3. How soon do symptoms appear after eating contaminated food?
Symptoms typically develop between two weeks and two months after ingestion.
4. Why is it often confused with tuberculosis?
Both conditions cause chronic cough, chest pain, and coughing up blood, making them clinically similar without specific testing.
5. Is paragonimiasis found in the United States?
Yes, species of Paragonimus exist in parts of the U.S. and Canada, though it is more prevalent in Asia, Africa, and Latin America.
6. What is "drunken crab," and is it safe?
Drunken crab is crab marinated in wine. It is not safe because the alcohol does not kill the parasite larvae; only thorough cooking is effective.
7. What happens if the infection reaches the brain?
Known as cerebral paragonimiasis, this can cause seizures, vision problems, and confusion. It is fatal in about 5% of untreated cases.
8. How do doctors find the eggs?
Doctors examine samples of sputum, stool, or tissue under a microscope to identify the characteristic eggs of the fluke.
9. How long does the treatment last?
Treatment is usually very short, typically lasting between one and three days of oral medication.
10. Can the infection come back after treatment?
If the initial course of medication does not kill all the flukes, symptoms may return, requiring a second round of treatment.
11. Are there bumps on the skin associated with this?
Yes, cutaneous paragonimiasis can cause painful bumps under the skin of the abdomen that may move upward.
12. Can paragonimiasis cause permanent lung damage?
If left untreated, it can lead to complications like pneumonia, lung abscesses, and bronchiectasis (permanent damage to the airways).
13. Is the medication for this expensive or hard to find?
Antiparasitic medications like praziquantel are standard treatments and are generally available through healthcare providers.
14. Should I see a doctor if I ate undercooked crab but have no symptoms?
Yes, it is wise to consult a provider and mention the exposure, as symptoms can take weeks to develop.
15. Is there a vaccine for paragonimiasis?
No, there is currently no vaccine. Prevention relies entirely on safe food preparation and avoiding raw crustaceans.
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Medical Disclaimer: This content is for informational purposes only and does not constitute medical advice. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.
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