A Diagnostic Dilemma: Rare Parasitic Lung Infection Linked to Eating Raw Frogs
The patient: A 32-year-old woman from Shanghai.
The symptoms: She visited the hospital with a persistent cough and occasional bloody sputum, coughing up material two to three times daily. The coughing began four months before her hospital visit. About a month prior, she had a fever that lasted several weeks, reaching as high as 38.3°C (100.8°F).
Initial treatment focused on reducing lung inflammation with steroids. Despite two months of this therapy, the cough persisted. A CT scan revealed recurring lung lesions, prompting a transfer to another hospital for further investigation.
The diagnosis: Reviewing her medical history at the second hospital revealed a pattern of consuming raw seafood and, notably, a preference for raw frogs and bullfrogs. Blood tests showed antibodies against parasite larvae, specifically Spirometra mansoni, a tapeworm species. The larvae form, known as spargana, cause sparganosis. This infection is more common in eastern Asia, and transmission often occurs when ingesting raw or undercooked snakes or frogs carrying the larvae. After ingestion, the larvae migrate through various tissues and organs; in this case, they collected in the lungs—a particularly unusual site for sparganosis.
When doctors examined a frog from the patient’s region of Shanghai, dissection confirmed the frog carried S. mansoni.
Clinical reasoning and diagnostic challenge: The patient’s symptoms and CT findings closely resembled eosinophilic pneumonia, leading to an initial misdiagnosis during the first hospital visit.
The treatment: The patient received praziquantel, a broad-spectrum antiparasitic medication. After five days of therapy, her coughing diminished. Follow-up CT scans 20 days after admission showed shrinking shadows in the lungs, and a month later, the cough had completely resolved. However, antibody tests remained positive, suggesting ongoing exposure or a lingering infection.
A subsequent five-day course of praziquantel was prescribed, and a five-month follow-up showed only very low antibody levels. White blood cell counts were normal, and no further treatment was deemed necessary.
Other dilemmas and notable points:
- Unusual presentation: Sparganosis typically targets subcutaneous tissues and skin-adjacent areas. Lung involvement is rare, and this case represents the first documented instance of sparganosis in the lungs in Shanghai.
- Cultural context: Eating raw animal flesh is a traditional practice in parts of Asia. In some cases, people may consume live animals or raw products to address various ailments. There are reports of other severe parasitic infections linked to unconventional remedies, such as a separate case in Hangzhou where an elderly woman ingested live frogs to treat back pain.
For more cases and updates, see Live Science’s Diagnostic Dilemma collection.
Disclaimer: This summary is for informational purposes only and does not constitute medical advice.
About the author: Mindy Weisberger is a science journalist and author, with extensive experience reporting on parasitology, biology, and related fields. Her work spans publications like Scientific American, The Washington Post, How It Works Magazine, and CNN, and she has contributed to museum and science-center programs worldwide.
