Diagnostic dilemma: A woman got a rare parasitic lung infection after eating raw frogs

The patient: A 32-year-old woman in Shanghai

The symptoms: The woman went to the hospital with a persistent cough accompanied by occasional bloody phlegm, which she would cough up two to three times per day. She said the coughing began four months prior to her hospital visit. And about a month before the coughing started, she had a fever that lasted several weeks and reached up to 100.8 degrees Fahrenheit (38.3 degrees Celsius).

What happened next: Doctors at the hospital diagnosed the woman with a rare respiratory illness called eosinophilic pneumonia, an infection in which white blood cells accumulate in the lungs and cause inflammation. If left untreated, the infection can damage the lungs, and in some cases, it can be fatal.

The patient's doctors gave her steroids to reduce the inflammation in her lung tissue. However, her cough persisted even after two months of this treatment. A CT scan of her lungs revealed recurring lesions, or tissue injuries, and she was then sent to a different hospital for further examination.

The diagnosis: When doctors at the second hospital reviewed the woman's medical history, they noted that her diet often included raw seafood, and she also reported "a preference for raw frogs and bullfrogs," the physicians wrote in a report describing her case. The team conducted a blood test to see if her blood contained antibodies to any parasites, and they found antibodies for the larvae of Spirometra mansoni, a type of tapeworm.

The larvae, or spargana, of S. mansoni cause a parasitic infection called sparganosis. This infection is most common in eastern Asia, and people often acquire the parasites by eating raw or undercooked snakes or frogs that are infected with the larvae, evidence suggests. After S. mansoni larvae are swallowed, they migrate into various body tissues and organs. In the woman's case, they accumulated in her lungs — a very rare destination for the parasite.

When the patient provided doctors with a frog from her region of Shanghai, they dissected it and found that it was carrying S. mansoni.

Because the woman's symptoms and the results of her CT scans closely resembled signs of eosinophilic pneumonia, the physicians who examined her during her first hospital visit misdiagnosed her, according to the report.

The treatment: Doctors treated the woman with praziquantel tablets, a drug that works against various types of parasitic worms. After the woman had taken the tablets for five days, her coughing subsided.

CT scans performed 20 days after her admission to the second hospital showed that the shadowy areas previously seen in her lungs — a sign of infection or physical trauma — were shrinking. At a follow-up visit one month later, her coughing was completely gone. However, the patient's blood tests showed that she was still producing antibodies against the parasite, hinting that the infection persisted.

Doctors prescribed another five-day course of praziquantel and conducted a follow-up examination five months after that. Traces of antibodies remained in the patient's blood, but only in extremely low quantities. Her white blood cell count was normal, and the doctors determined that no further treatment was required.

What makes the case unique: Sparganosis infections typically appear in tissues located just under the skin, near the surface of the body. They rarely migrate to the internal organs. This is the first case to be documented in Shanghai of sparganosis in the lungs, the case report authors wrote.

Eating raw animal flesh is a long-standing cultural tradition in parts of Asia, and sometimes, small animals may be consumed while they are still alive. Living frogs are occasionally eaten as a folklore remedy for a variety of ailments; an 82-year-old woman in Hangzhou was hospitalized with a parasitic infection after she swallowed eight small, live frogs in an attempt to relieve her chronic back pain.

For more intriguing medical cases, check out our Diagnostic Dilemma archives.