Diagnostic dilemma: Woman develops rare parasitic lung infection after eating raw frog

Patient: 32-year-old female living in Shanghai

Symptoms: A woman presented to the hospital with a persistent cough that occasionally produced bloody sputum, and coughed 2 to 3 times a day. She said the cough started four months before she visited the hospital. Then, about a month before the cough started, she developed a fever that lasted several weeks and reached a high of 100.8 degrees Fahrenheit (38.3 degrees Celsius).

What happened next: Doctors at the hospital diagnosed the woman with a rare respiratory disease called eosinophilic pneumonia. Eosinophilic pneumonia is an infection in which white blood cells accumulate in the lungs, causing inflammation. If left untreated, the infection can damage the lungs and sometimes lead to death.

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The patient’s doctor gave him steroids to reduce inflammation in his lung tissue. However, even after two months of this treatment, her cough persisted. A CT scan of her lungs revealed recurrent lesions or tissue damage, so she was sent to another hospital for further tests.

Diagnosis: Doctors at the second hospital reviewed the woman’s medical history and reported that her diet often included raw seafood and that she had a “preference for raw frogs and bullfrogs,” doctors wrote in a report describing her case. The researchers ran a blood test to see if her blood contained antibodies to the parasite, and found antibodies to the larvae of the tapeworm, Mansoni spirometra.

The larvae of Schistosoma mansoni, or Spargana, cause a parasitic infection called sparganosis. The infection is most common in East Asia, where evidence suggests that people become infected with the parasite by eating raw or undercooked snakes or frogs infected with the larvae. After being swallowed, Schistosoma mansoni larvae migrate to various body tissues and organs. In the woman’s case, it was a very rare destination for the parasite to accumulate in her lungs.

The patient provided doctors with a frog he collected in Shanghai, and upon dissection, it was discovered that it was infested with Schistosoma mansoni.

Doctors who examined her during her first visit misdiagnosed her because her symptoms and CT scan results closely resembled signs of eosinophilic pneumonia, the report said.

Treatment: Doctors treated the woman with praziquantel tablets, a drug that works against various types of parasites. After the woman took the tablets for five days, her cough subsided.

A CT scan performed 20 days after admission to the second hospital showed that the shadow areas previously seen in the lungs (a sign of infection or physical trauma) had shrunk. At a follow-up visit one month later, the cough had completely disappeared. However, blood tests on the patient showed that the patient was still producing antibodies against the parasite, suggesting that the infection was continuing.

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Doctors prescribed another five days of praziquantel and a follow-up test five months later. There were traces of antibodies left in the patient’s blood, but the amount was extremely small. Her white blood cell count was normal, and doctors determined no further treatment was needed.

Characteristics of this case: Sparganosis infections usually occur in tissues near the surface of the body, just beneath the skin. It rarely migrates to internal organs. This is the first case of pulmonary sparganosis recorded in Shanghai, the case report authors wrote.

Eating raw animal meat is a long-standing cultural tradition in some parts of Asia, and sometimes small animals are eaten alive. Live frogs are sometimes eaten as a folk remedy for various ailments. An 82-year-old woman in Hangzhou was hospitalized with a parasitic infection after swallowing eight small live frogs to relieve chronic back pain.

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