Quiz Answer

Paragonimiasis—The chest CT revealed a 4-mm pulmonary cavity, with surrounding infiltrate in the left lower lobe (Figure). Human paragonimiasis is a subacute or chronic infection, usually of the lungs, caused by Paragonimus species. The patient's ELISA for immunoglobulin (Ig) G titer against Paragonimus was 1:64 (ie, positive). Microscopic examination of the bronchial wash specimen was negative for eggs of Paragonimus.

Figure—Chest CT scan revealing a 4-mm pulmonary cavity and surrounding infiltrate (arrow).

Nine Paragonimus species are known to infect humans¹; among these are Paragonimus westermani in the Far East and Southeast Asia, Paragonimus africanus in West Africa, Paragonimus mexicanus  in Central and South America, and Paragonimus kellicotti  in North America.² Paragonimiasis is common in Asia, some parts of Latin America, and West Africa. The disease is increasingly being seen in many parts of the world, as a result of greater overseas travel.³

Humans are infected by ingesting raw or undercooked crabs and crayfish that harbor metacercariae of Paragonimus. The metacercariae migrate from the human duodenum into the peritoneal cavity, to the pleural space, and then to the lungs, where they mature to adult worms and deposit their eggs. Infection can also result from ingestion of raw meat from wild boars and pigs that harbor juvenile worms.⁴ Our patient visited Nepal and Thailand for months, where he often ate cooked seafood in the streets. The only raw food he ate was sushi in Thailand. We think he most likely ate undercooked food that contained Paragonimus metacercariae.

The classic symptoms of pulmonary paragonimiasis include a chronic cough, with rusty-brown sputum, hemoptysis, pleurisy, and fever, with variable radiographic findings, including patchy density, linear infiltration, nodules, pleural effusion, and pulmonary cavities. Patients are often misdiagnosed as having pulmonary TB or lung cancer and undergo unnecessary diagnostic procedures.³ Cutaneous and cerebral paragonimiasis are among the well-recognized extrapulmonary manifestations. A slow-moving cutaneous nodule is a characteristic sign, frequently seen on the abdomen or the anterior chest wall.

A definitive diagnosis of paragonimiasis is made when parasite eggs are detected in sputum, feces, or in histologic sections,^2,4 but egg detection rates are low. Serologic testing for antiparagonimus IgG by ELISA has a sensitivity of 100% and specificity of 91% to 100%.⁵

The treatment of choice is praziquantel, 25 mg/kg 3 times daily for 3 consecutive days, with a cure rate close to 100%.¹ Following this treatment regimen, our patient had no recurrence in the next 3 months.

Three negative sputum smears and a negative culture make Mycobacterium tuberculosis infection unlikely. In addition, reactivated TB in immunocompetent hosts usually involves the upper lobes, and the cavities have thicker walls compared with those of paragonimiasis. The absence of immunosuppression and the occurrence of hemoptysis as the only manifestation rule out invasive aspergillosis; in addition, our patient's CT scan is not typical of aspergilloma. Lung cancer is unlikely in this nonsmoking young patient.

References

1. Velez ID, Ortega JE, Velasquez LE. Paragonimiasis: a view from Columbia. Clin Chest Med. 2002;23:421-431.
2. Castillo AE, Jessen R, Sheck D, et al. Cavitary mass lesion and recurrent pneumothoraces due to Paragonimus kellicotti infection. Am J Surg Path. 2003;27:1157-1160.
3. Jeon K, Koh W, Kim H, et al. Clinical features of recently diagnosed pulmonary paragonimiasis in Korea. Chest. 2005;128:1423-1430.
4. Nakamura-Uchiyama F, Mukae H, Nawa Y. Paragonimiasis: a Japanese perspective. Clin Chest Med. 2002;23:409-420.
5. Narian K, Devi KR, Mahanta J. Development of enzyme-linked immunosorbent assay for serodiagnosis of human paragonimiasis. Indian J Med Res. 2005;121:739-746.