Paragonimus infection overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Paragonimus is a parasitic lung fluke (flat worm). Cases of infection occur after a person eats raw or undercooked infected crab or crayfish. Paragonimus infection also can be very serious if the fluke travels to the central nervous system, where it can cause symptoms that mimic meningitis.
Causes
Paragonimus infection is caused by more than 30 species of trematodes (flukes) of the genus Paragonimus which infect animals and humans. Among the species reported to infect humans, the most common is P. westermani, the oriental lung fluke.
Epidemiology and Demographics
Paragonimus spp. are distributed throughout the Americas, Africa and southeast Asia. Paragonimus westermani is distributed in southeast Asia and Japan. Paragonimus kellicotti is endemic to North America.
Differentiating Paragonimus infection from other Diseases
The clinical picture of chronic paragonimiasis resembles chronic bronchitis or tuberculosis. Persons may cough up coffee-colored or blood-tinged sputum, often accompanied by chest pain and/or shortness of breath.
Natural History, Complications and Prognosis
Paragonimiasis is an acute infection with cough, abdominal pain, discomfort, and low-grade fever that may occur 2 to15 days after infection. The infection usually resolves without treatment. Persons with light infections may have no symptoms. Symptoms of long-term infection may mimic bronchitis or tuberculosis, with coughing up of blood-tinged sputum. CNS involvement occurs in up to 25% of hospitalized patients and may be associated with Paragonimus-induced meningitis.
Diagnosis
Laboratory Findings
Diagnosis is based on microscopic demonstration of eggs in stool or sputum, but these are not present until 2 to 3 months after infection. (Eggs are also occasionally encountered in effusion fluid or biopsy material.) Concentration techniques may be necessary in patients with light infections. Biopsy may allow diagnostic confirmation and species identification when an adult or developing fluke is recovered.
Chest X Ray
Many patients have a spectrum of abnormalities on chest radiographs: lobar infiltrates, coin lesions, cavities, calcified nodules, hilar enlargement, pleural thickening and effusions. Ring-shaped opacities of contiguous cavities giving the characteristic appearance of a bunch of grapes are highly suggestive of pulmonary paragonimiasis.
CT
Central nervous system disease may provide similar "grapebunch" findings, characteristically seen in the temporal and occipital lobes on computed tomography of the brain.
Treatment
Medical Therapy
Praziquantel is the drug of choice to treat paragonimiasis. Bithionol is an alternative drug for treatment of this disease.
Primary Prevention
Never eat raw freshwater crabs or crayfish. Cook crabs and crayfish for to at least 145°F (~63°C). Travelers should be advised to avoid traditional meals containing undercooked freshwater crustaceans.
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