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For further information, see CMDT Part 35-16: Paragonimiasis

Key Features

Essentials of Diagnosis

  • Most persons are asymptomatic

  • In symptomatic cases, abdominal pain and diarrhea develop 2 days to 2 weeks after infection

  • Chronic infection produces pulmonary symptoms and chest pain

  • CNS disease presents with seizures, headaches, focal neurologic findings, intracerebral lesions

General Considerations

  • Of the eight species of Paragonimus lung flukes that cause human disease, Paragonimus westermani is the most important

  • Eggs are released into fresh water, where parasites infect snails, and then cercariae infect crabs and crayfish

  • Human infection follows consumption of raw, undercooked, or pickled freshwater shellfish

  • Metacercariae then excyst, penetrate into the peritoneum and pass into the lungs, where they mature into adult worms over about 2 months

Demographics

  • Paragonimus species are endemic in East Asia, Oceania, West Africa, and South America, where millions of persons are infected

  • Infections from Paragonimus kellicotti have occurred in North America, albeit rarely

Clinical Findings

Symptoms and Signs

  • Most persons have moderate worm burdens and are asymptomatic

  • In symptomatic cases,

    • Abdominal pain and diarrhea develop 2 days to 2 weeks after infection

    • Then, fever, cough, chest pain, urticaria, and eosinophilia develop

  • Acute symptoms may last for several weeks

  • Chronic infection can cause

    • Cough productive of brown sputum

    • Hemoptysis

    • Dyspnea

    • Chest pain

  • Ectopic infections can cause disease in other organs, most commonly the CNS

  • CNS disease can present with

    • Seizures

    • Headaches

    • Focal neurologic findings due to parasite meningitis

    • Intracerebral lesions

Differential Diagnosis

  • Tuberculosis

  • Mycoplasma pneumoniae infection

  • Bacterial pneumonia

  • Legionnaires disease (Legionella)

  • Amebic lung abscess

Diagnosis

Laboratory Tests

  • Diagnosis is made by identifying

    • Characteristic eggs in sputum or stool or

    • Worms in biopsied tissue

  • Multiple examinations and concentration techniques may be needed

  • Serologic tests may be helpful

  • An enzyme-linked immunosorbent assay (ELISA) available from the CDC has sensitivity and specificity > 95%

Imaging Studies

  • Chest radiographs may show

    • Infiltrates

    • Nodules

    • Cavitary lesions

    • Fibrosis

  • Skull radiographs can show clusters of calcified cysts

  • CT or MRI can show clusters of ring-enhancing lesions

Treatment

Medications

  • Praziquantel

    • Drug of choice

    • 25 mg/kg orally three times daily for 2 days

    • Use with corticosteroids for cerebral paragonimiasis

  • Bithionol and triclabendazole are alternative therapies

Outcome

Complications

  • Bronchitis

  • Bronchiectasis

  • Bronchopneumonia

  • Lung abscess

  • Pleural thickening or effusion

Prognosis

  • Cure rates of over 90% can be anticipated for praziquantel

When to Refer

  • All patients should be referred to a clinician with expertise in the diagnosis and management of this disease

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