Flukes (Trematodes)

Snapshot

• A 15-year-old boy presents to the emergency room for a 2-month history of shortness of breath on exertion and cough. He recently moved from Laos to the United States for school. He reports having an unintentional 8-lb weight loss in the past few months, occasional fevers, and night sweats. He also reports having occasional hemoptysis. Prior to immigrating, he had a normal tuberculin skin test. A chest radiograph shows a linear streak and right-sided consolidation. A sputum sample is procured and sent for microscopy, which demonstrates oval-shaped eggs. (Paragonimiasis)

Introduction

• Introduction
  • flukes are parasitic trematodes
    • characteristics
      • possess 2 suckers (trematos = “pierced with holes”)
      • unsegmented and flattened worms
    • blood fluke
      • Schistosoma species
    • liver fluke
      • Clonorchis sinensis
    • lung fluke
      • Paragonimus species
• Treatment
• praziquantel  

Schistosoma

• Schistosoma species (blood flukes)
  • organisms
    • Schistosoma haematobium (Africa and Middle East)
      • causes genitourinary tract disease
    • Schistosoma mansoni (Africa and South America)
      • causes intestinal tract and hepatosplenic disease
    • Schistosoma japonicum (East Asia)
      • causes intestinal tract and hepatosplenic disease
  • epidemiology
    • most occur in sub-Saharan Africa
  • transmission
    • snails are intermediate hosts
    • via penetration of skin
  • risk factors
    • exposure to fresh water
    • farming
• Presentation
  • Katayama fever 
    • fevers, hives, weight loss, and cough
    • acute illness after initial infection
  • chronic infections
    • S. mansoni and S. japonicum
      • hepatosplenomegaly with fibrosis and inflammation
        • portal hypertension
      • intestinal tract infection
        • abdominal pain
        • diarrhea
    • S. haematobium
      • squamous cell bladder cancer
        • hematuria (classic symptom)
        • dysuria
• Studies
  • microscopy of urine or stool
    • S. haematobium 
      • eggs with terminal spine
    • S. mansoni and S. japonicum
      • eggs with lateral spine
  • serology or PCR within 2 months of exposure
  • eosinophilia
• Complications
  • portal hypertension
  • bladder stones
• squamous cell bladder cancer

Clonorchis

• Clonorchis sinensis (liver flukes)
  • epidemiology
    • east Asia
    • Russia
  • transmission 
    • via ingestion of undercooked, dried, or pickled fish
  • pathogenesis
    • causes biliary tract inflammation
• Presentation
  • chronic symptoms
    • right upper quadrant abdominal pain
    • anorexia
    • weight loss
    • diarrhea
    • jaundice
  • cholecystitis
  • ascending cholangitis
  • cholelithiasis with pigmented gallstones
• Studies
  • microscopy of stool
    • flask-shaped C. sinensis eggs
  • eosinophilia
  • elevated alkaline phosphatase
• Complications
• cholangiocarcinoma

Paragonimus

• Paragonimus species (lung flukes)
  • organisms
    • Paragonimus westermani (east Asia, Africa, and South America)
    • Paragonimus heterotremus (India)
  • transmission
    • via ingestion of undercooked crabs or crayfish
  • pathogenesis
    • inhabits lung parenchyma by penetrating through intestinal wall and peritoneal cavity to diaphragm
• Presentation
  • tuberculosis-like illness
    • pleural effusion
    • pleuritic chest pain
    • recurrent bacterial pneumonia
    • hemoptysis
    • shortness of breath
    • fever, weight loss, and night sweats
• Imaging
  • chest radiograph
    • consolidations
    • “ring shadow” of an oval thin-walled cyst
    • linear streak or fluke tract
• Studies
  • microscopy of sputum or stool 
    • ovoid and thick-shelled Paragonimus eggs
• Complications
  • pulmonary abscess