Indications for Testing

• History of exposure to fresh water in endemic area and evidence of associated hematuria

Laboratory Testing

• Non-specific testing
  • CBC – blood eosinophilia may be supportive evidence (average of ~50 days between infection and eosinophilia)
• Microscopic examination of viable eggs in urine, feces or tissue
  • 30-50 days delay between exposure to contaminated water and appearance of eggs
  • Stool exam performed when S. mansoni or S. japonicum suspected; urine exam when S. haematobium suspected
• ELISA IgG testing – may aid in diagnosis of schistosomiasis in patients from non-endemic areas
  • Seroconversion lags symptoms by ~3 weeks

Histology

• Histopathology (colon, bladder, lung) demonstrating Schistosoma eggs when stool or urine examinations are negative

Differential Diagnosis

• Acute
  • Entamoeba histolytica
  • Rickettsia typhi
  • Diarrhea – parasitic, viral, bacterial
  • Plasmodium spp
  • Leishmania spp
  • Meningitis
  • Encephalitis
  • Hypersensitivity pneumonitis
• Chronic
  • Meningitis
  • Cirrhosis
  • Inflammatory bowel disease
  • Bladder cancer

Schistosomiasis (bilharziasis), an endemic parasitic tropical disease found especially in sub-Saharan Africa, causes substantial morbidity and mortality. In developed countries, the disease is typically seen in nonimmune travelers returning from endemic areas.

Epidemiology

• Prevalence – >200 million people world-wide are infected
• Age – highest prevalence in children
• Transmission – from water with snails, which serve as intermediate hosts
  • Common in South America, Africa, Southeast Asia and the Middle East
  • In Europe, ~2% of febrile travelers returning from abroad are eventually diagnosed with schistosomiasis

Organism

• Human infection is caused by Schistosoma spp, a digenetic blood trematode of the Schistosomatidae family
• Common schistosomes that infect humans
  • S. mansoni – Africa, Latin America
  • S. haematobium – Middle East, Africa
  • S. japonicum – East Asia, Pacific
  • S. intercalatum – sub-Saharan Africa
  • S. mekongi – Cambodia, Laos
• Parasite has a complex life cycle and requires an intermediate-stage host (for more information on life cycle, causal agents and geographic distribution, see CDC's information on schistosomiasis)
  • Miracidium infect freshwater snails that later release cercariae back into the water; cercariae then infect human and animal hosts

Risk Factors

• Rural areas with inadequate sanitation and contaminated water supplies

Clinical Presentation

• Schistosome dermatitis (known as swimmer's itch)
  • From Schistosoma spp cercariae that infect birds or aquatic mammals
  • Common in the Great Lakes region, New England and other parts of the U.S.
    • Only brief contact (1-5 minutes) with infected water is necessary
  • Itchy macular rash caused by cercaria entering the skin and dying
  • Self-limited (humans are a “dead-end” host for non-human schistosomes)
• Acute schistosomiasis (also known as Katayama syndrome or fever)
  • Systemic hypersensitivity reaction; may occur 2-8 weeks after infection
  • Fever, myalgia, nonproductive cough, fatigue, abdominal pain, eosinophilia and occasionally bloody stools
  • Liver, spleen and lymph nodes are often enlarged
  • Eggs may not be seen in stools until late in the illness
  • Death can occur in severe cases
• Chronic schistosomiasis
  • Symptoms may be absent or mild especially in patients with light or moderate egg burden
  • Peripheral blood – eosinophilia is often present
  • Fatigue, colicky abdominal pain, intermittent diarrhea or dysentery
  • Anemia due to blood loss
  • Species-specific symptoms and diseases
    • Periportal fibrosis which may lead to hepatic failure – S. mansoni and S. japonicum
    • Hematuria and dysuria – S. haematobium
      • In later stages of the disease, fibrosis of the bladder may occur which can lead to renal failure and squamous cell cancer of the bladder
    • Neurologic disease (all human Schistosoma)
      • Brain infection – meningitis, encephalitis
      • Myelopathy (most common sites are conus medullaris and cauda equina)

Treatment

• Indicated for all patients with schistosomiasis
• Anthelminthic agents such as praziquantel are used but are only marginally effective
  • Oxamniquine – has been effective in treating infections caused by S. mansoni in areas where praziquantel is less effective

Prevention

• Avoid contact with fresh water in endemic areas
• DEET 50% ointment may be beneficial against cercariae if applied before contact with water

Tests generally appear in the order most useful for common clinical situations

General

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• Chitsulo L, Loverde P, Engels D. Schistosomiasis. Nat Rev Microbiol. 2004; 2 (1) :12-13.PubMed
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Bladder Cancer
Churg-Strauss Syndrome
Cirrhosis
Encephalitis, Infectious
Hypersensitivity Pneumonitis
Meningitis, Acute