Schistosoma Species - Schistosomiasis

Diagnosis

Indications for Testing

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

Laboratory Testing

  • Nonspecific testing
    • CBC – blood eosinophilia may be supportive evidence
      • Average of ~50 days between infection and eosinophilia
  • Microscopic examination for 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 nonendemic areas
    • Unable to discriminate between active infection and past exposure
    • Generally negative at onset of clinical symptoms
      • Seroconversion occurs ~30 days after symptoms and ~6 weeks after contact with contaminated water

Differential Diagnosis

Clinical Background

Schistosomiasis (sometimes called 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 – >300 million people worldwide 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 caused by Schistosoma spp, a digenetic blood trematode of the Schistosomatidae family
  • Common schistosomes that infect humans – snails as the intermediate host
    • S. mansoni – Africa, Latin America
    • S. haematobium – Middle East, Africa
    • S. japonicum – East Asia, Pacific
    • S. intercalatum, S. guineansis – sub-Saharan Africa
    • S. mekongi – Cambodia, Laos
  • Other schistosome spp that infect birds or aquatic mammals
    •  Schistosoma spp cercariae – common in the Great Lakes region, New England, and other parts of the U.S.; causes schistosome dermatitis (known as "swimmer’s itch")
  • Parasite has a complex life cycle and requires an intermediate-stage host 
    • Miracidia infect freshwater snails that later release cercariae back into the water
    • Cercariae then infect human and animal hosts
    • For more information on life cycle, causal agents, and geographic distribution, see CDC's information on schistosomiasis

Risk Factors

  • Rural areas with inadequate sanitation and contaminated water supplies

Clinical Presentation

  • Schistosome dermatitis (swimmer’s itch)
    • Only brief contact (1-5 minutes) with infected water is necessary
    • Itchy macular rash caused by cercariae entering the skin and dying
    • Self-limited – humans are a “dead-end” host for nonhuman-pathogenic schistosomes
  • Acute schistosomiasis (also known as schistosomiasis japonica or Katayama syndrome or fever)
    • Systemic hypersensitivity reaction – may occur 2-8 weeks after infection
    • Fever, myalgia, nonproductive cough, fatigue, abdominal pain, eosinophilia, occasionally bloody stools
    • Liver, spleen, and lymph nodes often enlarged
    • 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 often present
    • Fatigue, abdominal pain, intermittent diarrhea, or dysentery
    • Anemia due to blood loss
    • Species-specific symptoms and diseases
      • Periportal fibrosis, which may lead to hepatic failureS. 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-pathogenic Schistosoma)
        • Brain infection – meningitis, encephalitis
        • Myelopathy (most common sites are conus medullaris and cauda equina)

Indications for Laboratory Testing

  • Tests generally appear in the order most useful for common clinical situations
  • Click on number for test-specific information in the ARUP Laboratory Test Directory
Test Name and Number Recommended Use Limitations Follow Up
CBC with Platelet Count and Automated Differential 0040003
Method: Automated Cell Count/Differential
Nonspecific testing to determine presence of eosinophilia    
Ova & Parasite Exam, Fecal (Immunocompromised or Travel History) 2002272
Method: Qualitative Concentration/Trichrome Stain/Microscopy

Order only if patient has defined risk factor (ie, history of travel or residence in endemic area, exposure history, immunocompromised state, or high pretest probability for parasitic infection) and at least 3 days of persistent diarrhea

Identifies ova or parasites (eg, Giardia duodenalis, Entamoeba histolytica, helminth eggs, protozoa, larval worms, and segments of tapeworms)

Sensitivity improved with three stool samples collected on separate days

Do not order for patients who develop diarrhea during an inpatient stay

Ova may not be detectable in early disease

Less sensitive than stool antigen tests for Giardia duodenalis, Cryptosporidium spp, or Entamoeba histolytica

In patients with negative O & P and persistent diarrhea, follow up negative stool antigen EIA result for Giardia duodenalis (synonym Giardia intestinalis, Giardia lamblia), Cryptosporidium spp, or Entamoeba histolytica

For Cryptosporidium, refer to the Cryptosporidium Antigen by EIA test; for Cyclospora and Cystoisospora, refer to Parasitology Stain by Modified Acid-Fast; for Microsporidia, refer to Microsporidia Stain

Ova and Parasite Exam, Body Fluid or Urine 2002277
Method: Qualitative Concentration/Microscopy

Diagnose schistosomiasis caused by S. haematobium

Use urine specimen

   
Schistosoma Antibody, IgG 0099411
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay
May aid in the diagnosis of schistosomiasis in patients from nonendemic areas when stool and urine tests are negative

Overall sensitivity 97%; specificity 92%

Sensitivity for S. japonicum <50%

Sensitivity for S. haematobium 95%

False-positive results due to cross-reactivity may occur in samples positive for malaria, filariasis, Toxocara, Leishmania, Epstein-Barr virus

Single test cannot distinguish active from past infection