Schistosoma Species - Schistosomiasis

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.

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 development of 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 Schistosoma mansoni or S. japonicum suspected
    • Urine exam when S. haematobium suspected
  • Enzyme-linked immosorbent assay (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

Background

Epidemiology

  • Prevalence – >240 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

  • Common schistosomes that infect humans – snails as the intermediate host
    • Schistosoma 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
      • Fatigue due to anemia because of blood loss
    • Species-specific symptoms and diseases
      • Periportal fibrosis, which may lead to hepatic failureS. mansoni and S. japonicum most common
      • Chronic ulceration and bleeding – S. mansoni and S. japonicum most common
      • 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)
    • Coinfection with

ARUP Laboratory Tests

If parasite infection is suspected as cause of persistent diarrhea (>14 days), specific pathogen testing is recommended; refer to gastrointestinal parasite panel by PCR; giardia antigen by EIA; Entamoeba histolytica antigen by EIA; or Cryptosporidium antigen by EIA

Do not order for patients who develop diarrhea during a prolonged hospitalization

Due to the various shedding cycles of many parasites, 3 separate stool specimens collected over a 5- to 7-day period are recommended for ova and parasite examination

A single negative result does not rule out the possibility of a parasitic infection

Detect extraintestinal parasites from other body fluids

For cerebrospinal fluid (CSF) specimens, consider ordering culture with stain test for Acanthamoeba spp and Naegleria fowleri

Aid in the diagnosis of schistosomiasis

Positive results in patients from endemic areas may not represent active infection

Related Tests

Nonspecific testing to determine presence of eosinophilia

Medical Experts

Contributor

Couturier

Marc Roger Couturier, PhD, D(ABMM)
Associate Professor of Clinical Pathology, University of Utah
Medical Director, Parasitology/Fecal Testing, Infectious Disease Antigen Testing, Bacteriology, and Molecular Amplified Detection, ARUP Laboratories
Contributor

Slev

Patricia R. Slev, PhD
Associate Professor of Clinical Pathology, University of Utah
Section Chief, Immunology; Medical Director, Immunology Core Laboratory, ARUP Laboratories
Medical Director, Serologic Hepatitis and Retrovirus and Immunology Core Laboratory
Co-Medical Director, Microbial Immunology, at ARUP Laboratories

References

Additional Resources