Schistosoma Species - Schistosomiasis

  • Diagnosis
  • Background
  • Lab Tests
  • References
  • Related Topics

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 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

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

  • 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
      • 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
      • Malaria – may increase morbidity for liver disease, increase risk of hepatocellular carcinoma
      • HBV – causes worse liver disease in S. mansoni and S. japonicum
      • HCV – more severe liver disease
      • HIV – suggested that S. haematobium increases risk of HIV transmission
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.

Ova and Parasite Exam, Fecal (Immunocompromised or Travel History) 2002272
Method: Qualitative Concentration/Trichrome Stain/Microscopy

Limitations 

Ova may not be detectable in early disease 

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

Schistosoma Antibody, IgG 0099411
Method: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Limitations 

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

General References

Colley DG, Bustinduy AL, Secor E, King CH. Human schistosomiasis. Lancet. 2014; 383(9936): 2253-64. PubMed

Gray DJ, Ross AG, Li Y, McManus DP. Diagnosis and management of schistosomiasis. BMJ. 2011; 342: d2651. PubMed

Gryseels B, Polman K, Clerinx J, Kestens L. Human schistosomiasis. Lancet. 2006; 368(9541): 1106-18. PubMed

Jauréguiberry S, Paris L, Caumes E. Acute schistosomiasis, a diagnostic and therapeutic challenge. Clin Microbiol Infect. 2010; 16(3): 225-31. PubMed

Lewis FA, Tucker MS. Schistosomiasis. Adv Exp Med Biol. 2014; 766: 47-75. PubMed

Ross AG, Vickers D, Olds R, Shah SM, McManus DP. Katayama syndrome. Lancet Infect Dis. 2007; 7(3): 218-24. PubMed

Medical Reviewers

Last Update: September 2016