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 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 nonendemic areas
- Generally negative at onset of clinical symptoms
  - Seroconversion occurs ~30 days after symptoms and ~6 weeks after contact with contaminated water
- Single test cannot distinguish active from past infection

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

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 – >200 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
- S. mansoni – Africa, Latin America
- S. haematobium – Middle East, Africa
- S. japonicum – East Asia, Pacific
- S. intercalatum – 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
- Miracidium 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 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, 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, 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)

Prevention

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

Tests

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

Test name: CBC with Platelet Count and Automated Differential

ARUP #: 0040003

Methodology: Automated Cell Count/Differential

Use: Nonspecific testing to determine presence of infectious process, eosinophilia

Test name: Ova & Parasite Exam, Fecal (Immunocompromised or Travel History)

ARUP #: 2002272

Methodology: Qualitative Concentration/Trichrome Stain/Microscopy

Use:

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

Limitations:

Ova may not be detectable in early disease

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

Follow-up:

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

Test name: Ova and Parasite Exam, Body Fluid or Urine

ARUP #: 2002277

Methodology: Qualitative Concentration/Microscopy

Use:

Diagnose schistosomiasis caused by S. haematobium

Use urine specimen

Test name: Schistosoma Antibody, IgG

ARUP #: 0099411

Methodology: Semi-Quantitative Enzyme-Linked Immunosorbent Assay

Use: May aid in the diagnosis of schistosomiasis in patients from nonendemic areas when stool and urine tests are negative

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

References

General

Medical Reviewers

Couturier, Marc Roger, PhD, D(ABMM). Medical Director Microbial Immunology, and Assistant Medical Director Parasitology/Fecal Testing and Infectious Disease Rapid Testing at ARUP Laboratories; Assistant Professor of Pathology, University of Utah

Comprehensive Review: June 2012
Last Update: March 2013