Investigations

Seek expert advice.

Laboratory investigations:

• microscopic examination for schistosome eggs - should be carried out at least two months after the last known fresh water contact
  • in stools
    • by observing even a single egg in thick smears of stool specimens (2-10 mg) with or without suspension in saline
    • as many as three specimens may be needed to make a diagnosis in some patients
    • rapid, simple, and inexpensive Kato-Katz thick smear stool examination
      • recommended by WHO for intestinal schistosomiasis when the intensity of infection is high
      • requires 40-50 mg of faeces
      • has specificity of 100% but its sensitivity varies with prevalence and intensity of infection, as well as with the number of stool specimens collected and slides prepared for microscopy.
  • in urine
    • S haematobium eggs can be detected on microscopy in a urine sample concentrated by sedimentation, centrifugation, or filtration and forced over a paper or nitrocellulose filter
    • urine should ideally be collected when there is maximum excretion of eggs - between 10am-2pm
• PCR based assays for detection of schistosome DNA in faeces or sera and plasma
• biopsy of bladder or rectal mucosa - may be useful for diagnosis in patients with a typical clinical presentation of schistosomiasis in the absence of eggs in urine or faeces
• serological assays
  • detects antibodies against schistosomal antigens
  • most techniques detect IgG, IgM, or IgE against soluble worm antigen or soluble egg antigen by enzyme-linked immunosorbent assay (ELISA), indirect haemagglutination, or immunofluorescence.
  • useful for symptomatic travellers, but for people in endemic regions serology cannot differentiate between active infection and past exposure
  • positive test may be diagnostic in patients who are not excreting eggs e,g - Katayama syndrome
• additional supportive laboratory evidence of schistosomiasis include:
  • eosinophilia (>80% of the patients) with acute infections
  • anaemia and thrombocytopenia - in chronic and advanced disease
  • increased prothrombin time is indicated by an increased INR - may be seen in chronic and advanced disease
  • hypoalbuminaemia
  • raised concentrations of urea and creatinine
  • hypergammaglobulinaemia and hypoalbuminaemia - in chronic and advanced disease (1,2)

Radiology

• chest radiography
  • pulmonary infiltrates can be seen in acute cases (Katayama syndrome)
• abdominal ultrasound
  • can establish extent of liver and spleen pathology in intestinal schistosomiasis
• pelvic ultrasound
  • useful in urinary schistosomiasis to identify the extent of bladder, ureteral and renal pathology (1,2)

Additional investigations:

• cystoscopy - reveals characteristic "sandy patches" (1)
• abdominal X-ray - bladder calcification
• intravenous urogram - may demonstrate hydro-ureter, hydronephrosis or filling defects in the bladder

Reference:

• (1) Gray DJ et al. Diagnosis and management of schistosomiasis. BMJ. 2011;342:d2651.
• (2) Colley DG et al. Human schistosomiasis. Lancet. 2014;383(9936):2253-64.