Schistosomiasis other diagnostic studies

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] ; Associate Editor(s)-in-Chief: Aditya Ganti M.B.B.S. [2]

There are several other methods that can be used in the diagnosis of schistosomiasis such as formalin-ethyl acetate sedimentation, urine testing for schistososme eggs, schistosomal antigen testing, serologic testing, tissue biopsy, PCR etc.

Formalin-ethyl acetate sedimentation

• Five grammes of stool is mixed, strained, diluted with normal saline solution and centrifuged.
• The sediment is collected and treated with formalin-ethyl acetate and subsequently used for slide preparation.
• A single formalin-ethyl acetate sedimentation test is not as sensitive for detection of low-intensity infection as multiple Kato-Katz smears.

Urine testing for schistosome eggs

• The classic method used for identification of S.haematobium eggs is filter concentration of a urine sample collected over 4 hours (ending around noon) into a jug with formalin preservative.
• 10 mL of urine is filtered through a 12-μm pore membrane that traps the eggs, and the membrane surface then is examined under a microscope.
• Standard microscopic urinalysis will not identify low-intensity Schistosoma infections.
• Each separate microscopic urinalysis has a sensitivity of 55% to 62% for detection of low-intensity infection; therefore, at least three different urine samples need to be evaluated to achieve diagnostic accuracy.

Schistosomal antigen testing (urine or serum)

• Urine sample is taken for measurement of circulating cathodic antigen released by schistosomes or serum sample for measurement of both circulating cathodic and anodic antigen.^[1]
• Identifies active infection rather than past infection.
• May not be sufficiently sensitive for detection of low-intensity infection.

Serologic testing

• Serologic testing help in detection of Schistosoma-specific antibodies in serum. These tests include:
  • Enzyme-linked immunosorbent assay
  • Indirect hemagglutination assay
  • Indirect immunofluorescent antibody testing
• More useful for evaluating recent travelers than immigrants, as it is not possible to distinguish between active infection and past infection.
• Due to the long life of schistosomes, positive test results cannot be discounted simply because exposure was historically distant.
• Sensitivity is highest when the assay is targeted to the suspected species (S.mansoni, S.japonicum, or S.haematobium)

Biopsy of tissue

• A biopsy specimen is obtained from the rectum during anoscopy, genital tissues, or the urinary bladder wall during cystoscopy and then crushed and examined under a microscope
• S.mansoni and S.japonicum eggs can be identified in crushed random rectal biopsy specimens.
• S.haematobium eggs can be identified in crushed biopsy specimens from genital tissues or the urinary bladder wall.
• Sensitivity of microscopic analysis of six crushed rectal biopsies is similar to that of two Kato-Katz thick smears.
• Liver biopsy is notoriously insensitive for diagnosis of schistosomiasis; a negative liver biopsy result does not exclude infection.
• Standard sectioned intestinal biopsies are not sufficiently sensitive for diagnosis of intestinal schistosomiasis.

PCR to detect schistosomal DNA

• Gene amplification technique used to detect schistosomal DNA.