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