Schistosoma haematobium - Laboratory Diagnosis, Treatment, Prevention, Control

Laboratory diagnosis of Schistosoma haematobium

Diagnosis of Schistosoma haematobium includes cystoscopic examination and digital examination of the rectum- especially in patients of endemic areas presenting macroscopic haematuria.

In a laboratory, diagnosis of schistosomiasis is done by demonstration of typical non-operculate terminal-spined eggs.

Samples

• Urine (most common)

  * Since the proportion of blood fluke eggs is excreted the most between 10 am and 2 pm, urine is collected at that time.

• blood (serum)

• feces (if the intestine is involved)

• rectal biopsy (if the intestine is involved)

• aspirations (from proctoscopy, cystoscopy)

Microscopy

Microscopy of urine samples is the most common method. Following concentration by centrifugation or membrane filtration, the residue is microscopically examined.

If urine collected within 24 hours gives the result of more than 50 eggs per 10ml of urine, infection is determined as severe while those of less than 50 eggs per 10ml of urine is considered as light infection.

Urine microscopy is also done to check for the effectiveness of treatment through egg viability tests. To test the effectiveness, urine is mixed with distilled water and observed for hatching miracidia. If eggs are viable, miracidia hatch rendering the treatment ineffective.

Membrane filtration

• urine (10ml) is passed through a nucleophile membrane filter (13mm diameter with 8μm pre)

• part of the membrane holding residue is microscopically examined at 40x magnification

• presence of terminal spined eggs confirms infection by Schistosoma haematobium

Detection of antibodies

Serodiagnosis methods can be used to demonstrate specific circulating antibodies in the patient's serum. It uses purified schistosome antigens to antigen fractions with specific antigenic determinants.

These tests are mostly used to detect infection during the pre-patent period, chronic infection, and ectopic infection as well as for epidemiological studies.

However, its major disadvantage is its inability to differentiate between active and past infections as antibodies remain in the serum for a long time. Also, these tests cannot quantify egg/infection load.

Schistosoma-specific antibody detection methods include:

• Indirect haemagglutination (IHA)

• Radio Immuno Assay (RIA)

• enzyme-linked immunosorbent assay (ELISA)

• Falcon assay screening test (FAST)-ELISA

  * FAST has high sensitivity (95%) and specificity (99%)

  * uses haematobium adult worm microsomal antigen (HAMA)

• Immunoblot

Detection of antigen

These tests are based on the detection of Schistosoma haematobium antigen in the serum or urine. They also help in the detection of autoinfection and the difference between active and past infections.

The tests include:

• immunoelectrophoresis-in-gel, counter-current immunoelectrophoresis (CIEP)

• enzyme-linked immunosorbent assay (ELISA) – high sensitivity

  * demonstration of proteoglycan gut-associated antigens such as circulating anodic antigen (CAA) and circulating cathodic antigen (CCA)

• Radio Immuno Assay (RIA)

Imaging methods

• X-ray

• Ultrasound

Other tests

• Histological test (bladder biopsy) for urinary schistosomiasis

Treatment of Schistosoma haematobium

Drugs of choice include Praziquantel, and Metrifonate while Nitridazole is no longer used due to its toxicity and carcinogenic properties.

Prevention, Control of Schistosoma haematobium

• immediate treatment of infected people

• use of molluscicides to control snails

• education and awareness

• reduce contamination of water sources by human urine