Lab. 4/ class 3 ]MYCOLOGY ASSIST LECT. MAYS JASSIM[

Serological tests for diagnosis of fungi

Fungi culture is often problematic method because its time consuming and insensitive due to low concentration of fungi in specimens.

While Ags and/ or Abs are produced in large quantities and can be found in various body fluid (blood, CSF and urine) also Ags and Abs are easier to detect than finding the organism directly and the results may also be obtained within a few hours without the need of culture before clinical symptoms develop.

So the is a useful tool for rapid diagnosis of fungal disease.

Principle:

 Serological testing is used to diagnosis of some common fungal infections agents including Blastomyces (infect lungs- cause blastomycosis), Histoplasma capsulatum (cause histoplasmosis- acute or chronic lung disease and progressive disseminated histoplasmosis affecting a number of organs.), Coccidioides (infect lungs- Coccidioidomycosis), Aspergillus (infect lungs), and Candida sp. (skin, genital tract and urinary tract infection )

That based on:

1. the patients clinical presentation. 2. their exposure history.

3. risk factor for infection. 4. and target type (Ag/ Ab).

Types of serological targets:

A) For detection of Antigen:

1- Galactomannan (GM-test): it’s highly antigenic a polysaccharide molecule as a components of fungal cell wall found in most of Aspergillus sp., Creptococcus and Candida.

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Figure- 1: Cell wall structure of aspergillus fumigatus

Sample: it can be collected from:

1. Blood: if the aspergillus invades blood it secrets its galactomannan antigen into the blood stream. 2. Bronchoalveolar lavage (BAL): if the fungus found in the airways, asmaal tissue of the infected area is collected by the bronchoscope.

Diagnosis

It can be measured by several commercially technique as ELISA tests and .

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 The result is negative, when the cut off-value is less than 0.5 for serum and equal to 1-2 for BAL. and that indicates to the absence of the fungus.  The result is positive, when the cut off- value is higher than negative result value. And then the fungus is present.

2- B-D- glucan test:

The antigen (1→3)-β-D-Glucan (BDG) is part of the fungal cell wall as an exo- antigen (figure- 1), not specific to any particular species. Its presence in serum indicates the release of the fungal cell wall antigen into the circulation, seen in invasive fungal infections. It may be used in diagnosis of candidiasis or fusariosis by ELISA test and may be used as complementary test to GM test.

Sample: Detection of BDG concentration in serum is now established as one of the criteria for diagnosis of probable invasive mycoses. The result

 negative when the cut off value is less than 60 pg/ml .  positive when the cut off value is more than 80 pg/ml.

3- CrAg- test: is Cryptococcus polysaccharide antigen, is a type of galactcomannan can be detected in serum and spinal fluid by latex (LA) or by lateral flow .

B) :

Antibodies formed against fungal infections can only be detected in EIA, ID and CFT. The high level of antibodies doesn’t prove the presence of disease; due to the presence of anti- fungal antibodies in healthy individuals.

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The main antibodies can be formed in fungal infections as Aspergillosis is IgE and can be detect by RAST and IgG can be detected by ID.

So the available tests to detect of serological targets:

Antibodies:

tests  Radioallergosorbent test (RAST).

Antigens:

 Latex Agglutination.  (RIA).

Antigen and Antibodies

 Complement fixation test  ELISA  Enzyme immunoassay (EIA)

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