Taylor-Leigh Siebritz
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Serology: Immunoassays
Serology: Immunoassays
The detection of unique parasitic antigens, which are proteins (- complexes, enzymes) are used in immunoassays, with serology. This type of diagnosis is also termed as Immunodetection (Fitri, et al., 2022).
ELISA (Enzyme Linked Immunosorbent Assay):
ELISA (Enzyme Linked Immunosorbent Assay):
Using a commercially available kit, the patient stool sample is added to a fixed antibody within a test tube or container, that is specific for the G. lamblia surface antigen. An enzyme-conjugated substrate is then added to the same container. If the patient sample is positive (i.e. the antigens and antibodies have bound), the enzyme cleaves the substrate, producing a visible colour change (Fitri, et al., 2022).
Figure 24: A commercially available ELISA kit, specific for Giardia parasite detection (Diagnostic Automation (8310-3)).
Immunochromatography (Lateral Flow Testing):
Immunochromatography (Lateral Flow Testing):
Similar to ELISA tests, the Lateral Flow Test detects Giardia surface antigens; this test does not require the addition of a substrate. The Lateral Flow tests are usually used as an alternative method to ELISA, especially in under-facilitated and low-skill staffed regions (Vicente, et al., 2024).
Figure 25: The Lateral Flow Test, specific for Giardia parasite detection (Diagnostic Automation (8310-3))
Direct Fluorescence Antibody (DFA) Tests:
Direct Fluorescence Antibody (DFA) Tests:
Using the dye, fluorescein, to label the antibodies against Giardia lamblia cyst wall antigens and/or trophozoite surface proteins, DFA produces a visualization of the intact parasites, and a definitive diagnosis (Fitri, et al., 2022).
Figure 26: Visualisation with Immunofluorescence Microscopy, after DFA Immunoassay for the (a) anti-acetylated tubulin, and (b) anti-tyrosinated tubulin antibody. The arrows indicate the median body (Gadelhaa, et al., 2019).
Advantages of Immunoassays: (Fitri, et al., 2022)
Advantages of Immunoassays: (Fitri, et al., 2022)
rapid detection
high sensitivity and specificity in giardiasis diagnosis
no live parasites required
simultaneous diagnosis of other intestinal parasites
straight-forward execution
minimised human error
Disadvantages of Immunoassays: (Fitri, et al., 2022)
Disadvantages of Immunoassays: (Fitri, et al., 2022)
expensive, single-use kits
supplementary equipment required, such as an ELISA reader
supplementary skills required, including microscopy and sample preparation
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