Principles of diagnostic methods
This table gives you an overview on diagnostic targets and the most important methods with their advantages and disadvantages.
| Diagnostic target | Methods of choice | Pros and cons |
| | | |
| Microscopic detection of whole parasites in blood, faeces, urine or tissues (protozoa, helminth ova or larvae) | - A variety of concentration methods and special staining procedures (given later in this chapter)
| - Diagnostic skills and microscopic equipment needed
- Sensitivity not always optimal (need to examine several specimens spaced in time)
- Specificity depends on microscopist
- Methods fail during prepatent helminth infections and if humans are intermediate hosts of cestodes
|
| | | |
Parasitic DNA or RNA
| PCR (Polymerase chain reaction) or nested PCR
- Conventional PCR
- Real-time PCR
- Nucleic Acid Sequence-based Amplification (real-time NASBA)
| - Methods with highest sensitivity and excellent specificity
- Some false negative results due to inhibitors in sample
- Time consuming procedure (except real time PCR and NASBA)
- Investment in equipment and rather expensive reagents
|
| | | |
| Direct detection of Parasite antigens in blood, stool or urine | Immunoassays with mostly specific monoclonal antibodies
- Immuno-enzyme methods (e.g. ELISA)
- Direct fluorescent antibody tests
- Immuno-chromatographic assays (“Rapid diagnostic tests”)
| - High sensitivity
- Detection of active infections
- Efficient testing of many samples
- False negatives due to inhibitory host antibodies
|
| | | |
Immune response against
Parasite antigens
(Detection of antibodies in serum) | Various indirect Immuno-assays using labelled anti-human immunoglobulin conjugates
(e.g. Enzyme-Immunoassays, Indirect Fluorescent Antibody tests, Western blots and others) | - High sensitivity
- Limitations in specificity (due to crude antigen preparations)
- Limitations in sensitivity (when recombinant antigens or synthetic peptides are used)
- Early diagnosis before patent period (helminth infections)
- Persistence of host antibodies after cure
|
