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Body defences: 13. Tests and methods for detecting diseases in humans or other animal organisms - help in diagnosis

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Sub-index of notes: Our body's defence mechanisms against infections from pathogens, help from vaccines & drugs

(13) Tests and methods for detecting diseases in humans or other animal organisms

See also Plant diseases and defences against pathogens and pests


Often symptoms of some disease/infection are quite plain to see in us humans and other animals e.g.

we experience a higher than normal temperature due to some fever condition, a headache or a spotty rash.

But, what you see, feel or measure with a thermometer, might not be enough to properly identify the infection causing the disease.

And, particular problems arise if ...

(i) the symptoms are common to several diseases,

(ii) or the symptoms are uncommon.

Therefore it is sometimes necessary to turn to laboratory analysis of some kind e.g. blood tests or tissue cell tests.

Laboratory techniques

Samples of body fluids e.g. blood, faeces or tissue from the diseased organism can obtained and visually examined or analysed in various ways e.g.

(a) Blood counts

The relative numbers of red blood cells or white blood cells can be important symptoms and help diagnose medical conditions.

A complete blood count is a blood test used to evaluate your overall health and detect a wide range of disorders, including anaemia, infection and leukemia.

If any of the measured concentration of red blood cells, white blood cells (of the immune system) and platelets is abnormal, further investigation would be requires.

(b) Urine analysis

Urine analysis can detect urinal infections, kidney or liver disease and diabetes (the latter is indicated by too much glucose in urine - you can actually do a simple dip stick test).

(c) Detailed visual microscopic examination of cells

Certain diseases can be detected by examining tissue cells under an optical microscope to look for abnormalities.

Cells of abnormal shape indicate the presence of some disease.

Microorganisms such as bacteria can detected and identified by their appearance.

You can stain the samples on the microscope slide to help show up clearer any specific cell or tissue abnormalities or pathogens - the dye can latch onto and become concentrated on particular structures.

(d) Reproducing the pathogen for a more detailed analysis

If the pathogen sample is too small, it can be added to a growth medium to multiply and give a better sample to analyse - either microscopic examination for identification or from DNA analysis (see below).

See Culturing microorganisms like bacteria for more details of the aseptic techniques - to avoid contamination by other microorganisms, therefore avoid identifying the wrong pathogen.

You can also test the pathogen with a selection of antimicrobial compounds to see what kills it - this can help identify the pathogen and what treatment is most likely to be the most effective treatment.

(e) Genetic analysis - DNA sequencing

The isolated suspect microorganism sample can be subjected to DNA analysis.

The genetic profile can be matched against a database of pathogen genomes.

Laboratory tests can identify a specific pathogen by adding sections of DNA known to be complementary to the pathogens DNA.

If the added DNA strands bind to the pathogen's DNA, it means that specific pathogen is present, thereby allowing identification.


See also Plant diseases and defences against pathogens and pests

Learning objectives for this section on detecting and testing for pathogens

Know some test methods for detecting diseases to help in diagnosis of human conditions e.g. blood counts, urine analysis, microscopic examination of cells and DNA sequencing of samples of the pathogen.



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