Diagnosing Disease

Question 1

What can be done to make a specific aetiological diagnosis of infection?

Answer 1

Demonstrate the presence of organisms, components and/or products
Isolate an organism
Demonstrate a serological response

Question 2

What are some techniques that can be used to demonstrate the presence of an organism?

Answer 2

Microscopy, antigen detection, nucleic acid detection, biochemical tests, etc

Question 3

What forms of microscopy can be used?

Answer 3

For light microscopy, unstained preparations can be used, especially for parasites. Stained preparations are good for bacteria and electron microscopy is an option for hard to culture viruses (though really only as a last resort)

Question 4

How can you test for the presence of antigens?

Answer 4

First, the antigens must be captured in some way. This can be done by placing it in a solution. Then, latex particles with bound antibodies specific to the antigen of interest can be placed within the solution. Should these antibodies bind antigen, the latex will clump or agglutinate, and the test it positive.
Another option is capturing the antigen on a solid phase. This can be done by directly fixing the sample onto a solid surface, or by coating a surface with antibody and washing the sample over the surface. A labelled antibody is then used to determine whether there is any antigen of interest on the surface.

Question 5

How can the presence of nucleic acids be determined?

Answer 5

Hybridisation with a labelled probe for the sequence of interest, or PCR

Question 6

FINISH 1.10

Answer 6

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