Lecture 6 - Diagnostic Virology

A viral infection can be confirmed with a variety of lab techniques, what are the 5 broad categories of lab techniques used to confirm a viral infection?

1. Detecting the presence of the virus

2. Detecting viral antigens

3. Detecting viral nucleic acids

4. Detection of specific AB response in host

5. Visualization of the virus

What 3 things are required for the vet to do in order to submit a sample properly?

1. Correct sampling procedure

2. Clinical history of the patient

3. Request a specific test

T/F: How you collect/store the sample for testing depends on the type of virus

True

_____ ______ is thought to be the gold standard of viral detection, however, it is very time consuming and requires varying specific agars/collection methods

Virus Isolation

Viral detection via electron microscopy used to be one of the go-to methods, however it has been replace by…

PCR

Detecting viral nucleic acid is another methods of viral detecting, what are the 3 main benefits of this type of viral detection, what is procedure called?

1. Fast

2. Inexpensive

3. Accurate

Polymerase Chain Reaction (PCR)

How does PCR work?

• It uses primers and polymerases to replicate the isolated nucleic acid

  • The polymerases are activated by temperature

• It continues to replicate for 20-30 cycles, producing around 33 million copies of the original strand of starting material

• After that they use agarose gel and a DNA dye to stain the nucleic acid and product and separate the DNA based on size

• If the expected size of the PCR product matches the DNA of the suspected virus then it is considered to be positive

Are false negatives possible for PCR?

Yes, if the virus has mutated then it wouldn’t match the comparison sample

T/F: Histology can be used to identify and rule out a viral infection?

• False

  • It can’t rule out viral infections

  • While it can detect the presence of a virus, it cannot ID it

Another method of viral detection is using the viral antigen to confirm an infection, how do these tests detect viral antigens?

• They use viral antibodies that are specific for a particular type of virus

• When the virus binds to the antibodies the test then releases a immunofluorace that specifically binds to that antigen and causes coloration, indicating a + test result

  • Examples of this would be a snap test

T/F: detection of antibodies is enough to indicate a current infection

False, while it could be true, ABs can also be present in healthy individuals because of past infections

Can the cause antibodies be distinguished from each other (infection vs vaccination)?

No, both instances will trigger the production of antibodies so this can be a concern if the patient was vaccinated recently, it could cause a false positive