Diagnosis Of Viral Infections

Question 1

What is the purpose of a laboratory diagnostic test?

Answer 1

Reduce need for unnecessary tests and inappropriate antibiotics
Public health implications
Natural history of the pathogen to treat

Question 2

What are the test types used in viral diagnostics?

Answer 2

Electron microscopy
Virus isolation
Antigen detection
Antibody detection by serology
Nucleic acid amplification tests (NAATs)
Sequencing for genotype and detection of antiviral resistance
Immunochomatographic methods

Question 3

When is electron microscopy used?

Answer 3

Only in characterising new pathogen

Question 4

What are the advantages of using electron microscopy?

Answer 4

Rapid
Detects viruses that cannot culture
Visualisation of viruses

Question 5

What are the limitations of electron microscopy?

Answer 5

Low sensitivity - need 10^6 virons/ml
Requires maintenance
Requires skilled operators
Cannot differentiate between viruses of the same family

Question 6

How does virus isolation work?

Answer 6

Put different cell lines in test tubes or plates and then grow them

Question 7

Why would you do a cell culture?

Answer 7

Check for cytopathic effects of an antiviral

Different cell lines supporting growth of a different virus

Question 8

Where can you detect antigens?

Answer 8

In cells or free in blood, saliva or other tissues

Question 9

What can you detect in nasopharyngeal aspirates?

Answer 9

Cell associated virus antigens of:
RSV
Influenza

Question 10

What can you detect in blood?

Answer 10

Free antigens or whole virus of:
Hep B
Dengue

Question 11

What can you detect in vesicle fluid?

Answer 11

Whole virus of:
Herpes simplex
Varicella zoster

Question 12

What can you detect in the faeces?

Answer 12

Whole virus of:
Rotavirus
Adenovirus

Question 13

When do you use antibody detection by serology?

Answer 13

If the organism doesn’t like culture

Question 14

What can serology be used to do?

Answer 14

Detect an antibody response in symptomatic patients

Check if vaccination has been successful

Question 15

What are the different methods of antibody detection by serology?

Answer 15

Direct immunofluorescence

ELISA

Question 16

How do you carry out direct immunofluorescence?

Answer 16

Antigen bound to slide
Specific antibody to antigen is tagged to fluorochrome and mixed with the sample
Viewed using a microscope equipped with a UV light

Question 17

What are the three formats of an ELISA?

Answer 17

Indirect
Direct
Sandwich

Question 18

When are immunochomatographic methods used?

Answer 18

At point of care for rapid diagnosis

Question 19

What is the method of NAATs?

Answer 19

Specimen collection
Extraction of nucleic acid
DNA transcription for RNA viruses
Cycles of amplification of DNA polymerase
Detection of amplicons

Question 20

What are the advantages of NAATs?

Answer 20

May be automated
Highly sensitive and specific
Generates huge number of amplicons
Rapid
Useful for detecting viruses to make a diagnosis and monitoring treatment response

Question 21

What are the limitations of using NAATs?

Answer 21

Generates large numbers of amplicons (possibly causing contamination)
Need to have an idea of what you’re looking for
Mutations in target sequence may lead to dropout

Question 22

What is multiplex PCR?

Answer 22

When more than one pair of primers is used in the PCR

Question 23

What are the viral enzyme targets in antiviral resistance testing?

Answer 23

Reverse transcriptase, protease
Integrase
Viral receptor binding proteins

Question 24

What is serum produced from?

Answer 24

Processing blood

Question 25

What does serum contain?

Answer 25

Proteins, 
antigens, 
antibodies, 
drugs, 
electrolytes