Diagnosis Of Viral Infections Flashcards
What is the purpose of a laboratory diagnostic test?
Reduce need for unnecessary tests and inappropriate antibiotics
Public health implications
Natural history of the pathogen to treat
What are the test types used in viral diagnostics?
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
When is electron microscopy used?
Only in characterising new pathogen
What are the advantages of using electron microscopy?
Rapid
Detects viruses that cannot culture
Visualisation of viruses
What are the limitations of electron microscopy?
Low sensitivity - need 10^6 virons/ml
Requires maintenance
Requires skilled operators
Cannot differentiate between viruses of the same family
How does virus isolation work?
Put different cell lines in test tubes or plates and then grow them
Why would you do a cell culture?
Check for cytopathic effects of an antiviral
Different cell lines supporting growth of a different virus
Where can you detect antigens?
In cells or free in blood, saliva or other tissues
What can you detect in nasopharyngeal aspirates?
Cell associated virus antigens of:
RSV
Influenza
What can you detect in blood?
Free antigens or whole virus of:
Hep B
Dengue
What can you detect in vesicle fluid?
Whole virus of:
Herpes simplex
Varicella zoster
What can you detect in the faeces?
Whole virus of:
Rotavirus
Adenovirus
When do you use antibody detection by serology?
If the organism doesn’t like culture
What can serology be used to do?
Detect an antibody response in symptomatic patients
Check if vaccination has been successful
What are the different methods of antibody detection by serology?
Direct immunofluorescence
ELISA
How do you carry out direct immunofluorescence?
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
What are the three formats of an ELISA?
Indirect
Direct
Sandwich
When are immunochomatographic methods used?
At point of care for rapid diagnosis
What is the method of NAATs?
Specimen collection Extraction of nucleic acid DNA transcription for RNA viruses Cycles of amplification of DNA polymerase Detection of amplicons
What are the advantages of NAATs?
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
What are the limitations of using NAATs?
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
What is multiplex PCR?
When more than one pair of primers is used in the PCR
What are the viral enzyme targets in antiviral resistance testing?
Reverse transcriptase, protease
Integrase
Viral receptor binding proteins
What is serum produced from?
Processing blood
What does serum contain?
Proteins, antigens, antibodies, drugs, electrolytes
