Diagnosing Viral Infections Flashcards
What are the two most important requirements for sampling a site of infection?
TIME- as soon as possible after the onset of clinical signs
SITE- often obvious from clinical signs, site of maximum viral replication e.g. Nasal swabs
What is the benefit to growing a Virus in a lab?
virus is amplified & therefore easier to detect
What are the cons to growing a Virus in a lab? (4)
- Need to have a suspect in mind
- Takes several days (depending on virus)
- Not all viruses can be cultured
- Requires live virus
What happens when we use negative staining for direct visualisation of Virus particles?
the heavy metal stains, stain the background- stain is non permeable for electrons and virus is permeable so shows up
What are the benefits to using electron microscopy for Virus diagnosis? (2)
Can be used for viruses that can’t be cultured & allows identification of new agents
What are the disadvantages to using electron microscopy for Virus diagnosis? (3)
requires specialist equipment & experienced personnel
will identify the family of virus but further information is required for more specific identification
In what ways can we detect viral nucleic acid? (3)
- Hybridisation methods e.g. microarray
- PCR based methods e.g. PCR , reverse transcriptase -PCR, real time or quantitative PCR, digital PCR, etc.
- Viral genomic sequencing and partial sequencing
What are the benefits to using PCR as a diagnostic technique? (3)
- Very sensitive, can use very small amounts of starting material to get amplification of target
- Does not require live virus
- Fast turn around time
What are the cons of using PCR as a diagnostic technique? (3)
- Very sensitive
- Danger of contamination
- False positives
What tests would we use for the detection of serum antibodies? (3)
neutralisation assay, hemagglutination inhibition assay and/ or an antibody ELISA
What are the disadvantages to using serum antibody tests for Virus detection?
a negative test doesn’t always mean no exposure (lag phase in virus growth)
