Virology [Complete] Flashcards
What features can we detect in suspected viral infection?
Infectious virus (by isolation or electron microscopy)
Protein components (antigens such as p24 antigen in HIV)
Genetic components (RNA or DNA)
Host response (antibody or cellular response)
What are the main methods of diagnosing
Cell culture and electron microscopy (replaced by PCR)
PCR (Polymerase chain reaction): [Detectes genome]
Detects specific sequences of DNA.
Antibody detection:
Serology (EIA = Enzyme Immunoassay).
Antigen detection:
Serology (EIA and IF = Immunofluorescence).
Quantification of antibody or antigen.
Serotyping – i.e. in HIV.
Quantification of genomes – viral load.
Genome sequencing – genotyping and antiviral resistance testing.
what viruses is genome quantification used for?
HIV
HBV
HCV
CMV/EBV
In the immunocompromised.
What are the limitations of lab tests?
False negatives due to sensitivity
False positives due to specificity
What is sensitivity
Ability to correctly identify positive samples
What is specificity
Ability to correctly identify negative samples
What types of samples can be taken and when would they be taken?
For detection of respiratory viruses by IF or PCR:
Throat swab
Nasopharyngeal aspirate (NPA)
Bronchoalveolar lavage (BAL)
ET (Endotracheal tube) secretions for PCR.
Stools: For detection of rotavirus, adenovirus, norovirus for antigen detection (EIA) or PCR.
Urine: BK virus and adenovirus for PCR.
CSF: herpes viruses and enteroviruses for PCR.
Blood: (clotted) for serology (antibody detection)
Blood (EDTA) :for PCR / viral load testing.
Saliva for serology and/or PCR (e.g. measles).
What is the difference between IgM and IgG in terms of when theirlevels rise following infection?
IgM is a marker of RECENT infection
IgG rises later on in the infection and some remains after the infection has passed
What is IgM a marker of?
Recent infection
What is IgG a marker of?
As it is created later in host response it lasts longer and indicates an infection which occured earlier
When are IgM and IgG made and when do they usually peak?
Both created in acute phase of disease.
IgM peaks early and drops off after a few weeks while IgG only get higher and plateau
What is looked out for in HIV
Antibodies
p24 antigen
What is looked out for in Hep B?
IgM and IgG
What is looked out for in HBV
Surface Ag/Ab
eAg/eAb
Core Ab
Core IGM
What is looked for in HCV
Antibody with or without core antigen
What is looked for in CMV,EBV, MMR and parvovirus B19
IgM and IgG
What is looked for in VZV?
IgM
process of HIV serology testing
4th gen: Currently detects antibody and p24 antigen
Positive result goes into confirmatory test to reduce false positives in an assay
Confirmed positives undergo typing for HIV 1 or 2 - samples repeated and EDTA blood for viral load (for genotyping and resistance testing)
What does positive IgG and absent IgM indicate?
Past infection or immunisation
what can confirm a positive IgM result?
Antibody avidity test
What is avidity?
Strength at which antibodies bind to a specific antigen
Describe how antibody avidity changes in infection.
Early on in the infection, avidity is LOW
Then you get maturation of the antibody response so the avidity will increase over a period of 3-6 months
If you have HIGH antibody avidity, then it is unlikely that the infection occurred in the last 3 months
What is viral isolation used for despite being time consuming and expensive
Phenotypic antiretroviral susceptibility test
what is immunofluorescence used for? What are the advantages and disadvantages?
Direct detection of viral antigens typing and cell culture
Advantage: rapid and inexpensive
Disadvantage: produces subjective results dependent on the skill of the technician
