Virology Flashcards
(40 cards)
what features can we detect in suspected viral infection
- infectious virus itself (by isolation or electron microscopy)
- protein components (antigens)
- genetic components (RNA or DNA)
- host response (antibody or cellular response)
what are the main methods of diagnosing viral infections?
o Cell culture and electron microscopy (replaced by PCR)
o Antibody detection – serology (EIA = Enzyme Immunoassay).
o PCR – Polymerase chain reaction detects specific sequences of DNA (genome detection)
o Antigen detection – serology (EIA, IF = Immunofluorescence).
o Quantification of antibody or antigen.
o Serotyping – i.e. in HIV.
o Quantification of genomes – viral load.
o Genome sequencing – genotyping and antiviral resistance testing.
what viruses is genome quantification used for?
diagnosis and monitoring of HIV, HBV, HCV and 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 when investigating viral pathology?
o Throat swab, nasopharyngeal aspirate (NPA), Bronchoalveolar lavage (BAL), ET (Endotracheal tube) secretions for PCR.
o Stools – rotavirus, adenovirus, norovirus for antigen detection (EIA) or PCR.
o Urine – BK virus and adenovirus for PCR.
oCSF – herpes viruses and enteroviruses for PCR.
o Blood (clotted) for serology (antibody detection)
o Blood (EDTA) for PCR / viral load testing.
o Saliva for serology and/or PCR (e.g. measles).
what biochemical markers are looked out for in HIV?
antibody
p24 antigen
what type of antibodies are looked out for in Hep B?
IgM and IgG
what is looked out for in HBV?
surface Ab, Ag, 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 look for in VZV?
IgM
what is IgM a marker of in terms of infection timing?
recent infection
what is IgG a marker of?
as it is created later in host response it lasts longer and indicated an earlier infection
when are IgM and IgG created?
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 the 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 can confirm a positive IgM result?
antibody avidity test
what is avidity?
strength at which antibodies bind to a specific antigen
how does avidity change throughout an infection?
early on it is low but as the ABs mature it increases
avidity= stability of the overall complex of antibody and antigen
what is viral isolation used for despite being time consuming and expensive?
phenotypic antiretroviral susceptibility test
what is immunofluorescence used for?
direct detection of viral antigens
typing and cell culture
rapid and inexpensive but produces subjective results dependent on the skill of the technician
what samples are collected in resp tract infection?
Throat swab, nasopharyngeal aspirate (NPA) Bronchoalveolar lavage (BAL), ET (Endotracheal tube)
then do multiplex PCR with multiple viruses in one tube
what is tested for CNS disease?
- Meningitis or encephalitis – HSV, VZV and enterovirus.
- Young child with febrile fits – Add HHV-6 + parechovirus.
- Immunocompromised (HIV) – Add CMV, EBV, JC virus.
- Recent exotic travel – Japanese encephalitis, West Nile virus, equine encephalitides, tick borne encephalitis.
- Outbreaks – mumps.
