WEEK 11: 11.9 Diagnostic Virology Flashcards
(22 cards)
What are diagnostic methods for viral infection used for?
It is used by research and pathology labs, to determine cause, stage, treatment and epidemiology of a viral disease, and effectiveness of vaccines
What factors do the samples we collect/diagnostic tests we run depend on?
1) clinical presentation : site of the virus infection and release
2) risk factors (travel)
3) test type: detection and/or isolation of causative agent
4) diagnostic test we choose: depends on whether we are testing for current (virus particles and/or viral genomes/proteins) or previous (serology/antibody response) infections
What is the method for sampling if the virus is localised in the enteric GI tract? eg. poliovirus, norovirus, rotavirus
faeces/vomit- viral particles/genomes/proteins
blood- serum antibodies
What is the method for sampling if the virus is localised in the respiratory tract ?
nasal swab- viral particles/genomes/proteins
blood - serum antibodies
What is the method for sampling if the viral is blood-borne?
liver biopsy sample (blood sample) - viral particles
blood - serum antibodies
what is the method for sampling is the virus is localised STD blood borne
blood - serum antibodies
heparinised - levels of CD4 T cells
What needs to be considered in the transportation of specimens collected
It is criticle to maintain a viable virus, so the virus does not become inactivated and hence the genome and antigens must be intact with the virus.
What temperature and tools help maintain a viable virus?
appropriate temp using dry ice/liquid nitrogen
either completely freeze at -80 degrees or keep cold at 4 degrees.
collection kits provide an external environment conducive to viral life
describe the diagnostic method for virus infection
- grow virus in vitro in cell lines and identify; observe cells for cytopathic effects
- look directly for virus using electron microscopy
- detect virus proteins (antigens); detection relies upon the availability of antigen specific Abs
- detect genome (RNA/DNA) by RT-PCR or PCR
- detect antibodies in serum of infected patients
We need viable viruses to allow?
- Isolation in ‘Cell culture’
- Confirm diagnosis
- Allow cytopathic effects
What temperature in virus storage should be avoided
freeze to -20 degrees- can create ice crystals
What type of virus is more adversely affected by storage conditions like temperature?
enveloped viruses
What are the requirements for the cell line?
they are innoculated with the specimen
they must have a proper receptor for virus attachment and entry into cell
What are the different types of cell lines used?
HEL
MDCK
VERO
BGM
What two types of antigen testing can we use?
Immunostaining/immunofluorescence- detect single positive cell, requirement for intact cells, labor intensive
Rapid antigen tests - detect the presence of antigen but need to consider the quality and quantity of antigen
What do rapid antigen tests do?
they look for the presence of protein antigens
How does the RAT test work?
the sample is exposed to paper strips containing antibodies designed to bind to antigens,
antigens bind to the strips, diffuse and give a visual readout
Describe the benefits and drawbacks of RAT
fast
deliver results at point of care
limited accuracy (80%)
does not require expensive equipment
What does a PCR do (polymerase chain reaction)
it analyses genome sequence of virus
What are the two types of PCR
RT- PCR (RNA viruses)
Quantitative PCR (DNA viruses)
What is the process of detecting antibodies in serum of infected patients called?
A serological diagnosis
