Diagnosis of viral infections Flashcards
(28 cards)
Risk group 1
no or low individual and community risk
risk group 2
moderate individual risk, low community risk
risk group 3
high individual risk, low community risk
-pathogen causes serious disease but is not spread often, treatment is available
risk group 4
high individual risk and high community risk
-pathogen causes disease and can be easily transmitted, no treatment available
BSL 4
maximum containment lab, handle dangerous pathogens EX ebola virus
has neagtive air pressure that is contained, HEPA filter for air, steralization through double autoclaving door, decontamination shower
biohazard
biosafety
aerosol
biosecurity
substances that pose a threat to health
protocols to prevent external contamination
very small droplets of fluids that can spread via air
protection, control and accountability for valuable biological materials to prevent loss, theft, etc.
timing of sample collection:
virus isolation vs. serological test
general rule for morphological diagnostic
virus isolation: collect sample as soon as symptoms start, chance of viral recovery is best during first 3 days and declines after 5 days
serological test: collect 2 blood specimens, one during acute phase and one during convalescence period
morph. diagnostic: for PCR, obtain during early part of illness
transporting sample
put swabs into viral transport medium and use triple packing system
diagnosis of viral infection (3 ways)
clinical signs, necropsy, histopathology
detection of virus by cultivation (2 ways)
in cell culture and inoculation in eggs
diagnosis method - EM
- electron microscopy: see characteristic morph.
use negative stain EM, bombard with electron beam, the stain absorbs electrons in much higher amounts than the sample, parts of the viral particles that are not penetrated appear as electron lucent (low affinity, less density), areas on opaque background, to detect: matrix must have 10^6 - 10^7 virions per mL
2 types of EM
- scanning EM: to see surface and topography, scattered electrons, produces 3D images but lower magnification and resolution compared to TEM
- transmission EM: based on transmitted electrons, to see through virus and beyond surface, higher magnification and greater resolution but produces 2D images
assay
gold standard test
qualitative or quantitative measurement of a target entity/analyte such as a drug or biomolecule
diagnostic test that is considered to be the most accurate and best available under a particular condition or set of condition
sensitivity
specificity
probability of cases with the infection that will have a positive result using the test under evaluation
probability that cases without the infection will have a negative result using the test under evaluation
collection of serum - what color tube top?
RED top vacutainer tube
collection of plasma - what color tube top?
lavender top EDTA tube (has anti coagulant)
Direct Enzyme linked immunosorbent assay (ELISA)
- AG coated in a well
- add AB tagged with an enzyme
- AG binds to enzyme-AB
- wash excess unbound AB
- add substrate
- enzyme tagged to AB which is bound to AG will change color of substrate
- intensity of color indicates more positive reaction
-AG immobilized and enzyme - conjugated primary AB are used to detect or quantify AG concentration, specificity of primary AB is very important
indirect ELISA
primary AB are not labelled, but detected instead with enzyme conjugated secondary AB that recognize the primary AB
known AG, unknown AB
sandwich ELISA
AG to be measured is bound between a layer of capture AB and a layer of detection AB - the 2 AB must be very critically chosen to prevent cross reactivity or competition of binding sites - 2 AB are known, AG is unknown
Competitive ELISA
decrease in signal when compared to assay wells with AG alone = presence of AG in sample
-WEAKER SIGNAL = PRESENCE OF AG IN SAMPLE = + ve result
fluorescence antibody test (FAT)
direct vs. indirect
direct: labelled AB are added to the sample (AG), visible fluorescence appears at the binding sites of the specific AB
indirect: IFTA employs a secondary AB labelled with a marker that recognizes the primary AB bound to an AG
Immunohistochemistry
AB is tagged with enzyme, generally horseradish peroxidase, enzyme reacts with a substrate to produce a colored product that can be visualized in the infected cells with a standard light microscope
immunochromatography (lateral flow devices)
what does POC mean
form of POC (point of care) test that is simple to perform, easy to carry and does not require specialized equipment
agglutination
method using the property of specific AB to bind many AG (AG on pathogen, or AG coated particles - latex beads) into single clumps thereby forming large complexes, which are easily precipitated, precipitation can be seen macroscopically or microscopically
