Diagnosis Flashcards
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 communtiy risk
Risk group 4
High individual and community risk
BSL-4
Maximum containment laboratory
Handle dangerous and exotic pathogens belonging to highest risk group
Ebola
Biohazard
Biological substances that pose a threat to the health of living organisms, primarily that of humans
Biosafty
Laboratory biosafety describes the containment principles, technologies, and practices that are implemented to prevent the unintentional exposure to pathogens and toxins or their accidental release
Aerosol
V small droplets of fluid that can spread via air
Viruses can spread in lab through aerosol route
Biosecurity
Laboratory biosecurity describes protection, control, accountability for valuable biological materials within laboratories, in order to prevent their unauthorized access, loss, theft, misuse, diversion or intentional release
For virus isolation
Specimens should be collected as soon after onset of symptoms as possible because maximal amounts (titers) of virus are usually present at onset of signs
Chance of viral recovery is best during the first 3 days after onset and is greatly reduced beyond 5 days with many viruses
For serological tests
Two blood specimens are generally collected
One during acute phase of illness
second during convalescence period
Varies upon type of virus, 10-14 days after 1st sample or even more
As a general rule, specimens collected for molecular diagnostics, such as PCR, should be obtained during the early part of the illness
Transport and storage of sample
Viral transport medium- swabs
Prevent spillage, follow basic triple packaging system while transporting infectious materials
Diagnosis of viral infections by gross evaluation and histopatholgy
CS
Necropsy
Histopathology
Detection of viruses by cultivation/isolation
Cultivation/isolation of viruses in cells/tissue culture
Inoculation in eggs
Electron microscopy
Can be used to demonstrate viruses in samples and detect viruses that cannot be grown in vitro
TEM
Method used in TEM based on transmitted electrons
TEM seeks to see what is inside or beyond the surface
Advantages over SEM:
-can produce images that have higher magnification and greater resolution
SEM
Method used in SEM based on scattered electrons
Focuses on sample’s surface and its composition
Advantages over TEM:
- produce 3D images
Gold standard test
A diagnostic test that is considered to be the most accurate and best available under a particular condition or set of condtions
Sensitivity
The probability (%) that cases with the infection (determined by result of the reference or gold standard test) will have a positive result using the test under evaluation
Specificity
Probability (%) that cases without the infection (determined by the result of reference or gold standard test) will have a negative result using the test under evaluation
Collection of serum
Red top vacutainer tube
Collection of plasma
Lavender top EDTA vautainer tube
Plasma produced when whole blood is collected in tubes that are treated with an anticoagulant. Blood does not clot in plasma tube
typical ELISA
Antigen coated in well Add antibody tagged with enzyme Antigen binds to enzyme-tagged antibody Wash the excess unbound antibodies Add substrate Enzyme tagged to antibody which is bound to antigen will change color of substrate. Intensity of color indicated more positive reaction
Direct ELISA
Antigens are immobilized and enzyme conjugated primary antibodies used to detect or quantity antigen concentration
Specificity of primary antibody is v important
Indirect ELISA
Primary antibodies are not labeled, but detected instead with enzyme-conjugated secondary antibodies that recognize the primary antibodies
Sandwich ELISA
The antigen to be measured is bound between layer of capture antibodies and a layer of detection antibodies. The two antibodies must be very critically chosen to prevent cross-reactivity or competition of binding sites
Competative ELISA
A decrease in signal when compared to assay well with purified antigen alone indicates the presence of antigens in the sample
Weaker signal indicates presence of antigens in the sample- positive result
Florescence antibody test- Direct
Labelled antibodies are added onto the sample (Antigen).
Visible fluorescence appears at the binding sites of the specific antibodies (antigen-antibody binding)
Florescence antibody test- Indirect
Employs a secondary antibody labeled with a fluorescent marker that recognizes the primary antibody bound to antigen
Immunohistochemistry
The antibody tagged with an enzyme, generally horseradish peroxidase
The 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)
A form of point-of-care test that is simple to perform, easy to carry, and does not require specialized equipment
like a pregnancy test
Agglutination
Method using the property of specific antibodies to bind many antigens (antigens on pathogen, or antigen coated particles- latex beads) into single clumps thereby forming large complexes, which are easily precipitated
The precipitation can be macroscopically or microscopically visible
Hemagglutination and hemagglutination inhibition test
Relies on the property of some pathogens (mainly viruses) to nonspecifically agglutinate erythrocytes
Agar gel immunodiffusion test
Ag and Ab places in separate wells of agar
Diffuse toward each other
Thin white line formed due to precipitation of antigen/antibody complex
Complement fixation test
Serum from patient A has antibodies against virus A- intact sheep RBCs settle at bottom= positive rxn
Serum from patient B has no antibodies of virus A- find hemolysis of sheep RBC= negative reaction
Neutralization assay
Defined as loss of infectivity through rxn of the virus with specific antibody
