Lecture 7 2/7/24 Flashcards
What are the two main ways of diagnosing an infectious disease?
-detection of agent or its components
-detection of antibodies elicited by an agent
What is sensitivity?
proportion of patients with the disease that test positive; true positives
What is specificity?
proportion of patients without the disease that test negative; true negatives
What is positive predictive value?
proportion of patients testing positive that have the disease
What is the negative predictive value?
proportion of patients testing negative that do not have the disease
What is robustness?
test’s capacity to be unaffected by minor variations in test conditions
What are the characteristics of spIN?
-if a test is highly SPECIFIC, trust the POS result
-used to rule a disease IN
What are the characteristics of snOUT?
if a test is highly SENSITIVE, trust the NEG result
-used to rule a disease OUT
Which type of test is good for screening?
sensitive
Which type of test is good for confirmation?
specific
What are the important factors involved in sampling?
-location specimen is collected from
-timing of collection
-proper transport/storage
What are some examples of send-out tests?
-PCR
-sequencing
-FA
-serum neutralization
-virus isolation/ID
-agar gel immunodiffusion
What are examples of send-out or in-house tests?
virology and serology testing
What is a direct test?
test that looks for the virus directly by identifying protein, nucleic acid, or live virus
What is an indirect test?
test that looks for the virus indirectly by identifying antibody responses
What are the characteristics of virus morphology?
-done with electron microscopy
-can provide overall size and shape
What are the characteristics of virus isolation?
-uses primary or continuous cell lines in tissue culture
-need to be aware of how virus might grow in different cell lines and how to visualize the different patterns
What are the characteristics of viral nucleic acid detection?
-always looking for viral presence
-high sensitivity, with ability to detect past infections
-often done via PCR
What are the characteristics of viral enzymatic activity tests?
-looking for activity of viral enzymes
-often done at regulated labs only
-example is hemagglutination assay
What are the characteristics of a hemagglutination assay?
-done with influenza
-hemagglutinin proteins on viral surface bind sialic acid
-RBCs are loaded with sialic acid, thus can titrate out virus and let it react with blood
What is the main thing to know about a hemagglutination inhibition assay?
example of indirect test
What are the characteristics of immunostaining?
-less sensitive than PCR
-indicator that pathogen is present/active within host
-fix antibodies tagged with fluorophore or enzyme to specimen
How does direct vs indirect immunostaining work?
direct: antibody already conjugated to antigen for easy detection
indirect: secondary conjugated detection antibody that reacts with host antibody is needed
What is a direct ELISA?
-wells are coated with patient sample, which acts as antigen
-primary antibody with substrate added for detection of viral antigen
What is an indirect ELISA?
-wells coated with antigen
-antibody from patient serum added with a secondary conjugated antibody for detection of patient antibodies
What type of ELISA is a SANDWICH ELISA?
direct ELISA
Which type of ELISA can be either indirect or direct?
competitive ELISA
What info can be gathered from an ELISA?
-roughly quantified levels
-can tell whether Ab response is effective/protective
-can discern between IgM and IgG
Why are in-house ELISAs more simple?
give a yes/no or +/- result instead of a range that must be interpreted
On a canine 4DX snap test, which disease is tested based on antigen?
heartworm
On a feline FIV/FeLV snap test, which diseases are tested based on antigen?
-FeLV
-heartworm
