Virology Flashcards
What are the two major ways we can detect viruses?
Host antibodies
Antigen
When testing for antigens in a sample, what specifically might we be looking for?
Viral proteins
Nucleic acids
Live virus
ELISAs, lateral flow assay, agar gel immunodeficiency are examples of….
Antibody detection tests
In very simple words, how does an antibody detection test work?
Test has antigen
Patient antibodies react with test antigen
Reaction visualized (or quantified - titer)
What is the goal of viral isolation?
Grow virus from diagnostic sample and identify
__________ is gold standard for virus detection
Viral isolation
Only test to prove viable virus
What other additional things can we use viral isolation for?
Cytopathic effects
Electron microscopy
Fluorescent antibody testing
Hemagglutination/hemagglutination inhibition
PCR
Sequencing
What cytopathic effects do we see with pox virus?
Swollen cells, cytoplasmic inclusions
What cytopathic effects do we see with herpes virus?
Cytoplasmic stranding, nuclear inclusion
Pros to viral isolation
Detect living virus
Can detect and identify unknown viruses
Sensitive
Can amplify and collect live virus for research
Cons to viral isolation
Requires special cell lines and training
Wait time
$$$
Sensitive to contamination
Capture or sandwich assay are types of ______
ELISA
How does fluorescent antibody testing work?
Direct method identifies presence of antigen in tissue
Fluorescent labeled antibodies bind target antigens
How does lateral flow assays work?
Labeled antibodies or antigen conjugate present on platform
Sample containing antigen or antibody added
Positive samples will bind to either antigen or antibody on plate
Pros to lateral flow assays
Quick
Minimal equipment
Less expensive
Some done in clinic
Cons to lateral flow assays
Less specific
Risk of false positives
Not as likely to be accepted for regulatory purposes
Cross reactivity
Give an example of a lateral flow assay used in practice
Parvo (antigen)
FIV (antibody)
BVD is commonly tested for using an ______
ELISA
What is a good example of when FA are used?
Rabies
PCR =
Polymerase Chain Reaction
What is real-time PCR?
Quantifies viral load
What type of PCR do we use for RNA virus detection?
Reverse transcriptase PCR
Sequencing is another method of detecting nucleic acids. You can either sequence a ________ or the ________ genome
Partial or full
Pros to PCR
Fast
Sensitive
Reliable
Cons to PCR
No distinction between live vs inactive
Can only detect known viruses
May miss if mutated
Contamination can be an issue
Respiratory, abortion, and enteric panels are examples of
PCR testing
T/F: Wooden handles and calcium alginate are preferred materials used for PCR sample collection
False - inactivate virus and interfere with PCR
What kind of swabs are safe for PCR?
Synthetic:
Polyester
Dacron
Nylon
Rayon
Flocked = catch more virus
T/F: You should always mix samples for laboratory submission to cut down on shipping costs.
False - don’t pool tissues and never mix GI samples with other samples
What are some characteristics of a virus?
DNA or RNA based
Infect animals, plants, bacteria, fungi
CS often vague
Few treatment options
Often have prevention options
Why is viral detection important?
Prevent introduction
Target care
Limit spread
Lateral flow assays are commonly known as _____ tests in clinic
SNAP
When using an antibody test, what must you take into account?
Lag time from infection
T/F: antibody tests are the ideal tests to use in an outbreak
False - you will always be behind the infection if you are using antibody tests in an outbreaks d/t the lag time from infection
What kind of ELISA am I describing?
Plate with antigen, patient serum added to plate, enzyme binds to antibody if present
Direct ELISA
How does an indirect ELISA differ from a direct ELISA?
Instead of adding just an enzyme to the plate to bind the antibody, you will be adding a secondary antibody that has the enzyme bound to it
T/F: when running a competitive ELISA, less of a reaction means more antibody is present
True - this is due to the inhibitor antigen that is present on the plate
How can you get a titer from an ELISA?
Presence of color in the well = positive
If you dilute the sample across multiple wells, the last well with color present is the highest tighter (inverse of dilution)
What is agar gel immunodiffusion most commonly used for?
Coggins - EIA
Explain how an agar gel immunodiffusion test works
Antigen in center
Samples and controls around edges
Positives will form a reactive, precipitate line around the center well
How does a hemagglutination inhibition test work?
Typically, blood will clot if left in a well
Certain viruses bind the surface of the RBC and don’t allow clot formation leading to a flat layer along the well
For inhibition test, we add RBCs, virus, and patient serum to see if the antibodies bind the virus, allowing the RBCs to clot
T/F: In a plate agglutination test, patient sample is added to a plate with antigen. If patient is negative, clumps will form.
False - clumping indicates presence of antibody in patient sample binding with antigen on plate
T/F: Lateral flow assays can be used to identify antigen or antibody in a patient sample. It just depends on what conjugate is on the plate.
True
What kind of tissue is used for IHC?
Fixed
What does IHC show?
Exposes antigen
IHC can be used for…
FIP and Marek’s
Pros of AGID and HIs
Specific
Gold standard for some tests
Often accepted for import/export
Cons of AGID and HIs
Harder to find
Longer incubation
Labor intensive
Often more expensive
Pros to FAs and IHCs
Specific
FAs - fast, visualize pathogen location
IHCs - option for fixed tissue, visualize pathogen location
Cons to FAs and IHCs
Rarely antemortem
Can be expensive
May be species specific
Limited assays
Detecting current infection and immunotolerant animals is a benefit of _________ testing
Antigen
Detecting previous/chronic infection or detecting vaccination that elicits IgG are benefits of ___________ tests
Antibody
T/F: the lower the CT value, the more pathogen present
True
Pros to sequencing
Large amount of data (great for epidemiology)
ID unknown pathogens
Track mutations
Cons to sequencing
Expensive
Lots of analysis
Best on pure sample
Virus can be cultured using ________ and ________
Embryos and special cell lines
What are some common cell lines?
Embryonic or adult
Kidney
Liver
Rounding of cells, syncytia, plaques, vacuoles, and inclusion bodies are all types of _________
Cytopathic effects
What type of stain is crucial in order to utilize electron microscopy?
Heavy metal salts
Viral inclusions are usually ___________
Pathognomonic
T/F: You can rule out the presence of a virus based on lack of inclusion bodies on histopathology
False - May only be present in one stage of infection or may not be in the sections taken
A client wants to prove the absence of avian influenza virus on their farm following an outbreak. What is the best test to choose?
Viral isolation! Only test that shows presence of viable virus
RT-PCR drawback would be detection of inactivated and live virus - may make client wait longer
What is the difficulty when trying to diagnose FIP?
A lot of tests will test for FCoV, not the mutated virus that causes FIP
Does a FCoV negative ELISA mean this cat does not have FIP?
No - in late stage FIP, antibodies drop and may not be detected
T/F: the most suggestive test for FIP of all available tests is a fecal PCR
False - positive PCR on abdominal fluid would be the most suggestive, but still not definitive
