Virology Flashcards
what antibodies do we usually test for
usually IgG, but sometimes IgM. IgM takes longer to develop
what is a direct ELISA
antigen on plate and patient antibody binds. an enzyme allows visualization
what is indirect ELISA
antigen on plate. patient antibody binds then a secondary antibody conjugate is added for visualization
what is a competitive ELISA
antigen on plate. patient antibody binds. then an inhibitor antigen binds to decrease color reaction. so, less of a reaction on the plate means more host antibody is present. opposite from other ELISAs
describe titers
using ELISA testing, sample is diluted in a serial manner until no reaction occurs. the last well with a reaction is your titer
what is lateral flow assay
SNAP tests. may test for antigen or antibody
what is agar gel immunodiffusion? examples of its use?
antigen in middle. samples and controls in a circle around it. positive samples will have a white line near it. very reliable. gold standard
ex: coggins
what is a hemagglutination inhibition test
some viruses bind RBCs and prevent agglutination. serum is added and if antibodies are present, they will stop the virus from binding and allow the blood to clot. gold standard
what is a plate agglutination test
mix serum with stained antigen and form clumps if there is antibody. larger clumps with more antibodies
what viral protein is usually tested for
spike proteins
what is a capture/sandwich ELISA
antibody fixed to plate. antigen present in serum binds the antibody. add another label antibody for visualization.
useful for BVD where patient wouldn’t have antibody
what is fluorescent antibody testing? what is it used for?
direct method. fluorescent labeled antibodies bind target antigens in fresh tissue. look under fluorescent microscope.
ex: rabies
what is immunohistochemistry? what is it used for?
like IFA, but use fixed tissue. expose tissue to antibody then visualize under a normal scope. see the effect of virus in tissues, can see viral inclusions in the cell (usually pathopneumonic)
ex: FIP, marek’s dz
what are the pros and cons of ELISAs and lateral flow assays
pro - quick, less expensive, readily available, some done in clinic, can get titers with ELISA
cons - less specific/risk of false positives/negatives (esp with lateral flow), not as likely to be accepted for regulatory purposes, cross reactivity possible
what are the pros and cons of AGID (agar gel immunodiffusion) and HIs (hemoagglutination inhibition)
pros - specific, gold standard for some tests, often accepted for import/export
cons - harder to find, longer incubation, labor intensive, often more expensive
what are the pros and cons of fluorescent antibody tests and immunohistochemistry
pros - both usually quite specific, visualize pathogen location, FA is fast, IHC is an option for fixed tissue
cons - rarely an antemortem test, can be expensive, may be species specific, limits assays
differentiate antigen vs antibody tests
antigen - detect current infection, detects in immunocompetent animals
antibody - detect previous/chronic infection, detects vaccination that elicits IgG
what is the benefit of real-time PCR
it quantifies viral load
what does a higher Ct value mean in PCR
more cycles for the sample to break through the threshold, so less virus present
what is a multiplex panel
PCR panel for multiple viruses that cause similar signs
what is whole genome sequencing
done on a pure viral sample. usually used for epidemiology and research
what is metagenomic sequencing
start with a mixed sample and sequence everything in it. computer helps analyze the data
what are pros and cons for PCR
pros - fast, sensitive, reliable
cons - no distinction btwn live and inactive, may miss if virus mutates, contamination issues, need to know what you’re testing for
what are the pros and cons for sequencing
pro - large amount of data, ID unknown pathogens, track mutations
cons - expensive, lots of analysis, best on pure samples
describe viral isolation
grow virus from diagnostic sample to identify, gold standard, only test to prove viable virus is present
what media are used for viral culture
embryos and special cell lines. cell lines should be similar to tissue the virus infects
how do you know virus is growing on your culture
usually thru cytopathic effects or electron microscopy
can also use fluorescent antibody test, hemagglutination, PCR, sequencing
what is cytopathic effects
damage done by viruses on cells
why might you use virus isolation
with low viral load, unknown pathogens, and for species without serological or molecular tests
describe electron microscopy
stained with heavy metal salts to visualize surface structures, can search blindly, can detect primary and secondary pathogens
T/F: if you don’t see inclusion bodies on a group of cells, there are no viruses present that can cause inclusion bodies
F - usually only present at certain stages of disease
pros and cons of virus isolation
pros - detect living viruses, detect and identify unknown viruses, sensitive, amplify and collect live virus
cons - difficult, long wait time, expensive, sensitive to contamination
pros and cons of electron microscopy
pros - visualize pathogen, work even if mutated, false positives rare, see all actors involved
cons - expensive, less common, longer turnaround time, may pick up an innocent bystander
pros and cons to histopath
pros - false positives unlikely, inclusions often distinct and pathognomonic, virus inactivated so no risk of spread
cons - absence of inclusions ≠ negative, longer turnaround time
what kind of swabs should not be used for viral testing
wood - antiviral, interferes with PCR
calcium alginate - interferes with viral isolation and PCR testing
what kind of swabs pick up more virus
flocked - has bristles
with a case of avian influenza where you are trying to decide if it is safe to bring in new birds, which test should you use to be sure your flock is virus free?
a. lateral flow assay
b. real time PCR
c. virus isolation
c is best. tells if any viable virus present
a- quick, but risk of false positives
b- sensitive, but detects inactivated virus as well as live. would be ok, but would end up waiting longer than necessary to bring in new birds
what test is accepted from the regulatory bodies for avian influenza
virus isolation
how much tissue is needed for viral testing
not a lot. a few grams
what test should be used with a herd of cattle with respiratory illness
PCR resp panel. histology helpful but may not be diagnostic
you have a cat with clinical signs consistent for FIP. a fecal sample is PCR positive for coronavirus. does this cat have FIP?
not necessarily. normal coronavirus and FIP are both shed in the feces
is PCR, fluorescent antibody test, or lateral flow assay helpful in testing for FIP
no, do not differentiate typical coronavirus from 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. serum testing not helpful for FIP
an abdominal fluid sample is PCR positive for coronavirus. does this cat have FIP
not definitive, but is suggestive. good enough to act on this.
histopathology and immunochemistry on biopsy tissues are more definitive than PCR
how should whole fish be sent to the lab
overnight on ice packs or dry ice.
not formalin b/c inactivates virus. not with ground shipping or just an insulated envelope. will rot
