Infectious disease testing Flashcards
What are the flaws in antibody testing?
Persistence after elimination of infectious agent
Positive result does ≠ infection
False negative in peracute infections or immunocompromised patients
Generally inferior to antigen testing but not always possible
How does timing of antibody testing affect results?
Aspecific until 8‐12 weeks of age
IgG: only occurs 1‐2 weeks after initial exposure
false negatives before this
repeat test after 2‐3 weeks if still suspicious
What would suggest a recent/ active infection with antibody testing?
‐presence of IgM
‐increasing antibody titer
‐seroconversion
Which antibody assays test for all Ig classes?
Complement fixation
Hemoagglutination
Serum neutralisation
Agglutination assays
Which antibody assays test for specific Ig classes?
Western Blot Immunoassay
Indirect Immunofluorescent Assay (IFA)
ELISA
In which infectious agents can detection of local production of antibodies within the eye or CNS be used to aid diagnosis?
Rabies
Toxoplasma
Distemper
Feline bartonellosis
What do you rate performance of clinical tests on?
Sensitivity & Specificity are the ability of an assay to detect a positive and negative sample respectively
Positive and Negative predictive values are the ability of an assay result to predict the presence or absence of disease respectively
What common GI pathogen can be difficult to detect on faecal flotation
Giardia
What is the best test for the following
Aelurostrongylus Abstrusus
Angiostrongylus Vasorum
Filaroides Hirthi
Baerman
What is the best test for Crenosoma vulpis
Zinc sulphate or other flotations
Which bacteria are most likely to be resistant?
Pseudomonas aeruginosa, Escherichia coli,
Klebsiella pneumoniae, Enterobacter spp,
Enterococcus spp, Staphylococcus
pseudintermedius.
What is the 90/60 rule
90% of simple infections with a non resistant organism will respond to appropriate AB tx
60% of resistant infections will respond
What are the pitfalls of AB sensitivity testing?
They underestimate activity at concentration
What kind of test is the AGAR DISK DIFFUSION TEST
Qualitative
What is the Microdilution Test for Determination of MIC
The lower the MIC value, the more susceptible the isolate is to that drug
MIC50 = inhibits 50% bacteria
What types of molecular diagnostic assay are there?
- Polymerase chain reaction (PCR)
- Quantitative (qPCR) or real‐time PCR
- Reverse‐transcription PCR (RT‐PCR)
- Duplex and multiplex PCR or real‐time PCR
- DNA sequencing
How is FIV diagnosed?
Antibody detection by ELISA
ELISA negative may be PCR positive
Confirm false positive ELISA by Western Blot immunoassay
Prolonged false positivity in kittens
RT‐PCR not accurate to distinguish vaccination
Outline respiratory infectious disease testing
B. Bronchiseptica Culture preferable - Low PPV in cats
Chlamydophila felis – Culture difficult, PCR low PPV, useful post‐infection in catteries
Mycoplasma spp – Culture difficult, PCR low PPV, not useful post‐therapy
FCV & FHV‐1 – also detects vaccinal strains
What are the options for fungal diagnosis?
Cytology - High specificity, variable sensitivity
Histopathology - similar use to cytology
Culture
Serology
IHC - needed to visualise infection in lots of cases
PCR - high specificity but false +ves and -ves common
