Infectious disease testing

Question 1

What are the flaws in antibody testing?

Answer 1

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

Question 2

How does timing of antibody testing affect results?

Answer 2

 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

Question 3

What would suggest a recent/ active infection with antibody testing?

Answer 3

‐presence of IgM
‐increasing antibody titer
‐seroconversion

Question 4

Which antibody assays test for all Ig classes?

Answer 4

 Complement fixation
 Hemoagglutination
 Serum neutralisation
 Agglutination assays

Question 5

Which antibody assays test for specific Ig classes?

Answer 5

Western Blot Immunoassay
Indirect Immunofluorescent Assay (IFA)
ELISA

Question 6

In which infectious agents can detection of local production of antibodies within the eye or CNS be used to aid diagnosis?

Answer 6

Rabies
Toxoplasma
Distemper
Feline bartonellosis

Question 7

What do you rate performance of clinical tests on?

Answer 7

 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

Question 8

What common GI pathogen can be difficult to detect on faecal flotation

Answer 8

Giardia

Question 9

What is the best test for the following

Aelurostrongylus Abstrusus
Angiostrongylus Vasorum
Filaroides Hirthi

Answer 9

Baerman

Question 10

What is the best test for Crenosoma vulpis

Answer 10

Zinc sulphate or other flotations

Question 11

Which bacteria are most likely to be resistant?

Answer 11

Pseudomonas aeruginosa, Escherichia coli,
Klebsiella pneumoniae, Enterobacter spp,
Enterococcus spp, Staphylococcus
pseudintermedius.

Question 12

What is the 90/60 rule

Answer 12

90% of simple infections with a non resistant organism will respond to appropriate AB tx
60% of resistant infections will respond

Question 13

What are the pitfalls of AB sensitivity testing?

Answer 13

 They underestimate activity at concentration

Question 14

What kind of test is the AGAR DISK DIFFUSION TEST

Answer 14

Qualitative

Question 15

What is the Microdilution Test for Determination of MIC

Answer 15

The lower the MIC value, the more susceptible the isolate is to that drug
MIC50 = inhibits 50% bacteria

Question 16

What types of molecular diagnostic assay are there?

Answer 16

1. Polymerase chain reaction (PCR)
2. Quantitative (qPCR) or real‐time PCR
3. Reverse‐transcription PCR (RT‐PCR)
4. Duplex and multiplex PCR or real‐time PCR
5. DNA sequencing

Question 17

How is FIV diagnosed?

Answer 17

 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

Question 18

Outline respiratory infectious disease testing

Answer 18

 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

Question 19

What are the options for fungal diagnosis?

Answer 19

 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