immuno diagnostics

Question 1

list methods of detecting pathogens

Answer 1

Culture
* Grow the pathogen in the lab.
* Advantages: can identify the organism and test antibiotic sensitivity.
* Disadvantages: takes at least 2 days, needs special facilities and trained staff.

Antigen detection
* Looks for a piece of the pathogen (protein, carbohydrate, etc.).
* Methods:ELISA (lab-based). Lateral flow tests (like COVID test kits). Latex agglutination (beads clump if antigen present).
* Example: Taylorella equigenitalis detection in horses.

Genetic material
* Detect DNA or RNA (PCR and similar methods).
* Very sensitive, but can sometimes detect “dead” pathogen → doesn’t always mean active infection.

Inflammatory markers (non-specific, but help monitoring)
* Fibrinogen.
* CRP (dogs, pigs).
* Serum amyloid A (SAA) (cats, horses, cows).
* Haptoglobin (cows).
* Pig-MAP (pigs).

Question 2

what are antibody tests

Answer 2

Show if an animal has been exposed to a pathogen.

Limitations: can’t always tell if infection is current or past.

Traditional tests:

Agglutination.

Haemagglutination inhibition.

Complement fixation.

ELISA types:

Indirect ELISA → detects antibodies in sample.

Competition ELISA → sample antibody competes with a labelled antibody.

Examples: African swine fever, Influenza A.

IgM antibody capture (IMAC) ELISA → detects recent/active infection.

Example: screening cats for toxoplasmosis before ciclosporin treatment.

Indirect tests (immune response rather than pathogen):

TB testing

SICCT (single intradermal comparative cervical tuberculin test): type IV hypersensitivity.

IFN-γ test: measures cell-mediated response.

Question 3

what is sensitivity and specificity referring to

Answer 3

Sensitivity = how well it detects diseased animals (avoids false negatives).

Specificity = how well it excludes healthy animals (avoids false positives).

Example: A test with sensitivity 90% and specificity 96.5% → about 1 in 30 healthy cattle will test false positive.