Immuno-diagnostics Flashcards
Why can’t clinical signs alone be used for definitive diagnosis?
Many infectious diseases share non-specific signs
Confirmatory testing (culture, antigen, or antibody detection) is required for diagnosis
What are the advantages and limitations of pathogen culture?
Advantages:
- Allows further characterisation of pathogens
- Enables antibiotic sensitivity testing
Limitations:
- Time-consuming – usually takes at least 2 days
- Requires specialised facilities & trained personnel
What are common antigen detection methods in veterinary practice?
Laboratory-based tests
- ELISA
Patient-side tests
- Lateral flow devices
- Latex agglutination tests
What is a molecular method for pathogen detection?
Polymerase Chain Reaction (PCR)
Detects specific genetic material from pathogens
Highly sensitive and specific
What are some key inflammatory markers used in animals?
Fibrinogen
C-reactive protein (CRP) – Used in dogs & pigs
Serum amyloid A (SAA) – Used in cats, horses, cows
Haptoglobin – Used in cows
Pig major acute phase protein (pig-MAP) – Used in pigs
What are some traditional antibody testing methods?
Agglutination/ Haemagglutination Inhibition
Complement Fixation Test (CFT)
Used for detecting antibodies in response to infections
What are the different types of ELISA antibody tests?
Indirect ELISA – Detects host antibodies against pathogen
Competition ELISA – Used for detecting specific antibodies against viruses
Describe indirect ELISA antibody testing
Antibodies are added which detect animal’s antibodies against pathogen
When they bind, AB causes colour change in substrate
e.g., ELISA for African swine fever virus antibodies
Describe competition ELSIA antibody testing
AB is added that competes with animals own antibodies to bind to antigen => colour change
Good for non-species specific pathogens
e.g., ELISA for influenza A virus antibodies
What is an IgM antibody capture ELISA used for?
Detects active infection by identifying IgM antibodies
e.g. Used for toxoplasmosis screening in cats before treating with ciclosporine
Describe IgM antibody capture ELISA
- AB coated onto plate that is specific to IgM
- Add antigen of interest & see if it has been captured & bound by IgM on plate
- Specific AB to antigen is added with associated substrate that changes colour when attached to antibody-antigen complex
What are the two main diagnostic tests for TB in cattle?
Single Intradermal Comparative Cervical Tuberculin Test (SICCT)
- Measures type IV hypersensitivity reaction
Interferon-Gamma (IFN-γ) Test
- Measures cell-mediated immune response to TB antigens
What do sensitivity and specificity mean in diagnostic testing?
Sensitivity – Ability to correctly identify infected animals
Specificity – Ability to correctly identify uninfected animals
Why is it difficult to detect a virus immediately after exposure?
Initially, virus replication is low, so detection is unlikely
As replication increases, virus can be detected in respiratory secretions or other samples
Infectious virus detection lasts only few days, but PCR-based detection lasts longer due to high sensitivity
How do antibody levels change after infection?
IgM appears first but declines quickly
IgG follows later & remains for longer
If animal was previously infected or vaccinated, IgG may already be present
What is seroconversion, and how is it detected?
Seroconversion is the significant increase in antibody levels following infection
Paired serum samples are needed:
- Acute sample: Taken early, before antibody response
- Convalescent sample: Taken 10-14d later to detect AB increase
4-fold rise in antibody titre is considered diagnostic
Why are paired serum samples necessary for diagnosing recent infections?
Single IgG test can’t distinguish between past & current infection
Paired samples show increase in AB titre, confirming recent infection
Without seroconversion, IgG may simply reflect prior exposure or vaccination
What is the purpose of testing inflammatory markers in disease?
Detects early inflammatory responses in disease
Useful for prognostic monitoring (assessing response to treatment)
Not specific for infection – also elevated in other inflammatory conditions
Why is selecting the correct sample type important for diagnostic testing?
Different pathogens require specific sample types
Blood used for detecting pathogens in circulation or ABs
Mucosal swabs target surface-residing pathogens
Respiratory sampling helps identify deep-seated infections
Less invasive samples (e.g. saliva, milk) are easier to collect and useful for herd monitoring
When are mucosal swabs appropriate, and how should they be handled?
Used when pathogens are found on mucosal surfaces (e.g. nasopharyngeal or vaginal swabs)
Place into correct transport medium to preserve sample
For virus isolation, transport medium should contain antibiotics to prevent bacterial overgrowth
For bacterial culture, avoid antibiotics in transport medium
How can samples be collected from the respiratory tract?
Tracheal wash via endoscopy collects deeper respiratory samples
Helps detect pathogens causing lower respiratory infections
When is choosing which animal to sample important?
For individual pets, there is no choice—sick animal is sampled
In group settings (e.g. stables, kennels, herds), choosing right animal(s) to sample is crucial for tracking disease spread
What is index case?
Index case is first detected infected animal
Should be sampled first
What happens if the index case is missed?
If infected animal isn’t noticed or sampled, it may spread disease (e.g. equine influenza has R₀ of 2, meaning 1 horse infects 2 more)
Newly infected horses may show clinical signs few days later, triggering sampling
At this stage, sample:
- Newly symptomatic horses for nasal swabs & acute blood
- Original index case (if still present) for comparison
Why is it important to test both symptomatic and asymptomatic animals?
Some animals may shed virus without showing signs
Testing helps identify & isolate infected but asymptomatic carriers
Helps prevent further spread and guides treatment decisions
