Diagnostics: Serology and Immunohistochemical Flashcards
Pathognomonic signs
Diagnostic sign marking the presence of a particular disease
Silver dollar plaques on a horse indicate…
Dourine: Chronic veneral disease
Trypanosomoma equiperdum
Pink diamond-shaped skin lesions in pigs indicate…
Swine erysipelas: diamond skin disease
Erysipelothrix rhusiopathiae
Types of specimens for collection
Tissues Blood Scrapes/Swabs/Impression Transudate/Exudates Urine/misc fluids Feces Vomit/sputum Blood
Factors that influence specimen collection choice
Clinical symptoms
Duration of infection
Diagnostic tests to be performed
What is the first step in accurate diagnostic testing?
Proper specimen collection!
Specimens for BACTERIAL infections
Dog/Cat: skin scrape, hair, ear swab, urine, blood, wound swabs
Horses: nasal swabs and fluids, wound swabs
Food animals: Post mortem tissues/organs, milk
Specimens for PARASITIC infections
*base on parasitic life cycle
Feces Vomit Sputum Blood Urine Skin scrape Muscle biopsy Post mortem samples
Specimens for VIRAL infections
Feces Blood Nasal, tracheal, eye swabs Sputum Post mortem samples
At what phase of disease is the best time to collect samples?
During the acute phase
Goals of aseptic sampling
Reduce/avoid contamination with normal flora
Avoid environmental contamination
Reduce risk of secondary infection
Correct handling and transport depends on…
Pathogen type
Specimen type
Diagnostic tests being performed
3 types of diagnostic tests
Phenotypic
Molecular
Serology/immunohistochemical
What do immunohistochemical tests detect?
Pathogen-specific antibodies or antigens
Why choose immunohistochemical methods?
Quickly diagnose threatening agents
Organisms take too long to culture (mycobac)
Organisms are difficult to culture (Rickettsiae)
Unculturable organisms (Clostridium piliformis)
The ability of the test to detect very minute quantities of antigen or antibody
Sensitivity
The ability of the test to detect reactions between homologous Ag and Ab, minimizing false positives
Specificity
What specimens detect antibodies?
Blood, tissue fluids
serology
What specimens detect antigens?
Areas of infection where pathogens replicate and are present
serotyping
Best time to collect to detect antigen
Acute phase
Best time to collect to detect antibody
10-14 days after infection
Indicators for active or recent infection
Pathogen detection
Clinical symptoms
Antibody titer
*number of circulating antibodies will decrease over time. Presence may not indicate active infection. Absence may not mean absence of pathogen
What test detects Ab response to viruses, parasites, bacteria or fungi?
ELISA (Enzyme Linked ImmunoSorbent Assay)
Benefits of ELISA
High sensitivity and specificity
Quantitative: indicates amount of Ag or Ab present
Types of ELISA
Direct Indirect Sandwich Lateral-flow IDEXX snap test
In which type of ELISA is the antigen bound to the solid phase, washed, then directly incubated with conjugated antibody?
Direct
Features of DIRECT ELISA
qualitative or quantitative Ag detection
antibody screening
epitope mapping
What makes INDIRECT ELISA more sensitive than direct ELISA?
Addition of labeled second antibody enhances the signal of the primary antibody
What type of ELISA was designed for soluble antigens or low concentrations, and requires a compatible antibody pair that recognizes different epitopes on the same antigen?
Sandwich
Variation of ELISA that is mostly qualitative or semi-quantitative and confirms presence or absence of target molecule
Lateral-Flow Immunoassay
Benefits of lateral flow immunoassay
User friendly One-step analysis Low cost Versatile Rapid
What is a variation of the lateral flow tests that uses bidirectional flow and integrates a wash step to minimize false positives?
IDEXX snap tests
Benefits of IDEXX snap tests
Integrated wash step Increased sensitivity Small amount of antigen will work Variety of tests Some tests detect multiple diseases
Benefits of Immunofluorescence
Localize pathogen
Detect autoimmune, viral, diseases (HW, FIP)
High sensitivity and specificity
What test employs a visible clumping of particulate Ag with its specific Ab, forming a visible lattice?
Agglutination test
Benefits of agglutination
Easy to make
Easy to use
Cheap
Clearly visible reaction
Disadvantages of agglutination
Low sensitivity
Low specificity
Affected by vaccine-induced Ab
Benefits of immunochemical methods
Good for non-culturables Most have high sensitivity Most have high specificity Mid to high volume testing possible Indication of immune response
Disadvantages of immunochemical methods
Detection of Ab not always indicative of active infection
Detection limit: Ab might not be detected in samples taken early in infection
Ab can reflect multiple pathogens that have the same antigen
