Serology

Primary Antibody response:

7-10 days

smaller peak response

IgM > IgG highest

lower average affinity

Memory (Secondary) Response

1-2 days

larger peak response

IgG > IgM

higher average affinity

high IgM (relative to IgG)

Indicates a recent or first-time exposure to the antigen

Typical of the primary immune response

high IgG (relative to IgM)

Indicates a memory response following re-exposure

Seen in the secondary immune response

In some infections with persistent or chronic antigenic stimulation…

Both IgM and IgG may remain detectable for an extended period

Rabies vaccines in dogs

Start at 3 months old

Puppies are considered protected by 28 days later

Boost at 1 year after the first vaccine

Serology

is the study of serum and other body fluids

In practice, serology means

refers to the diagnostic identification of antibodies in the serum

What are serotypes(serovars)?

Distinct groupings within a microorganism species (like bacteria or viruses) or immune cells, classified by shared surface antigens (proteins/molecules) that trigger specific immune responses

Why do serotypes matter?

Serotypes can be differentiated using serological assays such as: Neutralizing antibodies, Agglutination tests, Other well-designed serological assays

Different serotypes express?

distinct surface antigens, These unique antigens trigger distinct, non-cross-reactive antibody responses

Serovar example: Leptospira

There are more than 200 serovars for Leptospira

We have animal Leptospira vaccines that protect against several but not all serovars

Rabies virus:

All rabies virus variants (genotypes) can be neutralized by the same antibodies generated by the rabies vaccine (killed rabies virus). This explains why having 1 serotype allows for the same vaccine to be effective against all rabies genotypes

What is seroconversion?

the point at which specific antibodies become detectable in the blood serum following infection or vaccination

marks the transition from being seronegative to seropositive

When does seroconversion occur?

Typically occurs within 1-2 weeks after exposure in most infected or vaccinated individuals

Factors that influence detection

Seroconversion Assay sensitivity (ability to detect low levels of antibody) and Assay specificity

Seroconversion does not inherently confer protection

Only some types and concentrations of antibodies may confer protection

Maybe cell mediated immunity is required for protection

Not all individuals who are infected, vaccinated or have disease due to an infection undergo…

seroconversion

Interpreting serology results

Lack of detection of antibody to an antigen may not mean the animal is not exposed (or maybe infected)

It could be too early for a primary antibody response to be detected

The amount of antibody (to a particular antigen) in a serum sample is determined by?

testing increasing dilutions of the serum for antibody reactivity (a positive test result) to know the known antigen of interest

Titration:

the dilution series of the serum

Titer:

The reciprocal of the highest dilution of serum that gives a positive test result

Dilution series

A 1:10 dilution of a serum sample is: 1 ml of serum + 9 mls of diluent = 1:10

Acute serum:

collected early after onset of illness

Convalescent serum:

collected 14-21 days later that is 2-3 weeks

A four-fold rise (four dilutions) OR GREATER in titer (antibody to specific antigen) from acute to convalescent serum means?

Usually reflects a primary active infection (testing 2-3 weeks apart)

If the antibodies are due to the current infection they should?

should be rising from zero or very low to high (4-fold increase or greater)

If the 2 titers remain level or the second one falls it is probably?

a past infection (or past vaccination) or background/cross-reacting antibodies

Serology for Introducing New Animals

New animals screened by serology to prevent introducing pathogens into the herd/flock

Two negative serology tests, 2-4 weeks apart

Role of serology in herd/flock

Serology (acute and convalescent samples) can detect antibodies to multiple agents in a herd

Useful when multiple animals can be tested and when highly contagious infections require quarantining exposed animals

Paired serology

acute + convalescent samples

The infected animal can infect a new vector before it?

seroconverts and maybe before it shows clinical signs