Salmonella in poultry_vaccination

Salmonella Vaccines

Plan of Talk

Aim of Salmonella vaccination Characteristics of an ideal Salmonella vaccine Types of salmonella vaccines– Live attenuated– Inactivated– Subunit

Immunoadjuvants

Aim of Salmonella Vaccination

The aim of vaccination as part of a complex control programs for Salmonella infections in poultry is to: 1. Reduce or prevent the intestinal colonization resulting in

reduced fecal shedding and egg shell contamination. 2. Prevent systemic infection resulting in a diminished

localization in the reproductive tissues.

Plan of Talk


Immunoadjuvants

Ideal Salmonella Vaccine Strain

1. High degree of protection against systemic and intestinal infection.

2. High protective potential against a variety of important serovars (serogroups)

3. Adequate attenuation for poultry, other animal species, humans and the environment.

4. Inactivated and live vaccines should not affect growth of the animal.

5. Vaccine strains should not be resistant to antibiotics.

Cont. …

6. Vaccines should be easy to administer and need to have markers enabling the differentiation from salmonella wild-type strains.

7. Application of vaccines should not interfere with salmonella detection methods.

8. Humoral antibody response after vaccination should be distinguishably from a salmonella wild-type response to allow the use of serological detection methods

9. Attenuated live salmonella vaccine strains should be able to induce the colonisation inhibition effect between salmonella organisms.

Cont. …

10. Salmonella vaccine strains should have preserved the ability to invade the gut as prerequisite to induce the invasion inhibition effect between salmonella organisms

Plan of Talk


Immunoadjuvants

Live Virus Attenuation

The aim of attenuation is to diminish the virulence of the pathogen, but retaining its immunogenicity.

Live Attenuated VaccinesRisk Factors

Several risks are associated with live vaccines, especially in immunocompromised individuals:

1. Some of the structural components of the microorganism used may contain immunosuppressive antigens.

2. Attenuated strains may still have some residual virulence due to an incomplete inactivation.

3. Attenuated strains, after being released into the environment, can recover their virulence in other hosts, or can acquire genes from other microorganisms by natural genetic transfer.

Cont. …

Under these points of view, despite their extended use, the restrictions for the use of attenuated modified organisms in vaccination are becoming more and more stringent.

Live Attenuated VaccinesAdvantages Over Inactivated Ones

1. Easy administration.2. Ability to carry heterologous antigens.3. Capacity to induce cellular and humoral immune responses.

Live Attenuated Vaccines

Empirical Attenuation Methods Attenuated Mutations

Metabolic functions

Virulence factors

Methods of Attenuation



Metabolic functions

Virulence factors

Live Attenuated VaccinesEmpirical Attenuation Methods

The empirical attenuation methods developed by Pasteur and Koch at the end of the twentieth century.

Many successful live viral and bacterial vaccines are produced by repetitive in vitro passage in cell culture.



Metabolic functions

Virulence factors

Live Attenuated VaccinesAttenuated Mutations

The knowledge we have nowadays about genomics allows us to selectively knock out concrete virulence genes.

Cont. …

Salmonella has around 4,500 genes.A change in any gene (mutation) can lead to an alteration in protein.This mutation may change the structure and function of the bacterium.Some mutation may have no effect.

Target Mutagenesis

Specific alteration by genetic manipulation of the genome; Insertion, deletion or framshift changes alter the gene

structure or function.Deletion and insertion frequently used experimentally and

in potential vaccines.

Deletion

A gene or part of it is knocked out. The gene is no longer transcribed, no

RNA and no protein is synthesized.

A B C

A C

Insertion

A foreign piece of DNA is inserted into the targeted gene.

This knocks out the gene function although transcribed RNA no longer encodes correct protein.

Here gene B in an inserted. Insertions are less stable than

deletions, but easier to perform.

A C

A CB

Live Attenuated VaccinesAttenuated Mutations

Advantages of this strategy:1. Some important antigenic determinants can be retained

by attenuated strains that are able to elicit both antibody and cellular immunity.

2. Growing capacity of these attenuated vaccines provides prolonged exposure of antigens to the immune system, resulting in the production of long-lasting memory cells.



Metabolic functions

Virulence factors

Live Attenuated VaccinesAttenuated Mutations/Metabolic Functions

The most widely studied metabolically attenuated strains include mutants deficient in:The biosynthesis of:

1. Aromatic amino acids (i.e. aroA, or aroC and aroD) 2. Purines (purA, purE)

Or in the production of: 3. Adenylate cyclase (cya) 4. Cyclic AMP receptor protein (crp).

Cont. …

In general, auxotrophy can interfere with bacterial replication within the host whenever the required metabolites are:

1. Absent.2. Present in amounts insufficient for bacterial growth in the

compartment where the bacteria reside.



Metabolic functions

Virulence factors

Live Attenuated VaccinesAttenuated Mutations/Virulence Factor

The two more extensively characterized virulence-attenuated vaccine strains have mutations in the two-component regulatory system phoP/phoQ or in Salmonella pathogenicity island 2 (SPI2) loci.

Plan of Talk


Immunoadjuvants

Killed Whole Organisms

To avoid the risk of live vaccines, the use of killed organisms was introduced as safer vaccines.

These vaccines are made from the entire organism but inactivated (killed) by physical or chemical agents.

Cont. …

However, protection induced by bacterins in poultry is generally modest .

The limitations of these kinds of vaccines are:1. Their immunogenicity usually has to be enhanced by co-

administration with adjuvants. 2. Multiple doses are necessary for obtaining long-term

protective immunity; besides, as live vaccines, they may contain immunosuppressive antigens.

Plan of Talk


Immunoadjuvants

Subunit Vaccines

Subunit vaccines contain immunodominant components of the bacteria.

Subunit vaccines may be:1. Crude or purified extracts of the pathogen.2. Synthetic peptides. 3. Obtained by the use of recombinant DNA technology, pure

DNA or RNA.

Cont. …

The primary goal of this approach is: 1. To identify the individual antigens of the pathogen that

are involved in inducing protection.2. Avoiding the immunosuppressive ones.

Cont. …

Combining genomics with our understanding of pathogenesis, it is possible to identify specific proteins from most pathogens that are critical in inducing the right protective immune responses.

Cont. …

The potential advantages are; 1. Vaccine safety.2. The potential abilities to target the vaccines to the site

where immunity is required.3. To differentiate vaccinated animals from the infected ones

through the right selection of the components.

Cont. …

In spite of these data, low levels of resistance against salmonellosis can be induced by administration of flagella, porins or polysaccharide fractions.

The potency of these vaccines is often poor when administered without adjuvant and/or a delivery system.

Cont. …

New generation adjuvants are designed to induce minimal side effects, enhance the duration of the immune response, and concurrently stimulate humoral and cellular immune responses.

Ideal vaccine properties Attenuated Inactivated

Subunit Classical Adjuvant (Alum)

New adjuvants (DDS)

I +++ + + +++

II +++ + + +++

III + ++ ++ +++

IV + + + +++

V + +++ + +++

Strong, protective and long lasting immune response

Right sort of immune responses.

Safe

Single dose of vaccine should confer robust, long-lived immunity. Affordable

I

A good vaccine should stimulate a strong, protective and long lasting immune response. Through the induction of strong, long-lived immunological specific T and B cell memory cells. Measurement of the specific subsets elicited by immunization may guide vaccine development.

II

A good vaccine should induce the right sort of immune responses. The protective immune responses against extracellular pathogens seem to be mediated by long-lived humoral immune responses through the production of antibodies. However, in the control of intracellular infection, cellular immune responses have been shown to be crucial in mediating protection. Therefore, the development of a successful vaccine against those diseases will be facilitated by a thorough understanding of how cellular immune responses are generated and maintained in vivo.

III

An ideal vaccine should be safe. Despite the success of vaccination in eliminating disease and death, the public acceptance of even minor side effects of vaccination is very low. One major challenge faced in developing new vaccines is to achieve strong immunogenicity without increasing reactogenicity.

IV

A single dose of vaccine should confer robust, long-lived immunity. Only a few live vaccines have achieved this goal. In contrast to the results with live vaccines, it has been difficult to promote long lived immunity with a single dose of non-living antigen vaccines. One goal of vaccine development is to rectify this using new adjuvants and antigen delivery systems.

V

An ideal vaccine should be affordable by the population at which they are aimed and should be formulated to resist high and low temperatures to facilitate distribution. This is a main problem for alive attenuated vaccines

Plan of Talk


Immunoadjuvants

Immunoadjuvants

Adjuvants They are defined as a group of structurally heterogenous compounds that enhance or modulate the immunogenicity of the associated antigens.

Cont. …

Despite the recognition of many different types of adjuvant, however, little is known about their mode of action.

Janeway called adjuvants “the immunologists dirty little secret”, because their mode of action is poorly understood.

Cont. …

The events triggered by these immunomodulators appear to come from one or the combination of several of the following effects:

Immunoadjuvants Effects

Adjuvant Effect

Depot Effect Effect On Antigen Presenting Cells (APC)

Nonspecific Immunostimulanting Effect

Particulated Carrier Systems

Immunoadjuvants Depot Effect

If antigen is present in a solution, it is mostly quickly removed by neutrophils and macrophages.

Subsequently, antigens are unable to prime naive T cells.

Following that, the antigens disappear and the immune response is hardly detectable.


Adjuvants, such as:1. Oil emulsions 2. Antigen absorbing aluminium salts

Retain antigen at the injection site, Then, it is released in minute quantities over a prolonged period of time.

These compounds mainly stimulate the production of antibodies by the induction of Th2-lymphocytes.


In the case of use of alum, the mechanism of action seems to be due to Formation of a depot of free alum that will induce the

recruitment and activation of immune cells to the site of inoculation.


Adjuvant Effect




Immunoadjuvants Effect On Antigen Presenting Cells (APC)

The adjuvant induced enhancement of an immune response may be related to the improved delivery of antigens into the draining lymph nodes.

This may be achieved by:1. Facilitating the antigen uptake by APCs.2. Increasing the influx of APCs into the injection site.

Immunoadjuvants Effect On Antigen Presenting Cells (APC)

This results in:1. Increase in the provision of antigen-loaded APCs, and in turn,

effective priming of specific T cells.2. Promoting the activation state of APCs by upregulating

costimulatory signals or MHC expression. 3. This results in the corresponding cytokine release, enhancing

the speed, magnitude and duration of the specific immune response.


Adjuvant Effect




Immunoadjuvants Nonspecific Immunostimulating Effect

Some agents can stimulate the non-specific component of the immune system.

Numerous microorganisms contain “alert signals”, the so called “microbial or pathogen associated molecular patterns” (MAMPs or PAMPs, respectively), which is not present in mammalian cells.

These structures activate immune cells through interaction with specific receptors (toll like receptors, TLRs).

Immunoadjuvants Nonspecific Immunostimulating EffectSome examples are: 1. Lipopolisaccharide (LPS)2. Monophosphoryl lipid A (MPL)3. Flagellin4. Lipoproteins5. Muramil dipeptide (MDP)6. Trehalose dimycolate (TDM), 7. Cpg DNA, among others.Besides, the special chemical nature of some polymers used in the formulation of vaccine delivery systems may also be recognized as scavenger ligands for the APCs.


Adjuvant Effect

Depot EffectEffect On Antigen Presenting Cells

(APC)

Nonspecific Immunostimulantin

g Effect


Immunoadjuvants Particulated Carrier Systems

Particulated Carrier Systems have been proposed to improve the mucosal bioavailability of antigens.These carriers protect labile molecules from degradation in

the gastrointestinal tract. Nanoparticles are submicron-sized colloidal systems that may

protect antigen against chemical, enzymatic or immunological degradation, and facilitates targeting and presentation of antigens to inductive sites of mucosal immune system.

Salmonella in poultry_vaccination

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