Bacterial Vaccines

Question 1

_______ does not always correlate with protection

Answer 1

Immunogenicity

• immunogenicity stimulates an immune response –> some vaccines can stimulate an immune response (antibody), but do not provide protection
• antibody titers do not equal protection

Question 2

Reasons why a vaccine may be highly immunogenic but not protective

Answer 2

• immune response is not directed at the right antigen
• -> ex: LPS is the strongest antigen, but antibodies for LPS are not effective
• wrong type of immunity is stimulated (cell mediated vs humoral)
• immune response does not last long enough

Question 3

Bacterin

Answer 3

Killed bacterial vaccine by either heat or chemical (formalin is common method)

• typically better at stimulating humoral immunity
• generally safe
• immunity may not persist as long as live attenuated vaccines (may require booster)
• immunity is not generated against in vivo expressed antigens

Question 4

Live attenuated vaccine

Answer 4

• usually better at generating cell mediated immunity
• can persist longer in the host, generating longer term immunity
• can generate immunity to in vivo expressed antigens
• depending on pathogen, can be capable of active invasion
• risk of reversion to virulence or causing clinical signs in an immunocompromised host

Question 5

Methods of attenuation

Answer 5

• selection of naturally attenuated strain
• passage on artificial media
• gene mutation: virulence gene, biochemical pathway, regulatory gene

Question 6

Subunit

Answer 6

One or more purified antigens from the bacterial pathogen

• can be protein or polysaccharide (polysaccharide antigens are conjugated to a protein to increase immunogenicity)
• immunity to the antigen must be protective
• has the advantages/disadvantages of bacterins

Question 7

Toxoid

Answer 7

Inactivated toxin

• effective against disease where primary pathology is caused by an exotoxin
• if you block the toxin, then you do not get clinical signs

Question 8

Methods of attenuation

Answer 8

• chemical alteration
• genetic alteration
• use of a non-toxic portion of the toxin

Question 9

Recombinant

Answer 9

Similar to subunit, but the protein are expressed in another bacterial species or a virus

• can be more effective at stimulating cell-mediated immunity (depends on the carrier strain)
• can persist longer than subunit vaccines
• can be a dual vaccine

Question 10

DNA vaccines

Answer 10

Gene encoding the antigen is inserted into a plasmid, and the plasmid DNA is injected directly into the host

• gene is under the control of a strong promoter
• transfected host cells (myocytes) become antigen-presenting cells
• can be effective at stimulating cell-mediated immunity
• always has to be delivered by injection*