Chapter 29 Types of Vaccines

Question 1

What is active immunization in equine medicine?

Answer 1

The use of antigens formulated as a vaccine to stimulate an immune response.

Question 2

What is re-immunization in horses?

Answer 2

Natural exposure to the pathogen in the vaccinated animal, resulting in a secondary immune response and enhanced immunity.

Question 3

What is the ideal characteristic of a vaccine?

Answer 3

It should be safe, induce a potent and long-lasting immune response, not cause clinical signs of the disease, and have minimal or no adverse side effects.

Question 4

What are the types of vaccines licensed for use in horses?

Answer 4

Attenuated or modified live vaccines (MLV), killed or inactivated vaccines, subunit vaccines, nucleic acid-based vaccines, and chimera vaccines.

Question 5

What is an attenuated or modified live vaccine (MLV)?

Answer 5

A vaccine composed of viable attenuated organisms that replicate in host cells and stimulate an immune response without causing disease.

Question 6

What are the principal advantages of MLVs?

Answer 6

They are usually more effective than killed or inactivated vaccines, stimulate both innate and adaptive immune responses, and elicit a greater number of effector mechanisms.

Question 7

What are the disadvantages of MLVs?

Answer 7

Potential for virulence reversion, opportunistic infections in immunodeficient patients, challenging manufacturing, storage, handling, safety, and phenotypic stability issues.

Question 8

What is an example of an intranasal MLV for equine influenza virus?

Answer 8

Flu Avert, attenuated by cold adaptation in embryonated eggs.

Question 9

What is a killed or inactivated vaccine?

Answer 9

A vaccine prepared with microorganisms that are rendered unable to replicate in the host through chemical, heat, or irradiation methods.

Question 10

What are the advantages of killed or inactivated vaccines?

Answer 10

Easier to manufacture, more stable than live vaccines, cannot revert to virulent form, and safer for immunosuppressed animals.

Question 11

What is the main disadvantage of killed or inactivated vaccines?

Answer 11

They usually require multiple injections to elicit an immune response and generally induce less adverse reactions.

Question 12

What is an example of a killed vaccine against West Nile virus?

Answer 12

West Nile Innovator, shown to provide protection against severe disease.

Question 13

What is a protein or subunit vaccine?

Answer 13

A vaccine that combines a portion of the pathogen, such as purified antigens or inactivated toxins, usually combined with an adjuvant.

Question 14

What are the advantages of subunit vaccines?

Answer 14

Increased safety without risk of reverting to virulence, reduced antigenic competition, and potential to differentiate vaccinated from infected animals.

Question 15

What are the disadvantages of subunit vaccines?

Answer 15

Require strong adjuvants, may cause tissue adverse reactions, generally shorter duration of immunity, do not generate mucosal antibodies, and do not replicate intracellularly.

Question 16

What is an example of a subunit vaccine for Streptococcus equi?

Answer 16

Strepvax II, made with a purified M-protein.

Question 17

What is a recombinant vectored vaccine?

Answer 17

A vaccine that uses a virus or bacterium vector to express selected genes from the target pathogen coding for protective antigens.

Question 18

What is the advantage of viral vector vaccines?

Answer 18

Induction of a full range of immune responses, including cytotoxic T lymphocytes (CTLs).

Question 19

What is the main concern with vectored vaccines?

Answer 19

Pre-existing immunity against the vector or potential immune response against the vector limiting response to the target pathogen.

Question 20

What is an example of a canary pox-vectored vaccine for equine influenza virus?

Answer 20

Recombitek rFLU, expressing genes for the hemagglutinin of two influenza virus lineages.

Question 21

What is a DNA-based vaccine?

Answer 21

A vaccine produced by inserting genes coding for protective antigens into bacterial plasmids that enter host cells and direct the synthesis of the vaccine protein.

Question 22

What are the advantages of DNA vaccines?

Answer 22

Safe, stable, easy and inexpensive to manufacture, elicit strong CTL responses, and have intrinsic adjuvant-like activities.

Question 23

What are the disadvantages of DNA vaccines?

Answer 23

Decreased DNA uptake with increased body size, potential for chronic inflammation or autoantibody production, limited to protein immunogens, and potential to affect genes responsible for cell growth.

Question 24

What was the first USDA-approved DNA vaccine for horses?

Answer 24

West Nile-Innovator DNA, for West Nile virus.

Question 25

What is a chimera vaccine?

Answer 25

A hybrid organism created by combining nucleic acid fragments from two or more different organisms, with at least two fragments containing essential genes necessary for replication.

Question 26

What is an example of a chimera vaccine for West Nile virus?

Answer 26

PreveNile, a live West Nile virus flavivirus chimera.

Question 27

What is a marker vaccine (DIVA)?

Answer 27

A vaccine that lacks one or more proteins of the virulent organism, enabling differentiation of vaccinated animals from those infected naturally.

Question 28

What is an example of a marker vaccine for equine arteritis virus?

Answer 28

A recombinant EAV with a silent nucleotide substitution in the nucleocapsid gene.

Question 29

What type of immune responses do vaccines induce?

Answer 29

Development of antibodies, long-lived effector cells, and memory cells.

Question 30

What influences the type of immune response elicited by a vaccine?

Answer 30

The type of vaccine, antigen load, adjuvant or delivery system, and host factors such as genetics, existing immunity, age, immune status, presence of maternal antibodies, and pregnancy status.

Question 31

What is the role of innate immunity in vaccination?

Answer 31

Sending danger signals to the host through stimulation of pathogen recognition receptors (PRRs) of the innate immune cells.

Question 32

What are examples of pathogen recognition receptors (PRRs)?

Answer 32

Toll-like receptors (TLRs) and NOD-like receptors (NLRs).

Question 33

How do live vaccines stimulate the innate immune system?

Answer 33

By containing pathogen-associated molecular patterns (PAMPs) regardless of attenuation.

Question 34

What is the role of adjuvants in inactivated, subunit, or DNA vaccines?

Answer 34

To promote inflammation at the site of vaccination and attract antigen-presenting cells (APCs) that initiate T and B cell activation.

Question 35

What is humoral immunity?

Answer 35

An immune response involving the production of antibodies that control extracellular infections.

Question 36

What happens to antigens after injection of a vaccine?

Answer 36

They reach the regional lymph nodes or spleen, where they are stored on the surface of follicular cells of lymphoid tissues.

Question 37

What are the two signals required for B cell activation?

Answer 37

Binding of antigens to the B cell receptor (BCR) and subsequent interaction with CD4+ T helper cells.

Question 38

What are T cell-independent antigens?

Answer 38

Antigens that induce strong B cell activation without the need of T cell interaction.

Question 39

What is cell-mediated immunity (CMI)?

Answer 39

An immune response involving the activation of T cells to control intracellular pathogens.

Question 40

What is the advantage of modified-live vaccines in inducing CMI responses?

Answer 40

They are effective at inducing CMI responses by activating CD4+ T helper cells and cytotoxic CD8+ T cells.

Question 41

What is the role of antigen-presenting cells (APCs) in vaccination?

Answer 41

To migrate to lymphoid tissues from the site of injection, process the vaccine antigen, and present it to CD4+ T cells via MHC class II molecules.

Question 42

What happens to T cells after activation by APCs?

Answer 42

They undergo clonal expansion and differentiation into effector cells.

Question 43

What is the role of CD4+ T helper effector cells?

Answer 43

To produce cytokines that activate B cells, CD8+ T cells, and macrophages.

Question 44

What is the role of CD8+ T cells (CTLs)?

Answer 44

To mediate cytotoxicity of host cells containing intracellular pathogens.

Question 45

What are the different routes of vaccination?

Answer 45

Intramuscular, subcutaneous, intranasal, oral, sublingual, vaginal, ocular, and aerosol.

Question 46

Why is the route of administration important in vaccine development?

Answer 46

To reach local APCs and induce immunity similar to a natural challenge.

Question 47

What are mucosal vaccines?

Answer 47

Vaccines designed to generate mucosal immunity by mimicking natural infection at the site of pathogen entry.

Question 48

What are examples of mucosal pathogens?

Answer 48

Equine influenza virus (EIV), equine herpesvirus-1 (EHV-1), Streptococcus equi, Rhodococcus equi, Salmonella enterica, and Escherichia coli.

Question 49

What are the advantages of needle-free vaccine delivery?

Answer 49

Efficiency and effectiveness comparable to parenteral administration with a syringe and needle.

Question 50

What are adjuvants?

Answer 50

Substances added to vaccines to enhance and modulate protective immunity.

Question 51

What are the proposed mechanisms of action of adjuvants?

Answer 51

Formation of depot, induction of inflammatory cytokines and chemokines, recruitment of immune cells, enhancement of antigen uptake and presentation, and increased expression of costimulatory molecules and cytokines.