Fish Immunology (1+1)

Unit 14 - Vaccine

14.1. Introduction
Prevention of disease through vaccination is an important approach to maintain fish health. Exposure of a fish to a pathogen stimulates the immune response and the fish will develop the memory to these pathogens so that it can combat the pathogen very quickly during future encounter. This adaptive immunity is specific against the pathogen and persists for a relatively long period. This persistence is because of an adaptive change in the population of lymphocyte which results from the exposure of the fish to the pathogen that consist the antigen.
Vaccines exploit the two key elements of adaptive immunity and those are specificity and memory. This is because after vaccination the adaptive immune system responds specifically to the invading pathogen and the response become stronger and stronger on the second and subsequent exposure to the pathogen.
Vaccines are preparations of antigens derived from pathogenic organisms, rendered non-pathogenic by various means, which will stimulate the immune system in such a way as to increase the resistance to disease from subsequent infection by a pathogen.
Inducing a protective immune response to a pathogenic organism before the individual becomes naturally exposed to it seems at first sight an highly sensible way of preventing an infectious disease. Unfortunately, achieving this goal not an easy task. vaccines must be safe (no side effects) and potent (induce a high level of protection) and although occasionally it has been possible to achieve these characteristics using simple procedures (usually heat or chemical inactivation of cultures of pathogenic microorganisms) in most cases some degree of antigen purification or enrichment is necessary and the problem lies in identifying the relevant antigens, out of many hundreds present, which are important in stimulating a protective immune response.
Vaccines are generally of two types: Dead vaccines, which are composed of inactivated pathogens or extracts, and Live vaccines, which are attenuated pathogens with no or low virulence."
Dead vaccines

• Inactivated virus or bacterial antigens
• Sub-unit vaccines
• Recombinant vaccines

Live vaccines

• Attenuated live vaccine
• Gene deleted live vaccine

The Ideal Fish Vaccine should have

• Sustained immunity and protection
• Early mass application
• Efficacious for a broad number of species
• Safe to use
• Cheaply available
• Easily produced
• Should have stable antigen
• Can be stored for long time.
• Will not interfere with diagnosis
• Easily licensed