Principles and methods of vaccine production and fish immunization

Techniques of immunisation Concept of vaccination  Vaccination - immune response induction Vaccines - preparations of antigens from pathogens, rendered non-pathogenic, stimulates immune system of the animal to increase the resistance to the disease on natural encounter with the pathogen  Vaccines  Ideal vaccines are one which is inexpensive to produce, easy to administer, safe and effective. Role of Vaccines  Primary administration, sensitises the host and builds up a protective immune response by way of memory cells Natural encounter with the pathogen acts as a booster

Vaccination vs chemotherapy: advantages and disadvantages Sl.No Vaccination Chemotherapy / antibiotics 1 Prophylactic: few if any losses from a disease : Curative: some mortalities before treatment is effective 2 Prophylactic for long duration with only one or two treatments Prophylactic for only a short period; constant treatment required 3 Vaccination: all fish receive treatment Mostly antibiotics are given in food, but sick fish are often anorexic and do not receive treatment 4 No toxic side effects, and healthy fish have better growth performance Toxic side effects may be considerable: treatment relies on differential toxicity between host and the pathogen for a therapeutic index; growth often arrested

Vaccination vs chemotherapy: advantages and disadvantages S.No vaccination chemotherapy/antibiotic 5 No accumulation of toxic residues : Toxic residues remain: a time lapse is required between treatment and marketing of fish 6 Pathogen unlikely to develop resistance Many bacteria develop resistance to antibiotics 7 No legal restriction on “safe” vaccines Use of antibiotics are restricted due to risk of development of antibiotic resistant strains 8 Theoretically, can control any disease Chemotherapy limited: cannot control viral diseases 9 No environmental impact Chemicals may disrupt local environment

Types of vaccines Killed vaccines Chemicals– Formalin, chloroform, phenol Physical method - disruption by sonication lysis with sodium hydroxide or the detergent sodium sulphate also used for experimental purposes Heat killing - denatures proteins, oxidises lipids and destroys crucial antigenic sites present on the pathogens.

Types of vaccines Attenuated vaccines Deliver protective antigens to the appropriate site and in the proper context to generate correct immune response. Not normally used in fish due to the scare of reversion Pathogen avirulent in the target species may cause infection in unrelated species and cause widespread infection.

Recent types of vaccines Recently, new trends in vaccination have emerged incorporating latest techniques in biotechnology. Subunit vaccines Synthetic peptides DNA vaccines Mutant viruses.

Characteristics of vaccines Safety Immunogenicity Stimulation of protective immunity Efficacy of Vaccines Specificity

Routes of administration of vaccines in fish The vaccines are administered to the fish in a number of ways Injection immersion hyper osmotic infiltration Bath spray and oral modes

Relative percent survival (RPS) is a measure of the potency of the vaccines and has to be checked invariably for all the vaccines to be marketed. a minimum of 25 fish should be used for the experimentation. % Mortality of vaccinated fish RPS = 1 –  100 % Mortality of controls

Steps involved in the development of fish vaccines Identification of disease problems and potential vaccines Scientific Investigation Disease pathology Aetiology Laboratory challenge system Choice of antigens and vaccines formulation Commercial considerations

Contd….. Production and testing Product licensing Laboratory testing Initial field testing Product licensing Freedom from abnormal toxicity Sterility Safety Potency RPS should be more than 70 % for 10 day observation period

Contd….. Stability Presentation After – Sales service