Biotechnology and Bioinformatics (1+1)

4.3.13. Vaccine delivery system

A number of methods of administering vaccines to fish have been tried with varying degrees of success. These include:

i) Injection

ii) Oral uptake via food

iii) Immersion in a solution/suspension of the vaccine

iv) Bathing in a very dilute preparation of the vaccine for prolonged periods

v) Spraying or showering the vaccine into fish

vi) Hyposmotic infiltration, and

vii) Anal intubation

It can be administered by injection, by immersion or by spraying directly onto the fish according to what suits an individual farm’s preference.

• For small fish (1.5 to 5 gms) by direct immersion in diluted vaccine (1:10) for 30 secs.
• For larger fish (70-100gms) sprayed with vaccine or immersion for 3-5 secs. Stress should be avoided at the time of handling. Maintain the vaccine solution at the same temperature on the holding tanks, oxygenating the vaccine solution during the vaccination procedure, etc.
• Oral vaccination of fish using Artemia as the vaccine delivery system can also done. When vaccine is given through oral route there is possibility of Ag being degraded by the digestive enzymes in the stomach. New approach involves first feeding the vaccine (a killed bacterial suspension) to the Artemia, and then feeding the Artemia as the first live food to the fry of the species of interest. It is thought that the vaccine becomes incorporated into the lipids of the Artemia and this protects it from the digestive degradation of the fish.
• Immunity in vaccinated animals tends to change with time following vaccination.
• Booster vaccination can be given. Duration of protection depends upon the method of vaccination,the size of the fish, their health status at the time of vaccination and the antigen used to vaccinate them.
• Vibrogen -2 vaccine is produced by Aquatic Health Limited, Greece. The AHL, Canada has developed another vaccine called Lipogen Triple bacterin (a combimnation furunculosis + vibriosis+ hitra bacterin) to protect against furunculosis.

• Gene tic vaccines can be delivered into the host by several routes and methods.
• The main methods of plasmid -DNA delivery is by needle injection or by gene-gun.
• While needle injection requires relatively large amounts of plasmid (50-100 µg), the amount of plasmid required for gene-gun immunization has been titrated down to a few nanogram. When delivered by gene-gun, the plasmid solubilizes when the plasmid coated gold bullet penetrates the cells and thus, plasmid is directly deposited into cells transfecting upto 20% of the cells in the target area. The gold particles directly penetrate due to the force of delivery, thereby increasing the rate of transfection without having to rely on the uptake of DNA by the host cell itself.