Biotechnology and Bioinformatics (1+1)

4.3.4. Killed whole cell vaccines

Killed whole cell vaccine is a suspension of heat or chemical killed pathogens that are able to induce specific protective immune response against those pathogens when administered into the host.

• These have been of great use in controlling some of the important fish bacterial pathogens such as, V. anguillarum, V. salmonicida, V. ordalli, Y. ruckeri,and A. salmonicida.
• All these killed vaccines are formalin inactivated whole cell vaccines administered with orwithout adjuvants and are commercially available.
• These bacterial vaccines are highly immune protective, and are cheap to produce, but are not known at present as to what specific antigens of these vaccines are involved in offering protection.
• Although in many cases it is believed that the protective substances are lipopolysaccharides.

Killed vaccines have been developed for some pathogenic fish viruses such as infectious pancreatic necrosis virus (IPNV), infectious haematopoietic necrosisvirus (IHNV), viral haemorrohagic septicaemia virus (VHSV) and spring viremia of carp virus (SVCV).

• Injection of rainbow trout fry with the inactivated IPNV offers good protection in rainbow trout but when administered in brook trout with Freund’s complete adjuvant it induces strong humoral response with poor protection.
• Successful use of killed VHSV in rainbow trout has also been recorded.
• Formalin-inactivated IHNV has been found to protect rainbow trout against lethal IHNV when immunized at high concentration.
• Although all these above vaccines look promising at laboratory scale none of them has been commercialized.
• It is only the killed vaccine of spring viremia of carp virus (SVCV) that was commercially available for some years. This vaccine comprises of two inactivated strain s of SVCV emulsified in oil.

Disadvantages of using killed virus vaccines

• high cost of their production in cell culture, and
• their cumbersome method of purification and
• delivery.
• In gene ral, killed vaccines alone trigger only the humoral immune response and not the cell-mediated immune response. Further, this induces protective immunity, which fades away over time and needs to be given in booster doses.