Biotechnology and Bioinformatics (1+1)

4.3.5. Live–attenuated vaccines

Live-attenuated vaccine is a suspension of attended live pathogens that are able to replicate inside the host and induce protective immune response but unable to cause disease.

• They mimic the actual infection by pathogens and hence a small dose of vaccine is enough to induce long lasting protective immune response.
• These live attenuated vaccines can induce both humoral and cell-mediated immune responses.
• These are strong stimulants of cell-mediated immune response. These preferentially enhance T cell prolife rative response relative to B cell responses.
• Some of the conventional live viral vaccines have been produced against VHSV, IHSV and IPNV.
• Avirulent strain s of IHNV are also used as live vaccines.
• Use of VHSV- attenuated strains obtained through serial passage of VHSV in carp-cell line under progressive increase of temperature has been used as live vaccine.
• Protection of goldfish against some common ectoparasites has been observed by intraperitoneal andimmersion immunizations with live tomites of Ichthyophthirius multifiliis and Tetrahymena pyriformis.

Although some of these vaccines are found useful as live vaccines in laboratory, so far none of them has been licensed for field trial. This is because of some of the possible disadvantages that might be associated with this type of vaccines, such as apprehension of such vaccine strains becoming virulent in non-target species,possibility of reversion to pathogenic state and problems associated with residual virulence.