Development and evaluation of gamma irradiated toxoid vaccine of Salmonella enterica var Typhimurium

Abstract

Development of a single effective vaccine against non-typhoidal salmonellosis is verychallenging due to the presence of hundreds of serovars of Salmonella which areantigenically different from each other. The Salmonella enterotoxin (Stn), a commonvirulence factor occurring amongst a wide range of serovars, used as a formalized toxoidvaccine has been found to be effective against homologous and heterologous serovars.However, the process of formalization has its own drawbacks. Gamma radiation (g) on theother hand is widely used as a safe and convenient method of sterilization worldwide. Inthis experiment we used gamma rays to inactivate the partially purified Stn of Salmonellaenterica serovar Typhimurium (DT 193). The toxoid obtained was tested for itsimmunogenicity and loss of toxicity and then used to formulate a gamma irradiatedtoxoid vaccine (ITST). The efficacy of the developed ITST was tested in Kuroiler, a Broilerbreed, against homologous and heterologous challenges (S. Typhimurium andS. Gallinarum) administered intra-peritoneally and orally. Birds in groups challengedwith S. Typhimurium by both routes recorded protective indices (PI) of 100% while birds ingroups challenged intra-peritoneally with S. Gallinarum recorded PI of 83.33% and thosechallenged orally scored 100%. The overall protective index (PI) being 95.83%. The antibodytitres calculated as geometric mean with standard error at 1:10 4dilutions showed a steeprise after the first dose and peaked at week 6 post primary vaccinations. Thus the ITST wasfound very effective in protecting poultry against both the challenge organisms tested.