Production and efficacy testing of live attenuated and inactivated vaccines against experimental <i>Salmonella</i> Kentucky infection in broiler chickens

Abstract

Background: Salmonella Kentucky is of great veterinary and public health concern and exhibits the capacities to emerge as the most prominent Salmonella serotype in human disease. The objective of this study is to evaluate the efficacy of prepared live attenuated and inactivated vaccines against experimentally induced salmonellosis caused by S. Kentucky in broiler chickens.

Methods: Field isolate of S. Kentucky was obtained from the National Veterinary Research Institute Vom, Nigeria and used in the preparation of experimental vaccines. Broiler chickens purchased and ascertained to be free of Salmonellae were randomly distributed into three experimental groups of 20 chicks each. Five-bromouracil at a concentration of 1000μg/ml was used in attenuation of S. Kentucky in preparation of the live vaccine and 0.6% formaldehyde was used in inactivation of S. Kentucky for preparation of the inactivated vaccine. Group 1 chicks were immunized with the live vaccine subcutaneously at 0.5ml per bird, group 2 received 1ml of the inactivated vaccine subcutaneously, and group 3 served as unvaccinated/control.

Results: There was 100% faecal inhibition and 100% vaccinal efficacy in broiler chickens immunized with the live vaccine on day 56 of age, and 49.6% faecal inhibition and 82.8% vaccinal efficacy in broiler chickens immunized with the inactivated vaccine on day 56 of age when compared with the unvaccinated control. The vaccinated birds also showed higher antibody (IgY) titre levels from day 21 to day 56 of age (p<0.001) on all sampling days when values were compared with the unvaccinated birds.

Conclusion: The interplay between vaccination protocol that includes administration of live attenuated or inactivated S. Kentucky vaccines and developed antibody (IgY) can reduce intestinal colonization by S. Kentucky and subsequent shedding of the serovar in faeces.

Keywords: Salmonella Kentucky, 5-bromouracil, IgY, Antibody, Vaccine