PRODUCTION AND TESTING THE EFFICACY OF LIVE ATTENUATED AND INACTIVATED VACCINES AGAINST EXPERIMENTAL SALMONELLA KENTUCKY INFECTION IN BROILER CHICKENS
Salmonellosis is of major veterinary and public health importance. Salmonella Kentucky exhibits the potential to emerge as the most prominent Salmonella serotype in human disease. The aim of this study was to evaluate the efficacy of prepared live attenuated and inactivated vaccines against salmonellosis caused by Salmonella Kentucky. Field isolate of Salmonella Kentucky was obtained from the National Veterinary Research Institute Vom, Nigeria. Broiler chickens were purchased and ascertained to be free of Salmonellae and distributed into three experimental groups. 5-bromouracil (Sigma Aldrich) at a concentration of 1,000 μg/mL was used to attenuate the bacteria for the preparation of the live vaccine and 0.6 % formaldehyde (Sigma Aldrich) was used to inactivate the bacteria for preparation of the inactivated vaccine. The birds in the first group were immunized using the live attenuated vaccine administered subcutaneously at 0.5 mL per bird at day 11 of age and a booster of same dose was given at day 25. The birds in the second group received 1 mL of the inactivated vaccine subcutaneously at day 11 of age and a booster of same at day 25. Birds in the third group served as unvaccinated/control. The birds in both vaccinated and unvaccinated groups were challenged orally with 1 mL of the field isolate containing 5 x 107 CFU/mL of Salmonella Kentucky suspension at day 32 of age. There were no mortalities recorded in the immunized groups. The degree of protection was assessed in birds using the antibody (IgY) titre developed in serum and the caecal Salmonella Kentucky load present in faeces. Broiler chickens immunized with the live attenuated vaccine preparation at day 54 of age had no Salmonellae present in faeces, equivalent to 100 % inhibition and vaccinal efficacy. Also, broiler chickens immunized using the inactivated vaccine showed a decline in faecal Salmonellae shed; 82.82 % vaccinal efficacy at day 56 of age when compared with the control. Over all the faecal Salmonella count in Cloacal swab of birds immunized with experimental vaccines at day 56 of age was lower than the unvaccinated group; 0 CFU/mL for the live attenuated vaccine and 3.5 x 102 for the inactivated vaccine groups while the control had 1.33 x 105 CFU/mL. The vaccinated birds also showed a higher antibody (IgY) titre levels from day 21 of age to day 56 of age (P < 0.001) on all sampling days when values were compared with the unvaccinated birds. In conclusion, the interplay between vaccination protocol that includes administration of live attenuated or inactivated Salmonella Kentucky vaccines and developed antibody (IgY) titre can reduce Caecal colonization by Salmonella Kentucky and shedding of the serovar. Further studies should be carried out on experimental vaccine to establish its safety and shelf life, also a detailed antibody response, induced cell mediated immunity and other complement cascade interactions be studied.