Evaluation of protective efficacy of a novel inactivated Salmonella Pullorum ghost vaccine against virulent challenge in chickens

• A safety enhanced Salmonella Pullorum ghost vaccine candidate is constructed.
• Ghost vaccine induces both humoral and cell-mediated immune responses.
• Ghost vaccine is efficient to prevent pullorum disease in chickens.

Salmonella Gallinarum biovar Pullorum is the causative agent of pullorum disease in poultry, an acute systemic disease that results in a high mortality rate in young chickens. Vaccines have been considered in many developing countries where levels of infection are high and eradication is not a realistic option. An attenuated strain combined with protein E-mediated cell lysis was used to generate a safety enhanced Salmonella Pullorum ghost vaccine. Immune responses and protection induced by ghost vaccine in chickens were investigated following a prime-boost immunization administered via intramuscular and oral routes. Chickens from vaccinated groups showed significant increases in antigen-specific IgG, especially after booster immunization. Lymphocyte proliferation responses were also significantly increased in all immunized groups at 2-weeks post-final vaccination. The Salmonella Pullorum ghost vaccine provided satisfactory protection against virulent Salmonella Pullorum infection, as shown by the robust stimulation of both humoral and cell-mediated immune responses as well as the reduction in the number of bacterial recovered post-challenge. Moreover, the immune effects and survival rates indicated intramuscular injection is more efficient than oral vaccination. In conclusion, our results suggest that Salmonella Pullorum ghosts may be used as a safe and effective novel inactivated vaccine candidate to protect against virulent Salmonella Pullorum infection.