Salmonella vaccines in poultry: An update on the current status.

Salmonella can cause significant infections in poultry, including fowl typhoid and pullorum disease, while Non-Typhoidal Salmonella (NTS) causes mild to severe diarrheal diseases and is potentially zoonotic. NTS, a significant cause of gastroenteritis in humans, is often underestimated in developing countries, where contaminated chicken or poultry products are the main drivers of its spread. Various whole-cell killed, live-attenuated, or subunit vaccines are available for poultry salmonellosis. Poultry producers prefer killed vaccines owing to their safety and minimal public health risks. However, killed vaccines do not eliminate the carrier status and require parenteral administration. Live-attenuated vaccines are supposed to elicit strong mucosal and cell-mediated immune responses, which may enhance protection; however, their use requires additional biosafety considerations. In addition, certain subunit vaccines, including OMV-based vaccines and nanoparticle vaccines, can also elicit strong mucosal, humoral, and cell-mediated immune responses. Vaccine platforms, including mRNA vaccines and multi-epitope-based vaccines, have not been extensively studied against poultry salmonellosis, though they can be evaluated to develop effective vaccine formulations. Challenges, including spatiotemporal variation in serovar distribution, operational difficulties in implementing vaccination programs, and limited awareness among poultry producers and the public, need to be addressed alongside considerations of vaccine efficacy and longevity. This review provides a comprehensive overview of the available Salmonella vaccines for poultry, including their merits and demerits, recent advancements in vaccine development, and the challenges associated with implementing immunization programs, particularly in developing countries.