Vaccination for control of Salmonella in poultry

Salmonella spp. are facultative intracellular pathogens causing localised or systemic infections, in addition to a chronic asymptomatic carrier state. They are of worldwide economic and public health significance. In poultry, which represent important sources of cheap protein throughout the world, fowl typhoid and pullorum disease continue to cause economic losses in those parts of the world where the poultry industries are continuing to intensify and where open sided housing is common. A number of serotypes that cause human gastro-enteritis are also increasing. The costs or impracticality of improvements in hygiene and management together with the increasing problems of antibiotic resistance suggest that vaccination in poultry will become more attractive as an adjunct to existing control measures. However, our understandings of the immunology of Salmonella infections in poultry is rudimentary and much poorer than that of equivalent infections in mice and live vaccine development for poultry has therefore been largely empirical. In addition to the killed Salmonella vaccines which have been used over the past few years with variable efficacy, a number of live vaccines have become available and some new vaccines will appear on the market over the next few years. These new vaccines should fulfil the criteria of efficacy, safety and compatibility with existing systems for monitoring infection before they are released on to a mass market. In this review we attempt to summarise the current understanding of Salmonella immunology in poultry together with the progress that has been made in poultry vaccine development.