Salmonella Vaccines for Animals and Birds and Their Future Perspective

Vaccines are the most powerful biologicals which have modulated the economic, social and cultural life of human beings. Certain diseases have haunted humanity for centuries but are now extinct due to vaccines. On the other hand, some diseases such as salmonellosis, that were uncontrollable in the past, still cause pandemics today. There are more than 2500 serovars of Salmonella and vaccines made from any one serovar do not confer cross-protection against another, no matter how much antigenic similarity there is between the two. Salmonella strains are able to cause disease and to adapt to different types of animals whilst still maintaining their zoonotic and interspecies transfer potential. Three major types of vaccines are being used to control salmonellosis: killed bacteria, subunit vaccines and live attenuated vaccines. Effective vaccines against some host adapted and common serovars have been developed but their use has led to the emergence of other serovars. The problem has become more complex because increased international trade and travel has helped Salmonella strains to cross continental boundaries. It seems unlikely that we will be able to develop an effective Salmonella vaccine in the near future that is able to control all forms of salmonellosis, even in a single animal species. Recent advances in Salmonella vaccines will be reviewed including the use of Salmonella as vector for delivery of multivalent DNA and recombinant vaccines for controlling salmonellosis and other infectious diseases as well as for the control of cancer.