Enteric bacterial diseases due to Salmonellae and Shigellae remain a serious and frequent cause of morbidity and mortality throughout the World especially in infants and children of developing countries. In addition, these diseases occur in healthy individuals of developed countries under conditions of crowding, such as the Armed Forces recruits, or in institutions where people are treated for chronic diseases. In developing countries, the most frequent and serious of these enteric infections is typhoid fever caused by Salmonelia typhi. Nontyphoidal Salmonellosis occurs mostly in infants and children but also may occur in domesticated animals. Shigellosis is a major cause of morbidity, including decreased growth and mortality among infants and children in the developing World. Despite the century of study after the discovery of these pathogens to-date, there are no licensed vaccines for the prevention of these enteric diseases. An examination of the similarities between the clinical signs, pathology, pathogenesis and protective immunity to nontyphoidal Salmonellae and Shigella has led to a hypothesis that serum IgG antibodies may confer protective immunity to these diseases. Conjugate vaccines for induction of serum IgG antibodies to the O-specific side-chains of the LPS of these pathogens are under development despite the fact that these diseases are considered intraluminal infections, which ought to require secretory and/or cellular immunity.
