Typhoid fever: "you can't hit what you can't see".

The host restricts dissemination of invasive enteric pathogens, such as non-typhoidal Salmonella serovars, by mounting acute inflammatory responses characterized by the recruitment of neutrophils. However, some enteric pathogens, such as Salmonella enterica serovar Typhi (S. typhi), can bypass these defenses and cause an invasive bloodstream infection known as typhoid fever. Recent studies on virulence mechanisms of S. typhi suggest that tight regulation of virulence gene expression during the transition from the intestinal lumen into the intestinal mucosa enables this pathogen to evade detection by the innate immune system, thereby penetrating defenses that prevent bacterial dissemination. This example illustrates how the outcome of host pathogen interaction at the intestinal mucosal interface can alter the clinical presentation and dictate the disease outcome.