Salmonella Typhi and Salmonella Paratyphi

Salmonella is a gram-negative bacterial genus that demonstrates notable variations in serological reactivities, genetic compositions and pathogenic potential. Based on current methodologies, the genus is separated into two species (Salmonella enterica and Salmonella bongori) and over 2600 serovars. While Salmonella Typhi and Salmonella Paratyphi cause life-threatening typhoid fever and paratyphoid fever, respectively, with estimated annual mortalities of over 150,000 worldwide, nontyphoidal Salmonella (NTS) such as Salmonella Typhimurium and S. Enteritidis are implicated in self-limiting and noninvasive gastroenteritis, which is restricted to the intestine and does not spread to the bloodstream. However, in areas where coinfection with human immunodeficiency virus or malaria often occurs, such as sub-Saharan Africa, NTS strains may sometimes enter the bloodstream and cause bacteremia. Given the clinical significance of typhoid fever due to S. Typhi, this chapter presents an in-depth review on this serovar in relation to its taxonomy, genomics, diagnosis, association with disease, mechanisms of invasion and pathogenesis, and antibiotic and vaccine strategies to minimize its impact, while paratyphoid fever due to S. Paratyphi A and invasive NTS are briefly discussed where appropriate.