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Background: Salmonella enterica subsp. enterica serovar Typhi is a serovar of the O:9 (D1) serogroup. S. Typhi causes typhoid fever, a life-threatening disease that is characterized by sustained fever as high as 103° to 104° F (39° to 40° C). In developed countries, this serovar is considered rare; however, in developing countries, it is among the top ten Salmonella serovars that caused disease in humans. S. Typhi kills approx. 600.000 people annually. A number of projects have sequenced the genome of strains of S. Typhi; these studies have concluded that S. Typhi is a highly clonal serovar that emerged approx. 30,000-50,000 years ago. In addition, studies have found that horizontal gene transfer plays an important role in the evolution S. Typhi, this included the acquisition of plasmids encoding multiple antibiotic resistant genes in multidrug resistant strains.

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