Typhoid fever is a severe bacterial infection spread through water or food contaminated with human waste. The typhoid fever is caused by Salmonella enterica serovar Typhi (S. Typhi), a highly virulent and invasive enteric bacterium.

S. Typhi can be found in food or water contaminated with the feces or urine of infected individuals. Polluted water is the most common source of typhoid. However, fruits and vegetables fertilized by human waste, shellfish from sewage contaminated beds, and contaminated milk and milk products have also been found to be sources of infection.

The S. Typhi genome was sequenced nearly a decade ago, and is known to share the majority of its genes with Enterica coli and Salmonella typhimurium. However, over time, S. Typhi evolved to become more pathogenic than other Salmonella serovars and developed the ability to invade other tissues, including the liver, spleen, gall bladder, and bone marrow.

Notably, the genome continues to evolve in order to evade antibiotic treatment. Currently, resistance to first-line antibiotics is widespread, requiring new and more expensive antibiotics for treatment and increasing patient hospitalization rates.

Paratyphoid

Paratyphoid is a similar disease to typhoid fever, but is caused by a different genus of bacteria. In typhoid-high burden communities, paratyphoid infections caused by the bacterium Salmonella enterica serovar Paratyphi are also common. Paratyphoid fever can be caused by any of three serotypes of S. enteritidis Paratyphi A, B or C.

Paratyphoid fever infections cause similar symptoms to S.Typhi, but are generally less severe. Paratyphoid fever also typically has a shorter duration than typhoid.