Typhoid fever is an acute illness associated with fever caused by the Salmonella typhibacteria. It can also be caused by Salmonella paratyphi, a related bacterium that usually causes a less severe illness. The bacteria are deposited in water or food by a human carrier and are then spread to other people in the area.
No animals carry this disease, so transmission is always human to human. If untreated, around 1 in 4 cases of typhoid end in death. If treatment is given, less than 4 in 100 cases are fatal. S. typhi enters through the mouth and spends 1-3 weeks in the intestine. After this time, it makes its way through the intestinal wall and into the bloodstream.
From the bloodstream, it spreads into other tissues and organs. The immune system of the host can do little to fight back because S. typhi can live within the host's cells, safe from the immune system.
