Typhoid Fever

To cause disease, the S. typhi bacteria must be ingested. This often occurs when a carrier does not wash hands sufficiently well after defecation, and then serves food to others. In countries where open sewage is accessible to flies, the insects land on the sewage, pick up the bacteria, and then land on food to be eaten by humans.

Ingested bacteria head down the gastrointestinal tract, where they are taken in by cells called mononuclear phagocytes. These phagocytes usually serve to engulf and kill invading bacteria and viruses. However, in the case of S. typhi, the bacteria survive ingestion by the phagocytes, and multiply within these cells. This period of time, during which the bacteria are multiplying within the phagocytes, is the 10-14 day incubation period. When huge numbers of bacteria fill an individual phagocyte, the bacteria are discharged out of the cell and into the bloodstream, where their presence begins to cause symptoms.

The presence of increasingly large numbers of bacteria in the bloodstream (called bacteremia) is responsible for an increasingly high fever, which lasts throughout the four to eight weeks of the disease, in untreated individuals. Other symptoms include constipation (initially), extreme fatigue, headache, a rash across the abdomen known as "rose spots," and joint pain.

The bacteria move from the bloodstream into certain tissues of the body, including the gallbladder and lymph tissue of the intestine (called Peyer's patches). The tissue's inflammatory response to this invasion causes symptoms ranging from inflammation of the gallbladder (cholecystitis) to intestinal bleeding and actual perforation of the intestine. Perforation of the intestine refers to an actual hole occurring in the wall of the intestine, with leakage of intestinal contents into the abdominal cavity. This causes severe irritation and inflammation of the lining of the abdominal cavity, called peritonitis, which is frequently a fatal outcome of typhoid fever.

Other complications of typhoid fever include liver and spleen enlargement (sometimes so extreme that the spleen ruptures), anemia (low red blood cell count due to blood loss from the intestinal bleeding), joint infections (especially frequent in patients with sickle cell anemia and immune system disorders), pneumonia (due to a superimposed infection, usually by Streptococcus pneumoniae), heart infections, meningitis, and infections of the brain (causing confusion and even coma). Untreated typhoid fever may take several months to resolve fully.