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Typhoid fever is a severe infection caused by a bacterium, Salmonella typhi. S. typhi is in the same family of bacteria as the type spread by chicken and eggs, commonly known as "salmonella poisoning," or food poisoning. S. typhi bacteria do not have vomiting and diarrhea as the most prominent symptoms of their presence in humans. Instead, persistently high fever is the hallmark of S. typhi infection.
S. typhi bacteria are passed into the stool and urine of infected patients. They may continue to be present in the stool of asymptomatic carriers, who are persons who have recovered from the symptoms of the disease but continue to carry the bacteria. This carrier state occurs in about 3% of all individuals recovered from typhoid fever.
Typhoid fever is passed from person to person through poor hygiene, such as incomplete or no hand washing after using the toilet. Persons who are carriers of the disease and who handle food can be the source of epidemic spread of typhoid. One such individual gave her name to the expression "Typhoid Mary," a name given to someone whom others avoid.
Typhoid fever is a particularly difficult problem in parts of the world with poor sanitation practices. In the United States, most patients who contract typhoid fever have recently returned from travel to another country where typhoid is much more common, including Mexico, Peru, Chile, India, and Pakistan.
S. typhi must be ingested to cause disease. Transmission often occurs when a person in the carrier state does not wash hands thoroughly (or not at all) after defecation and serves food to others. This pathway is sometimes called the fecal-oral route of disease transmission. In countries where open sewage is accessible to flies, the insects land on the sewage, pick up the bacteria, and then contaminate food to be eaten by humans.
After being swallowed, the S. typhi bacteria head down the digestive tract, where they are taken in by cells called mononuclear phagocytes. These phagocytes are cells of the immune system, whose job it is to engulf and kill invading bacteria and viruses. In the case of S. typhi, however, the bacteria are able to 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- to 14-day incubation period of typhoid fever. When huge numbers of bacteria fill an individual phagocyte, they spill 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 (bacteremia) is responsible for an increasingly high fever, which lasts throughout the four to eight weeks of the disease in untreated individuals. Other symptoms of typhoid fever include constipation (at first), extreme fatigue, headache, joint pain, and a rash across the abdomen known as rose spots.
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 response to this invasion causes symptoms ranging from inflammation of the gallbladder (cholecystitis) to intestinal bleeding to 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 leakage causes severe irritation and inflammation of the lining of the abdominal cavity, which is called peritonitis. Peritonitis is a frequent cause of death from typhoid fever.
Other complications of typhoid fever include liver and spleen enlargement, sometimes so great that the spleen ruptures or bursts; anemia, or low red blood cell count due to blood loss from the intestinal bleeding; joint infections, which are especially common in
Author Info: Rosalyn Carson-DeWitt MD, The Gale Group Inc., Gale, Detroit, Gale Encyclopedia of Medicine, 2002
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