Typhoid Fever

Typhoid fever

Typhoid fever is a severe infection causing a sustained high fever, and caused by the bacteria Salmonella typhi —similar to the bacteria spread by chicken and eggs resulting in "Salmonella poisoning," or food poisoning. S. typhi bacteria, however, do not multiply directly in food, as do the Salmonella responsible for food poisoning, nor does it have vomiting and diarrhea as the most prominent symptoms. Instead, persistently high fever is the hallmark of infection with Salmonella typhi.

S. typhi bacteria are passed into the stool and urine of infected patients, and may continue to be present in the stool of asymptomatic carriers (individuals 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.

The disease is passed between humans, then, through poor hygiene , such as deficient hand washing after toileting. Individuals who are carriers of the disease and who handle food can be the source of epidemic spread of typhoid. One such individual was the inspiration for the expression "Typhoid Mary," a name given to someone with whom others wish to avoid all contact. The real "Typhoid Mary" was a cook named Mary Mallon (1855–1938) who lived in New York City around 1900. She was a carrier of typhoid and was the cause of at least 53 outbreaks of typhoid fever.

Typhoid fever is a particularly difficult problem in parts of the world with less-than-adequate sanitation practices. In the United States, many patients who become afflicted with typhoid fever have recently returned from travel to another country, where typhoid is much more prevalent, such as Mexico, Peru, Chile, India, and Pakistan.

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 travel 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.

Samples of a patient's stool, urine, blood, and bone marrow can all be used to culture (grow) the S. typhi bacteria in a laboratory for identification under a microscope . These types of cultures are the most accurate methods of diagnosis.

Chloramphenicol is the most effective drug treatment for S. typhi, and symptoms begin to improve slightly after only 24–48 hours of receiving the medication. Another drug, ceftriaxone, has been used recently, and is extremely effective, lowering fever fairly quickly.

Carriers of S. typhi must be treated even when asymptomatic, as they are responsible for the majority of new cases of typhoid fever. Eliminating the carrier state is actually a difficult task, and requires treatment with one or even two different medications for four to six weeks. In the case of a carrier with gall stones, surgery may need to be performed to remove the gall bladder, because the S. typhi bacteria are often housed in the gall bladder, where they may survive despite antibiotic treatment.

Hygienic sewage disposal systems in a community, as well as hygienic personal practices, are the most important factors in preventing typhoid fever. For travelers who expect to go to countries where S. typhi is a known public health problem, immunizations are available. Some of these immunizations provide only short-term protection (for a few months), while others may be protective for several years. Immunizations that provide a longer period of protection, with fewer side effects from the vaccine itself, are being developed.

See also Antibody formation and kinetics; Bacteria and bacterial infection; Immunity, active, passive and delayed; Immunochemistry; Immunogenetics; Immunology; Vaccination