Typhoid fever is a systemic infection caused by the bacterium Salmonella typhi, usually manifested by the slow onset of a sustained fever and a variety of other symptoms including headache, cough, digestive disturbances, abdominal pain, and profound weakness. In a minority of sufferers, findings more specific for typhoid fever may be present, such as enlargement of the spleen or liver, or a characteristic “rose spot” rash. Untreated, the illness lasts 3 to 4 weeks; it claims the lives of about 10 percent of those affected and leaves about 2 percent as permanent carriers of the organism. Three-quarters of the world’s population live in areas where typhoid is endemic, and 1 out of every 300 of the world’s population contracts the disease each year. One million persons die of it annually, mostly children.

A variant illness, called paratyphoid fever, has many of the same features as typhoid fever, but is caused by members of the Salmonella bacterial family other than S. typhi. Typhoid and paratyphoid fevers are sometimes lumped together under the term enteric fever.

Etiology

The microorganism responsible for typhoid fever is a member of one of the largest and most widespread families of bacteria on Earth with over 1,700 serotypes recognized. The salmonellae are rod-shaped bacteria that have a cell wall and flagella, which give the bacterium motility.

Salmonellae can colonize the gastrointestinal tract of a broad range of animal hosts including mammals, birds, reptiles, amphibians, fish, and insects. Some types of salmonellae are highly adapted to specific animals; others have a wide range of hosts. Because of this versatility and the enormous consequent animal reservoir, the eradication of all salmonellosis would be essentially impossible.