S. Typhi causes typhoid fever, while S. Paratyphi A, Salmonella Schottmuelleri (formerly S. Paratyphi B), and Salmonella Hirschfeldii (formerly S. Paratyphi C) cause a mild form of this disease referred to as paratyphoid fever. The term enteric fever includes both typhoid and paratyphoid fever caused by these Salmonella spp.
Enteric fever is generally an acute illness manifested by fever, headache, and abdominal symptoms. The incubation period is usually from 7 to 14 days, but may range from 3 to 56 days.
Onset of the disease is usually gradual, with headache, mal-aise, anorexia, a coated tongue, and abdominal discomfort with either constipation or diarrhea. A step-ladder pyrexia with rela-tive bradycardia and toxemia is the typical feature. The condi-tion is associated with a soft, palpable spleen and an enlarged liver. These symptoms are present for a week or more and are followed by gastrointestinal symptoms. This phase corresponds to an initial bacteremic phase, which is followed by coloniza-tion of gallbladder and then reinfection of the intestines.
Intestinal perforation, severe hemorrhage, and circulatory collapse are most important complications. Toxic encephalop-athy, cerebral thrombosis, hepatitis, pancreatitis, arthritis, and myocarditis are other complications. Convalescence is slow.
Relapse is common after initial recovery in 10–20% of patients treated with antibiotics. A relapse typically occurs approximately 1 week after the therapy is discontinued, but relapse even after 2 months has been reported. A relapse gener-ally is milder and shorter than the initial disease. Rarely, second or even third relapses may occur. The blood culture and serum H, O, and Vi antibodies are again positive in cases of relapse.
Paratyphoid fever caused by S. Paratyphi A and B resembles typhoid fever but is generally milder. S. Paratyphi C may also cause paratyphoid fever, but more often it leads to a frank septicemia with suppurative complications.