Tropical Medicine: A Clinical Text, 8th Edition, Revised and Expanded

Bacterial and Rickettsial Diseases

Bacterial and Rickettsial Diseases Typhoid Fever Typhoid occurs worldwide but is much more prevalent in the tropics and subtropics. Typhoid and malaria are the two most common causes of fever in persons recently returned from a visit abroad. More than 90% of patients with typhoid in developed countries are infections imported from the tropics. The Organism Salmonella typhi is a gram negative, motile, rod-shaped bacteria with a flagellum. Unlike E. coli, which has a similar appearance, it does not ferment lactose. Tryptic broth or 10% Oxgall are used for culturing the organism from the blood, and selective Salmonella-Shigella medium (SS) is employed in culturing feces. After infection, antibodies are raised against three antigens: a somatic 0 lipopolysaccharide antigen, a flagellar H protein antigen, and a capsular Vi polysaccharide antigen. Pathology Infection is acquired by the ingestion of an adequate number of S. typhi, the chance of acquiring clinical typhoid being directly related to the number of organisms. Common vehicles of infection are contaminated water, milk, and food. Hypochlorhydric persons are at greater risk. The organisms penetrate small intestinal mucosal cells (the microfold or M cells), which overlie lymphatic aggregations (Peyer’s patches). They then multiply within the mononuclear cells of these aggregates and in related mesenteric lymph nodes. At a critical point, sufficient organisms are released into the blood to cause a bacteremia, and this PAGE 69 ................. 18086$ $CH5 07-15-11 13:49:11 PS 70 bacterial and rickettsial diseases coincides with the end of the incubation period. S. typhi are then carried to various tissues, especially of the liver, spleen, and lymph nodes, where they further multiply in macrophages. The gall bladder is invaded, and S. typhi reappear in the intestine and penetrate the mucosa. Hyperplasia within Peyer’s patches of the ileum may be followed by necrosis and sloughing. The resulting ulcers are found in the long axis of the bowel along the antimesenteric border. Hemorrhage and/or perforation may follow. There may be cloudy swelling and focal necrosis of hepatocytes; the spleen becomes enlarged, soft, and congested. Metastatic foci of infection may lead to abscess formation throughout the body. If the patient survives, eventual healing is usually complete without scarring. Clinical Features Incubation periods of 3 to 60 days have been reported but the average is 8 to 18 days. In ‘‘typical typhoid,’’ there is a step-like rise in temperature during the first week to 102F to 104F, accompanied by pronounced headache, malaise, and anorexia. Other symptoms include a sore throat, a dry cough, epistaxis, vague abdominal discomfort, and, frequently, constipation. The tongue is coated, and the pharynx may appear dry and inflamed. There is a relative bradycardia, especially when related to the temperature, and a relative leukopenia. During the second week, the temperature remains high, but now the pulse rate catches up. Abdominal symptoms become more definite, and there may be pain and tenderness in the right iliac fossa. The liver is often felt 2 to 3 cm below the costal margin, and the spleen becomes palpable as a soft, tender mass just below the left costal margin. Raised pink 2 to 5 mm macules (rose spots), which fade on pressure, occur in crops on the trunk. Toward the end of the second week and into the third week, the patient enters the most dangerous phase of the illness. Constipation may give place to ‘‘pea soup diarrhea.’’ A toxic encephalopathy may develop, the patient becoming confused or obtunded, lying immobile in bed, staring blankly although still rousable; other patients show agitation, disorientation, and delirium. Headache remains severe and may prevent sleep; meningismus is not uncommon. It is at this stage that hemorrhage and perforation most commonly occur. PAGE 70 ................. 18086$ $CH5 07-15-11 13:49:11 PS bacterial and rickettsial diseases 71 However, typhoid is more often ‘‘atypical’’ than ‘‘typical.’’ The fever may be high, low, or intermittent. The relative bradycardia is quite inconstant, and rose spots may be absent and are almost never found in those with dark skins. As in many fevers, dysuria is not uncommon and the white blood cell (WBC) may vary from 1,200 to 22,000 per mm3 . Typhoid in young children may be particularly ‘‘atypical,’’ commonly presenting with severe diarrhea, vomiting, dehydration, meningismus , and convulsions. While most pediatric typhoid cases will have a significant fever, even this feature may be missing in severely malnourished children and...