from Part VIII - Major Human Diseases Past and Present
Published online by Cambridge University Press: 28 March 2008
Bacteria from several genera, including Campylobacter, Salmonelle, and Yersinia, as well as some strains of the common intestinal bacillus Escherichia coli, can invade the mucosa of the large intestine and cause dysentery, but members of the genus Shigella are by far the most important agents. Shigellosis is a common disease that occurs worldwide and afflicts persons of all races and age groups. In addition, Campylobacter appears to be an emerging pathogen, at least in the United States. It lives in the small intestine and produces a dysentery-like condition that is usually self-limiting.
Etiology and Epidemiology
Four species or subgroups of Shigella cause human disease. Shigella dysenteriae (subgroup A), the first to be discovered, is the most virulent. Shigella flexneri(B), Shigella boydii (C), and Shigella sonnei are less dangerous. More than 40 serotypes are recognized and are useful in tracing the spread of outbreaks.
Shigella organisms are passed in the feces and spread from person to person by the fecal-oral route. Bacteria are excreted during the illness and for about 4 weeks after recovery, but some asymptomatic individuals may act as carriers for a year or more. Contaminated food and water are the most common modes of transmission. Direct fecal contamination or mechanical carriage by flies can introduce bacteria into food, milk, or water. Sick, convalescent, or even healthy food handlers who have poor hygienic practices are especially dangerous; proper handwashing after defecation is a simple but effective preventive measure. Crowding and poor sanitation favor transmission, and outbreaks are common in jails and institutions for the retarded and mentally ill.
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