What is shigellosis?

Causes and Symptoms

Shigellosis accounts for half of the cases of bloody diarrhea in developing countries and a smaller portion of diarrheal illness in the United States. As of 2009, the World Health Organization reported 120 million cases and estimated that 1.1 million people die of the infection annually. Named after Kiyoshi Shiga, a Japanese scientist who performed much of the original research about it in the aftermath of an 1896 epidemic, Shigella is a gram-negative bacillus. The four species that cause shigellosis are S. dysenteriae, S. flexnerii, S. sonnei, and S. boydii.

The severity of shigellosis is quite variable, ranging from mild diarrhea to death. The more severe illness, dysentery, is characterized by abdominal cramps, tenesmus (a painful urge to defecate), and a bloody, mucus-filled diarrhea. Most victims of this severe illness are children, with those under age five years being particularly at risk with fatality rates around 25 percent. Poverty, malnutrition, poor hygiene, and overcrowding are associated with this serious disease, which is almost never seen in industrialized countries except in travelers who have visited an endemic area of the world. Shigella dysenteriae type 1 is responsible for most of these severe cases.

The pathogenicity (or disease-causing mechanism) of shigellosis is the invasion of the intestinal lining by the bacteria, causing inflammation and ulceration of the intestinal wall. Although Shigella
bacteria also produce a toxin, the role of this toxin in the infection is less clear and remains a research topic of much interest. In contrast to some other intestinal infections such as cholera, shigellosis produces a relatively small fluid volume loss, making dehydration less problematic. Victims also suffer from fever, malaise, and decreased appetite. Transmission of the Shigella bacteria is from person to person; there is no animal reservoir.

Treatment and Therapy

The diagnosis of shigellosis is made by the growth of Shigella in a stool culture. Antibiotic treatment is helpful, but resistance to many antibiotics is increasing. Quinolones, such as ciprofloxacin, are the treatment of choice for adults. Children are often treated with a cephalosporin or a variety of other agents. Azithromycin has been used successfully for multidrug resistant cases. Research continues on a possible vaccine.

Bibliography

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Humes, H. David, et al., eds. Kelley’s Essentials of Internal Medicine. 2d ed. Philadelphia: Lippincott Williams & Wilkins, 2001.

Kabir, Iqbal, et al. “Increased Height Gain of Children Fed a High-Protein Diet During Convalescence from Shigellosis.” Journal of Nutrition 128, no. 10 (October, 1998): 1688–1691.

Vorvick, Linda J. "Shigellosis." MedlinePlus, May 30, 2012.

World Health Organization. "Initiative for Vaccine Research (IVR): Diarrhoeal Diseases (Updated February 2009)." World Health Organization, February, 2009.