Shigella

Agricultural Disaster Preparedness and Recovery, Food Safety November 21, 2011|Print

Shigella

This micrograph reveals the first stage of shigellosis as it progresses; by this stage, the Shigella sp. bacteria have penetrated the intestinal mucosa. Image courtesy of CDC/ Dr. Sam Formal, Walter Reed Army Institute of Research.


Shigella are Gram-negative, non-motile, non-sporeforming, rod-shaped bacteria capable of causing disease in humans. Disease occurs when virulent Shigella organisms are consumed and invade the intestinal mucosa, resulting in tissue destruction. Some Shigella strains produce enterotoxin and Shiga-toxin (very much like the verotoxin of E. coli O157:H7). Shigella poisoning, also known as "shigellosis," is typically self-limiting, treatable, and most people recover quickly.

Causes of Shigellosis

Shigellosis is an infectious disease caused by bacteria of the genus Shigella, characterized by sudden and severe diarrhea (gastroenteritis or bacillary dysentery) in humans. Shigella thrives in the human intestine and is commonly spread through both food and person-to-person contact. Some persons who are infected may show no symptoms at all but still may pass the Shigella organism to others (carriers). Shigellosis is the third most common foodborne bacterial illness (about 30 percent less common than Salmonella and 20 percent less than Campylobacter).

Transmission

Shigellosis is principally a disease of humans and primates, such as monkeys and chimpanzees. The organism frequently is found in water polluted with human feces. Shigella cells must be swallowed to cause the disease. The disease often is spread when people fail to wash their hands with soap and water after using the restroom or changing a diaper. People who get Shigella on their hands can infect themselves by eating, smoking, or otherwise directly or indirectly touching their mouths. They also can spread the germs to anything they touch, potentially making others sick. In rare cases, swimming water in ponds, lakes, and pools also can spread Shigella if not properly treated and if enough water is swallowed. Such contamination may originate from sewage leaks and infected swimmers (particularly if they have or recently have had diarrhea).

Long-Term Effects of Shigellosis

Up to 3 percent of persons who are infected with Shigella later may develop chronic joint pain, swelling and irritation of the eyes, and sometimes painful urination. This is a reaction to the previous gastroenteritis and is called "reactive arthritis," or Reiter's Syndrome. It is a rare autoimmune disease that can occur after a bout of gastroenteritis from Salmonella or Shigella.

Foods Commonly Associated with Shigella

Although the majority of illnesses associated with Shigella are waterborne, approximately 20 percent have been linked to food (an estimated 80,000 cases per year). A wide variety of foods may be infected with Shigella. Some foods that have been identified in Shigella outbreaks include salads (potato, shrimp, tuna, chicken, turkey, macaroni, fruit, and lettuce), chopped turkey, rice balls, beans, pudding, strawberries, spinach, raw oysters, luncheon meat, and milk. Contamination of these or other foods is through the fecal-oral route. This means the food has been contaminated through unsanitary water or handling. It is possible for any food that has been mishandled to become contaminated and spread the disease.

Preventing Shigellosis

Unfortunately, there is no vaccine to prevent shigellosis. There are several things you can do help prevent the disease.

  • Wash hands frequently, especially after using the restroom.
  • Do not prepare food for others if you have been diagnosed with shigellosis.
  • Do not prepare food for others if you have diarrhea.
  • Control flies in the food preparation area.

Additional Resources

Food Related Illness and Death in the United States

Ohio State University Extension Fact Sheet

University of Florida Extension