Profiling Shigella

Four species of bacteria belong to the genus Shigella – S. boydii, S. dysenteriae, S. flexneri and S. sonnei. All of them are pathogenic.

Some history

Shigella dysenteriae – the species that causes dysentery – was the first Shigella species to be described. It was isolated for the first time from a sample of feces during the investigation of a case of dysentery in 1888.

What is Shigella, and where is its natural habitat?

Shigella causes gastrointestinal infections, including dysentery. Members of this genus produce a toxin known as shiga toxin – similar to the toxin produced by E. coli O157:H7 and other shiga-toxin producing strains of E. coli. Shigella‘s natural habitat is the intestinal tract of humans and primates. Shigella dysenteriae remains the most common of the four species in underdeveloped countries; S. sonnei and S. flexneri are the dominant species in the industrialized world.

How is Shigella transmitted? What is the incubation period of the infection?

Shigella is not typically found in the soil. The disease is transmitted through consuming contaminated food or water (which has been exposed to fecal material that contains Shigella), and by direct or indirect person-to-person contact. Swimming in contaminated water also can be a mode of transmission. The incubation period typically is 24-48 hours.

What illnesses are caused by Shigella? How long does it take to develop?

Depending on the species, an individual infected with Shigella may develop either dysentery or shigellosis, approximately 24-48 hours after becoming infected.

What are the symptoms of Shigella dysentery and shigellosis

Dysentery:- Individuals infected with Shigella dysenteriae will likely suffer from abdominal cramps and frequent, bloody diarrheic stools that also contain mucus.

Shigellosis:- A milder form of illness, characterized by abdominal cramps, fever and diarrhea – sometimes bloody or containing mucus – lasting 4 to 7 days.

What is the prognosis of Shigella infections?

The disease is largely self-limiting in the developed world. Complications that may develop include severe dehydration, Reiter’s syndrome (a form of reactive arthritis) or hemolytic uremic syndrome. In underdeveloped and emerging countries, where malnutrition and poor health are common, shigellosis and dysentery often can be fatal.

What foods carry Shigella?

Food and water may become infected through direct or indirect contact with fecal material from an infected individual.

How can susceptible people protect themselves from infection?

The US Centers for Disease Control and Prevention (CDC) offers the following advice for preventing the spread of Shigella:

• Wash hands with soap carefully and frequently, especially after going to the bathroom, after changing diapers, and before preparing foods or beverages.
• Dispose of soiled diapers properly
• Disinfect diaper changing areas after using them.
• Keep children with diarrhea out of child care settings.
• Supervise hand washing of toddlers and small children after they use the toilet.
• Do not prepare food for others while ill with diarrhea
• Avoid swallowing water from ponds, lakes, or untreated pools.

For more information on Shigella and other food-borne pathogens, visit the CDC website or read Food Safety: Old Habits, New Perspectives.