SHIGELLOSIS

Shigellosis, also called bacillary dysentery, is caused by four species of Shigella bacteria: Shigella dysenteriae, Shigella flexneri, Shigella boydii and Shigella sonnei. The disease is caused when virulent Shigella organisms attach to, and penetrate epithelial cells of the intestinal mucosa. After invasion, they multiply intracellularly, and spread to contiguous epitheleal cells resulting in tissue destruction. Some strains produce enterotoxin and Shiga toxin (very much like the verotoxin of E.coli O157:H7).

Cause/ Food Sources
Drinking water contaminated with human faeces, public places such as swimming pools with poor hygienic conditions and contaminated foods are the major causes of the disease.
Approximately 20% of cases of shigellosis are transmitted via contaminated food or water. Generally, the food preparer is the individual who contaminates the food, but food may also become contaminated previously during processing. Contamination of drinking water by Shigella is a problem that generally only occurs in the developing world.
Salads (potato, tuna, shrimp, macaroni, and chicken), raw vegetables, milk and dairy products, and poultry are the associated foods with the illness. Contamination of these foods is usually through the fecal-oral route.

Detection
Determining that Shigella is the cause of an illness depends on laboratory tests that identify the bacteria in the stool of an infected person. Shigella is not a normal inhabitant in the colon, but the culture tests are sometimes falsely negative. This is because Shigella is somewhat difficult to isolate from a stool specimen because it has characteristics that are similar to normal colon bacteria.
Newer methods are being developed to identify foodborne pathogens, like Shigella, in food samples. These tests often work by locating segments of RNA unique to the organism.

Symptoms
Most people who are infected with Shigella develop diarrhea, fever, and abdominal cramps. Severity of the disease ranges from mild to very severe diarrhea. Diarrhea is bloody 25-50% of the time and most often contains mucus. Rectal spasms, medically termed "tenesmus," are common. The illness starts 12 hours to 6 days, usually 1-2 days, after exposure. Dehydration is also a common symptom of Shigella infection.

Treatment
Shigellosis can usually be treated with antibiotics. The antibiotics commonly used for treatment are ampicillin, trimethoprim/sulfamethoxazole, nalidixic acid, or ciprofloxacin. Appropriate treatment kills the Shigella bacteria that might be present in the patient's stools, and shortens the illness. Unfortunately, some Shigella bacteria have become resistant to antibiotics and using antibiotics to treat shigellosis can actually make the germs more resistant in the future.

Prevention

• Wash hands with soap carefully and frequently, especially after going to the bathroom, after changing diapers, and before preparing foods or beverages
• Keep children with diarrhea out of child care settings
• At swimming pools, maintaining a chlorine level of at least 0.5-PPM will kill Shigella.
• At swimming beaches, having enough bathrooms near the swimming area helps keep the water from becoming contaminated.
• People with diarrheal illness should not prepare food for others
• Basic food safety precautions will also help to prevent shigellosis. Shigella organisms are killed by heat used in cooking.
• Drink water only if it has been chlorinated (most tap water) or treated with ozone (most bottled water) and then you know it will not contain pathogenic bacteria..
• Consume only pasteurized/sterilized dairy products
• Simple precautions taken while traveling to the developing world can also prevent getting shigellosis: "boil it, cook it, peel it, or forget it".
• Drink beverages only if they are canned/bottled or boiled (like coffee) in a sanitary environment.
• Do not use ice in beverages. 

Reference
http://www.hpa.org.uk/infections/topics_az/shigella/menu.htm
http://www.cfsan.fda.gov/~mow/chap19.html
http://www.about-shigella.com/
http://www.cdc.gov/ncidod/DBMD/diseaseinfo/shigellosis_g.htm

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