Shigella - diarrhea that kills 

Shigella are the most important organisms causing dysentery, and dysentery may be simply defined as diarrhea containing blood. 

The Shiga bacillus, called Sd1, is the most virulent of the four serogroups of shigella. Sd1 is the only cause of epidemic dysentery. In addition to bloody diarrhea, the illness caused by Sd1 often includes abdominal cramps, fever and rectal pain. Approximately 5-15% of Sd1 cases are fatal.

Shigella Sd1 has caused epidemics of dysentery throughout the world. It caused a 4-year epidemic in Central America beginning in 1968 that resulted in more than 500 000 cases and at least 20 000 deaths. No epidemics have occurred in the region since then, but Sd1 continues to occur sporadically in the Western hemisphere. In Africa, epidemic dysentery due to Sd1 appeared in eastern Zaire in 1979 and has subsequently been confirmed in Angola, Burundi, Equatorial Guinea, Ethiopia, Kenya, Malawi, Mozambique, Rwanda, Sao Tome and Principe, South Africa, Swaziland, Tanzania, Uganda, Zambia, and Zimbabwe. The latest outbreaks have been in Guinea (small scale) and Sierra Leone (on a threatening, much larger scale) in 2000.

Four main species of shigella are able to cause diarrheal diseases. The symptoms of shigellosis include diarrhea and/or dysentery with frequent (not systematically) bloody stools and abdominal cramps. Shigella infections are more severe in children who are malnourished and have a greater adverse effect on nutritional status than do other infections that cause watery diarrhea. 

Globally, shigella infections cause an estimated 600. 000 deaths per year, mainly in developing countries with unsafe water supplies. 

Transmission
Transmission usually occurs via contaminated food and water, or through person-to-person contact. The bacteria are highly infectious by the oral route. However, few studies have been done to determine how dysentery is spread. Epidemics of shigella Sd1 usually occur in impoverished areas. They affect people of all ages, with the highest age-specific incidence occurring among adults and the highest case fatality rates occurring among children.

Children and diarrheal diseases in Africa
In Sub-Saharan Africa, diarrheal diseases are still a leading cause of mortality and morbidity in children under five years of age. It is estimated that each child in the region has five episodes of diarrhea per year and that 800,000 die each year from diarrhea and dehydration. Undernutrition and measles are very commonly associated with this mortality. 

The prevention of diarrhea ultimately depends on the improvement of water supplies and sanitation, which are very expensive but will eventually occur. 

The prevention of death from dehydration arising from diarrhea is straightforward, using cheap oral rehydration salts or simple home-made fluids. Since 1992, Sub-Saharan Africa has been facing a severe epidemic of shigella dysentery. The bacteria causing this epidemic are rapidly developing resistance to the first line antibiotics normally used for treatment. The second line treatment is very expensive. In addition to killing children directly, dysentery is a common cause of persistent diarrhea, which is responsible for 15% of deaths from diarrhea in children.

Treatment
Usually diarrhea due to shigella are effectively treated by a 5-day cure basic antibiotic medicines. During an epidemic, all shigella patients should receive an antibiotic to which Sd1 from local cases has been shown to be sensitive, WHO instructions say. Dehydration should be treated with oral rehydration salts or, if severe, with intravenous fluids. Urgent efforts should be made to obtain enough antimicrobials to treat all patients, but if in short supply they should be reserved for those at highest risk of secondary complications and death. These would include children under five years of age, adults older than 50 years, patients presenting with dehydration, and those with serious underlying conditions such as malnutrition. 

However, in several areas of the world, shigella is resistant to available and affordable antibiotics. In one central African country the bacillus was resistant to all oral antibiotics that were locally available. Furthermore, shigella Sd1 can quickly develop resistance. Antibiotics are often effective against it for only one or two years after being introduced; resistance has even been observed to develop during the course of an epidemic. As resistance to commonly available antibiotics becomes more prevalent, alternative antibiotics are needed which are more expensive and more difficult to procure.

No vaccines against shigella infection currently exist. However, different vaccine candidates are under development, and there is much research on this field. 

Prevention
The recommendations for prevention against shigella are those given for all diarrheal diseases due to bacteria. Prevention of these enteric diseases comprises basic sanitary and hygiene measures including purifying water supplies, improving water delivery and sewage control, supplying handwashing facilities, latrines, boiling water and supervising foodhandlers. 

The WHO in general recommends that health education efforts should promote improved personal, domestic, and environmental hygiene. This includes hand washing with soap after defecation and before handling food, use of clean drinking water, safe practices for preparing and storing food, and safe disposal of faeces.

More information
The publication AGuidelines for the control of epidemics due to Shigella dysenteriae type 1 is available from the Distribution and Sales Unit, of WHO. See also the website of the WHO (use the search engine to search for shigella).

Source: WHO

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