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Dysentery Bug Wields 'Sword and Shield'

Finding explains why people are so vulnerable to the diarrhea germ

FRIDAY, Feb. 25, 2005 (HealthDayNews) -- Scientists have discovered why the body's immune system puts up so little fight against the gastronintestinal scourge dysentery.

Dysentery, also known as shigellosis, is especially prevalent in the tropics and is caused by infection with the Shigella bacterium, usually through contaminated water or food. While the illness usually lasts no more than a week, longer-lasting episodes can lead to serious diarrhea and dehydration requiring hospitalization.

Reporting in the Feb. 24 issue of Science, British and French researchers found that Shigella infects cells by using a secretion system to inject its proteins into the human host cell -- much like a striking it with a chemical "sword."

At the same time, a layer of lipopolysaccharide protein on the surface of the bacteria acts as a "shield," protecting the organism from immune system destruction.

"This is the first description of bacteria able to use this 'sword and shield' approach," researcher Dr. Christoph Tang, of Imperial College London, said in a prepared statement.

Tang said the discovery "greatly expands our understanding of how bacteria are sometimes able to evolve, although it is unlikely to result in new treatments or vaccines for dysentery. In this case, the dysentery bacteria has evolved into a highly effective and dangerous infection."

More information

To learn more about dysentery, head to the U.S. Centers for Disease Control and Prevention.

SOURCES: Imperial College London, news release, Feb. 24, 2005
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