An electron micrograph of the cholera bacteria

Cholera 'in nature' proves to be more infectious

Cholera bacteria appear to become even more infectious as they pass through the human intestinal tractÑa finding that could help explain why the disease spreads so quickly in the Third World, according to a study published in the June 6 issue of Nature.

However, the discovery complicates efforts to develop a cholera vaccine because most research uses laboratory-grown strains of the bacteria that apparently are less infectious than those that have moved through a person, according to Dr. Andrew Camilli, assistant professor of molecular biology and microbiology at the School of Medicine.

"Growing bacteria in the laboratory does not reflect what's going on in nature," said Camilli, co-author of the study, who is working on developing a vaccine for the disease. But, he said, the research may help in identifying new targets for drugs designed to fight the disease.

Vibrio cholerae, waterborne bacteria, can cause severe and often-fatal diarrhea if lodged in sufficient numbers on the walls of the small intestine. The disease infects as many as 300,000 people in developing countries each year. Death by dehydration, sometimes within hours of infection, is now limited to about 1 percent of cholera victims, thanks to oral rehydration therapy. But pandemics of cholera continue. The most recentÑthe seventh pandemicÑbegan in 1961 and is still a threat in South Asia, Africa and Latin America.

Before the cholera bacteria leave an infected person, something prompts the germs to switch on a slew of genes, among them genes the bacteria need to move and to synthesize nutrients, Camilli said. Other genes that normally restrict the bacteria's movement are switched off, he said. These bacteria become more "hyper-infectious," or more easily capable of spreading to another person.

Material from the Associated Press was used in preparing this report.