Cholera's Genetic Code Revealed

From the WebMD Archives

Aug. 2, 2000 -- Researchers have unveiled the genetic code for Vibrio cholerae, the bacteria that causes cholera, paving the way for the discovery of new vaccines and drugs to combat the deadly disease. The discovery, which appears in the Aug. 3 issue of the scientific journal Nature, was announced Wednesday at a Washington press conference.

"We hope this data will help researchers to find new vaccine candidates and new drug targets for controlling this disease," John Heidelberg, PhD, the study's lead researcher, tells WebMD. "We're trying to make this available for the larger cholera community, to really help out with their research." Heidelberg is an assistant investigator at The Institute for Genomic Research in Rockville, Md.

Decoding the cholera genome also will help make cholera vaccines safer, according to the researchers.

The cholera discovery comes less than two months after the announcement that two organizations -- the federal government's National Human Genome Research Institute and Celera Genomics, a private company -- had each finished putting together the sequence of the human genome, or genetic code. That announcement, which was made at the White House in a ceremony overseen by President Clinton, has heightened interest in genomics, the study of genes and their functions.

Cholera is marked by severe diarrhea caused by consuming contaminated water or food. Most cases are found in developing nations, including parts of Africa and Asia. Person-to-person transmission is rare.

Although mild cases far outnumber severe cases, cholera can cause death from dehydration. According to the World Health Organization, more than 222,000 people worldwide contracted cholera between January 1999 and February 2000. Of those, more than 8,400 people died of the disease.

The standard medical treatment is the rapid replacement of lost body fluids and salts using a solution taken by mouth. When cholera occurs in an unprepared community, death rates may be as high as 50% -- either because there are no facilities for treatment or because treatment is given too late. If treatment is given early in the disease, the death rate is less than 1%.

Terri Beaty, PhD, professor of epidemiology at the Johns Hopkins University School of Public Health in Baltimore, says that knowing the cholera genome's size -- it's much smaller than the human genome -- and structure makes it much easier to develop treatments.

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Knowing the genome also could help researchers identify receptors within the cell, which could be targets for treatment, Beaty tells WebMD. "If the bacteria has a receptor that binds to a known human receptor, that could help scientists design a drug that would prevent it from binding so it might not be infectious," she says.

Even without the development of a vaccine, the research done so far on the cholera genome already has led to improvements in public health, according to Rita Colwell, PhD, director of the National Science Foundation. At the press conference, she explained how the discovery of the cholera genome confirmed that it attaches to small animals living in water. This led researchers to conduct a pilot project in Bangladesh in which female villagers who were gathering water filtered it through several layers of cloth. The incidence of cholera dropped dramatically as a result.

Because of that project's success, a larger study with 90,000 villagers is now under way, Colwell said.

 

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