June 23, 1999

BIOTECH TOOL RINGS ALARM FOR CHOLERA

BALTIMORE, Md.--For the first time, the presence of cholera bacteria can be precisely and quickly identified anywhere in the world, thanks to a new detection tool from the University of Maryland Biotechnology Institute, (UMBI).

"Now we can certainly help countries reduce the number of cholera cases dramatically by detecting the bacteria early," says research associate professor Dr. Anwar Huq at UMBI’s Center for Marine Biotechnology, (COMB) in Baltimore.

The new tool could especially help developing countries to anticipate cholera outbreaks, said Huq. "It is best used in combination with a good vaccine and prevention measures such as alerting people not to drink untreated water that may contain large numbers of cholera bacteria."

The tool is a molecular probe that locates a precise portion of only the cholera bacteria. COMB microbiologists Dr. Johnsik Chin, Huq and team leader Dr. Rita Colwell (now director of the National Science Foundation) uncovered a sequence of the bacteria’s DNA that is unique and different from DNA of closely related bacteria. Previously, molecular biologists had difficulty in distinguishing DNA of a cholera bacterium, Vibrio cholerae from its close cousin Vibrio mimicus, reports Huq.

"The beauty of this highly specific probe is that any laboratory in the world can use it on a sample of sediment, water, plankton, or anything else containing the cholera bacteria that will reveal the DNA sequence," adds Huq. No longer will laboratories need to culture the actual cholera bacteria to know if they are present, he notes.

In COMB experiments, the researchers have used the probe to successfully detect cholera bacteria in the Chesapeake Bay, in Peru, the Gulf of Mexico, Bangladesh and in current research in India, says Colwell. "This is both an epidemiological tool (to define the potential or real extent of a cholera outbreak) and an ecology tool," she adds.

Colwell, who has been a leader of UMBI cholera research for 25 years, notes that outbreaks around the world are associated with changes in global climate. So far this year, there have been new outbreaks in Cambodia, Nigeria, Sudan, Somalia, Madagascar, Brazil, Congo, Somalia, Zambia, Kenya and Mozambique, according to the World Health Organization’s Division of Communicable Disease Surveillance and Response.

Huq reports that V. mimicus, can cause human food poisonings if people inadvertently eat it in uncooked fish, crabs, oysters or possibly in shrimp. But it does not cause severe epidemics. There have been numerous cholera false alarms in the past, he says, when laboratory researchers detected V. mimicus and assumed it was V. cholerae.

In contrast, V. cholerae can cause an acute intestinal infection. After a victim ingests the bacteria via contaminated water or seafood, there is an incubation period of less than one day to five days. It then produces a toxin that causes diarrhea and vomiting. It can quickly lead to severe dehydration and death if not treated promptly.

Huq said quick action by local authorities can prevent severe outbreaks by early detection of V. cholerae. He added that in Dhaka, Bangladesh in 1991 there were up to 4,000 to 5,000 new cases of cholera reported each week, figuring in a total of 4,000 fatalities for that year in that city alone.

In an effort to stem an apparent rising tide of cholera around the world, researchers at the

U. of Md. and Johns Hopkins University have been funded by about $5 million from the National Institutes of Health, the U.S. Environmental Protection Agency and the National Aeronautics and Space Administration. Teams of physicians, ecologists, epidemiologists, microbiologists, chemists, oceanographers, biostatisticians, sociologists, and remote sensing scientists, says Colwell, are assessing the ecology, epidemiology and the molecular biology of cholera.

Colwell reports the new detection tool, for example, will help scientists "to find out exactly how cholera occurs in Bangladesh. In the future, we will produce maps of epidemics from space, using remote sensing satellites, for not only cholera, but also for diseases such as malaria, cryptosporidium, hanta virus (the rodent-transmitted HPS respiratory disease), and dengue virus (which causes a mosquito-transmitted disease in tropical regions but spreading to sub-tropical countries including the United States).