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Last Updated: Sunday, 16 January, 2005, 00:19 GMT
Cholera understanding 'improved'
Cholera - Science Photo Library
Cholera is a water-borne disease
Scientists have developed a greater understanding of how cholera outbreaks spread.

Fears remain that the disease, which causes severe diarrhoea and can prove fatal if not treated, will take hold in the wake of the Asian tsunami.

Bangladeshi and US researchers said their work may help track and control such outbreaks.

The research is published in Proceedings of the National Academy of Science.

The most important strategies are to attempt to prevent cholera transmission by providing emergency clean water supplies, and a disease surveillance system
Dr Paul Shears, Liverpool School of Tropical Medicine

Cholera is an acute intestinal infection resulting in watery diarrhoea and is caused by the bacterium Vibrio cholerae.

It is particular problem in South Asia, where outbreaks usually occur twice a year, with the highest number of cases occurring immediately after the monsoon during September to December and a smaller increase between March and May.

Cholera is one of the diseases experts fear could spread in the wake of the tsunami because it is a water-borne disease.

Beneficial virus

Scientists had not understood what factors controlled the prevalence of the most harmful cholera bacteria.

The research team, from the International Centre for Diarrhoeal Disease Research in Dhaka and Harvard Medical School, carried out a three-year study to try to find the answer.

They discovered that the number of harmful cholera bacteria in water increased whenever the number of phages - a type of virus that uses a bacterial cell to multiply - decreased.

The phages are known to grow on, and kill, these harmful bacteria.

Cholera epidemics also appeared to end at the same time as large increases in the concentration of phages were found in the water.

The researchers suggest that phage concentration may be diluted during monsoon season, thereby triggering cholera outbreaks.

They add that monitoring the level of phages could be useful in tracking outbreaks, predicting epidemics and in anticipating emergence of new strains.

Field research

Dr Paul Shears, a consultant microbiologist at the Liverpool School of Tropical Medicine, said larger studies were needed before phages could be relied on as a way of monitoring cholera outbreaks.

"This is only one study from a limited area, and the results need to be treated with caution before being applied to other environments.

"In the meantime, the most important strategies are to attempt to prevent cholera transmission by providing emergency clean water supplies, and a disease surveillance system where there is early reporting of the first possible cases."

In the time of cholera
13 Sep 04 |  Health

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