New insight into predicting cholera epidemics in the Bengal Delta

November 04, 2009

MEDFORD/SOMERVILLE, Mass. - Cholera, an acute diarrheal disease caused by the bacterium Vibrio cholerae, has reemerged as a global killer. Outbreaks typically occur once a year in Africa and Latin America. But in Bangladesh the epidemics occur twice a year - in the spring and again in the fall.

Scientists have tried, without much success, to determine the cause of these unique dual outbreaks - and advance early detection and prevention efforts - by analyzing such variables as precipitation, water temperature, fecal contamination and coastal salinity. Now, researchers from Tufts University, led by Professor of Civil and Environmental Engineering Shafiqul Islam, have proposed a link between cholera and fluctuating water levels in the region's three principal rivers - the Ganges, Brahmaputra and Meghna.

"What we are establishing is a way to predict cholera outbreaks two to three months in advance," says Islam, who also holds an appointment as professor of water and diplomacy at The Fletcher School at Tufts. "It's not a microbiological explanation. The key is the river discharge and regional climate."

The Tufts researchers' findings were reported in the latest issue of Geophysical Research Letters, published October 10, 2009.

Understanding cholera's environmental catalysts

Vibrio cholerae lives and thrives among phytoplankton and zooplankton in brackish estuaries where rivers come into contact with the sea. The Bengal Delta, which scientists have considered the native land of cholera, is fed by three rivers.

Almost all of the rainfall in the region occurs during the four-month monsoon season between June and September. Water levels in the river system rise, causing floods that cover 20 percent of the land in an average year. Water levels then fall rapidly, though low-lying, depressed areas remain submerged for weeks.

The Tufts team tracked the month-by-month incidence of cholera using data from the International Center for Diarrhoeal Disease Research, a treatment center that recorded incidences of cholera for the biggest population center of Bangladesh from 1980 to 2000.

The Tufts team correlated these cholera incidence statistics with an analysis of water discharges from the three rivers. Their findings suggested two distinctive epidemic patterns that are associated with the seasonal cycles of low river flows and floods.

A spring outbreak occurs in March, during the period of low river flow in Bangladesh. The low river flow allows seawater from the Bay of Bengal to move inland, transporting bacteria-carrying plankton.

A second epidemic occurs in September and October, after monsoon rains have raised water levels. Here, a different dynamic takes place. Floodwaters have mixed water from sewers, reservoirs and rivers. As the floods recede, contamination is left behind..

Predicting cholera before it happens

Islam and his team linked the incidence of cholera cases to the level of water flow in the rivers. In order to confirm their findings, the researchers looked for a consistent pattern. They analyzed the incidence of cholera in five years of severely low river flow from 1980 to 2000 and compared it with five years of average and below average river flow. The same analysis was done for extreme, average and below average floods to study the fall epidemic.

The researchers found a relationship between the magnitude of cholera outbreaks and the severity of the region's seasonal low river flow and floods. "The more severe the low river flow, the larger the spring epidemic," says Islam. "The same thing is true with flooding during the fall." Islam says that the findings will contribute to the development of systems to anticipate and predict cholera outbreaks based on the hydroclimate of the region.
-end-
This research was funded in part by the National Science Foundation and a National Institutes of Health Fellowship. Researchers included engineering doctoral students Ali S. Akanda and Antarpreet S. Jutla.

Akanda, A. S., A. S. Jutla, and S. Islam (2009), "Dual peak cholera transmission in Bengal Delta: A hydroclimatological explanation," Geophys. Res. Lett., 36, L19401, doi: 10.1029/2009GL039312.

Tufts University, located on three Massachusetts campuses in Boston, Medford/Somerville, and Grafton, and in Talloires, France, is recognized among the premier research universities in the United States. Tufts enjoys a global reputation for academic excellence and for the preparation of students as leaders in a wide range of professions. A growing number of innovative teaching and research initiatives span all Tufts campuses, and collaboration among the faculty and students in the undergraduate, graduate and professional programs across the university's schools is widely encouraged.

Tufts University School of Engineering is dedicated to educating the technological leaders of tomorrow. Located on Tufts' Medford/Somerville campus, the School of Engineering offers a rigorous engineering education in an environment characterized by the best blending of a liberal arts college atmosphere with the intellectual and technological resources of a world-class research university. Close collaboration with the School of Arts and Sciences and the university's extraordinary collection of excellent professional schools creates a wealth of educational and research opportunities. The School of Engineering's primary goal is to educate engineers committed to the innovative and ethical application of technology in the solution of societal problems. It also seeks to be a leader among peer institutions in targeted areas of interdisciplinary research and education that impact the well-being and sustainability of society, including bioengineering, sustainability and innovation in engineering education.

Tufts University

Related Cholera Articles from Brightsurf:

Potential cholera vaccine target discovered
Investigators at Massachusetts General Hospital analyzed antibodies recovered from humans who survived cholera.

Cause of 1990s Argentina cholera epidemic uncovered
The evolution of epidemic and endemic strains of the cholera-causing bacterium Vibrio cholerae in Argentina has been mapped in detail.

Microbiome confers resistance to cholera
Many parts of the world are in the midst of a deadly pandemic of cholera, an extreme form of watery diarrhea.

Cholera studies reveal mechanisms of biofilm formation and hyperinfectivity
Free-swimming cholera bacteria are much less infectious than bacteria in biofilms, aggregates of bacterial cells that form on surfaces.

Consuming cholera toxin counteracts age-associated obesity
Here the research team tested a safe and well-established microbe-based immune adjuvant to restore immune homeostasis and counteract inflammation-associated obesity in animal models.

The cholera bacterium can steal up to 150 genes in one go
EPFL scientists have discovered that predatory bacteria like the cholera pathogen can steal up to 150 genes in one go from their neighbors.

Research on cholera adds to understanding of the social life of bacteria
Strains of the bacterium Vibrio cholerae transform themselves from small, comma-shaped cells to long filaments in nutrient-poor environments to aid short-term survival.

The cholera bacterium's 3-in-1 toolkit for life in the ocean
The cholera bacterium uses a grappling hook-like appendage to take up DNA, bind to nutritious surfaces and recognize 'family' members, EPFL scientists have found.

Genetic code of WWI soldier's cholera mapped
The oldest publicly available strain of the cholera-causing bacterial species, Vibrio cholerae, has had its genetic code read for the first time.

Vaccine study confirms sensitivity of cholera test
Recently, the sensitivity of fecal microbiological cultures for detecting cholera has come under question.

Read More: Cholera News and Cholera Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.