One mystery resolved on cholera by examination of four major river basins – including the Ganges, Brahmaputra, Meghna, Congo, Amazon and Orinoco in South America – finds when water flow rose, nutrients in the water were associated with increase in cholera cases
Published on August 3rd in the American Journal of Tropical Medicine and Hygiene – A new study revealed, an investigation of the biggest river basins in the world discovered, nutrient-rich and powerful discharges led to spikes in the blooms of plankton linked with cholera outbreaks. These raised discharges frequently take place at times when coastal water temperature is increased, implying that it will be more complicated than first believed in predicting global warming’s potential temperature effect on cholera.
These findings will help give public health authorities another essential clue in predicting outbreaks in the future of cholera, based on climatic and environmental models, in the aspiration of stopping the expansion of the lethal and highly infectious disease that presently curses Haiti and several other countries.
The researchers started in the Bay of Bengal, where their goal was to solve a puzzle : When sea temperatures rise, phytoplankton – microscopic plants in the ocean that provide a food source for zooplankton, which cholera bacteria are linked with – decreases. So why did previous investigations find sea temperatures rising and numbers of phytoplankton also increasing? They analyzed twelve years of data, together with images from NASA satellites, and highlighted the large flows from the Ganges, Brahmaputra and Meghna rivers, transporting nutrients from soil as the reason for bloom in phytoplankton, followed by zooplankton which contributes to outbreaks of cholera.
Shafiqul Islam, PhD, the lead researcher of the study, a professor in the Department of Civil and Environmental Engineering and at the Fletcher School of Law and Diplomacy at Tufts University in Medford/Somerville, Massachusetts, says,
“We weren’t satisfied with just this result, so we then went to test this finding in other places – the Orinoco (in South America), the Congo, and the Amazon river basins, and we found the same thing: The positive relationship between phytoplankton blooms and ocean temperature is related to large river discharges.
The main significance is that finding an association between sea surface temperatures and cholera outbreaks should not lead us to conclude that with global warming, cholera will definitely go up.”
Islam said however, that global warming might play a role in alternative ways in outbreaks of cholera,
together with contributing to droughts and high salinity intrusion in the dry season and floods in the wet season. Published recently in the journal Water Resources, both of those conditions have been discovered to also contribute to cholera epidemics.
“If river flows are more turbulent, if droughts are more severe, if flood is more severe, cholera is more severe, but cholera may not have direct linkage with rising sea surface temperatures.”
Bacterium Vibrio cholerae, which produces a toxin that causes severe diarrhea, is the cause of Cholera. Most common in areas with poor sanitation, crowding, and social instability, Cholera creates extreme fear due to the sudden onset of diarrhea with the potential for a high number of deaths.
Nine months ago in the Democratic Republic of Congo, a furious cholera outbreak has killed hundreds and sickened over 100,000 people, the World Health Organization reported in July. Since the rainy season started this spring, Haiti is seeing a new upsurge in cholera cases. Beginning in October 2010 the epidemic has caused illness in over 300,000 people, killing nearly 5,000.
Rita R. Colwell, PhD, co-author of the investigation and a professor at both the University of Maryland and the John Hopkins Bloomberg School of Public Health explained,
“We don’t know for sure if Haiti’s cholera outbreak is related to its river system, but its rivers were severely impacted by the earthquake, It’s a system we should study in Haiti. I’m intrigued to see this relationship between cholera and river flow. It gives us much more detail about what can trigger cholera outbreak.”
Peter J Hotez, MD, PhD, President, American Society of Tropical Medicine and Hygiene said the investigation underscored the “complex ecology associated with cholera,” adding that researchers work is understanding cholera outbreaks is critically important now.
“Cholera seems to be gaining a foothold in more places than it used to be. We used to see shorter outbreaks, but in Africa, and now in Haiti, we’re seeing nationwide epidemics lasting months or more than a year. We obviously need to be taking a different approach.”