A recent examination of the world's largest river basins found nutrient-rich and powerful river discharges led to spikes in the blooms of plankton associated with cholera outbreaks.
The findings will help give public health authorities another critical clue toward predicting future outbreaks of cholera. The study's lead investigator, Shafiqul Islam, spoke to allAfrica's Ellie Schneidman about the research. Islam is a professor in the Department of Water Diplomacy at the Fletcher School of Law and Diplomacy and in the Department of Civil and Environmental Engineering at Tufts University in the United States.
You have said, "The main significance [of the study] 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." Can you further explain this and the relevance to previous studies?
There was an article published in 2000 stating people have found some correlation between sea surface temperature and cholera outbreaks. That was used as evidence. Really, if the temperature goes up then the cholera goes up, but it is a problem because if the sea surface temperature goes up phytoplankton goes down. If the phytoplankton goes down, then the cholera should go down. We asked, 'Why is this happening?'
Then what we questioned really was the casual mechanism because it wasn't understood. In the Bengal region we see a positive relationship between sea surface temperature and cholera, not because they're linked but because we have a lot of water coming from the large rivers and bringing a lot of nutrients. What you find in most of the basin is that the relationship of phytoplankton and sea surface temperature is inverse, meaning that when temperature goes up, phytoplankton goes down, if phytoplankton goes down then cholera goes down.
How does this study differ or contradict earlier studies?
It offers a different explanation. What we observed in the Ganges basin is the sea surface temperature and phytoplankton are positively related, but that relationship has nothing to do with the actual dynamic. The dynamic has to do with the water bringing a lot of nutrients. If you're very close to the coast, then the sea surface temperature and the phytoplankton are positively related, but if you are further away, they are negatively correlated because when you go farther away from the coast, the ocean dynamic takes over. To prove this we have gone to other places - the Amazon, Congo and Orinoco [rivers] - all finding the same thing.
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What does the study mean for the battle against cholera?
What it means, essentially, is we need to find out a better way to make a prediction for cholera at least one to two months in advance. To do this we need a better prediction of the river or phytoplankton. We're trying to develop an early cholera warning system. Those systems should have a lead-time of one to two months so that when the cholera hits in an area we can start preparing.
How do you see the current cholera outbreak in the Democratic Republic of Congo ending?
Once cholera starts there are two things that need to happen. First we need to find out where the next cholera outbreak will happen so we can quarantine it. And once it starts you can use treatment, you can use a vaccine. Over the seasonal changes it will go into hiding because it cannot survive in colder temperatures. It will die down a little. But cholera in the Congo - what they have there is a seasonal cycle and that seasonal cycle is very strongly linked with the water cycle.
Is there anything else you would like to add?
Essentially, we need to find a large-scale climate variable so we are able to build up an early warning system. An early warning system allows public officials to get ready for the next outbreak so we can save lives.
