EpidemicsSatellites could predict next cholera outbreak

With cholera making an unlikely resurgence, catching countries like Haiti and Pakistan by surprise, public health officials are exploring the potential for new technology to help stem the spread of future outbreaks.

The threat from cholera has been largely reduced, but the disease still poses a significant threat to many communities. Each year the disease affects three to five million people and claims more than 100,000 lives.

Most recently, cholera has begun to plague Haiti and Pakistan once more. The two countries had not seen a case of the disease in at least a century. Cholera causes extreme diarrhea and those infected face a 50 percent chance of death due to dehydration if they do not receive immediate treatment.

To combat cholera outbreaks, researchers believe that satellite images of the world’s oceans could help forecast when a cholera outbreak is likely to strike.

Shafiqul Islam, an environmental engineering and water diplomacy expert at Tufts University, and a team of scientists recently published a study in Water Resources Research that examines how large-scale environmental conditions can affect the initiation, transmission and propagation of cholera.

Islam’s team examined data from cholera outbreaks in Bangladesh’s Bengal Delta and found two annual peaks in cholera cases that occurred in the spring and fall. They found that the first spike seemed result from “low flow,” where long term drought conditions led to a mix of salt and fresh water off the Bangladeshi coast.

The bacteria that causes cholera thrives in these brackish conditions and can rapidly multiply in a few months. The bacteria’s growth is particularly quick if there is an algae bloom as zooplankton feeding on algae carry the bacteria. Once in the water, cholera can easily enter a coastal city through seafood or drinking water.

In the Bengal Delta, after the initial outbreak has begun to wane, heavy rains and flooding from the area’s monsoon season revives and spreads cholera inland. Areas with poor water and sewer systems are often hit the hardest.

Based on these findings, Islam believes that the conditions that lead to cholera outbreaks can be applied to areas beyond Bangladesh.

Using satellites to identify the chlorophyll laden phytoplankton in the Earth’s oceans, which zooplankton that carry the cholera bacteria feed on, researchers can develop prediction models that can forecast cholera outbreaks as far as two to three months in advance.

“If you want to make predictions, three days or even three weeks in advance is not enough,” Islam said. “You need at least two to three months in order to warn the public and allow professionals enough time to get ready.”

“If you can use this information to make a prediction, then you can mobilize the necessary resources,” he said.

As evidence Islam points to Haiti, which suffered a cholera outbreak following the devastating earthquake that struck the country in January 2010. More than 6 percent of those initially infected in Haiti eventually died from the disease. In contrast, only 0.1 percent of victims die in Bangladesh.

Islam says that if Haiti had a few months warning to prepare, the effect of the epidemic would have been far less severe as the effects of the disease can be mitigated with a simple solution of clean water with some sugar and salt.

Islam added that satellite monitoring will become even more crucial in the future as climate change models project increased drought and more severe flooding.

“If these models are correct, then cholera will get more intense,” he said.