Ocean Heat Can Predict Malaria Outbreaks in India

By Tim Radford, Climate News Network

Health officials may have a new way to anticipate malaria epidemics in north-west India. All they have to do is check the sea surface temperatures in the tropical south Atlantic, off the coast of western Africa.

If the water is colder than normal in July, then prepare for an epidemic of the Anopheles mosquito and its little Plasmodium parasite four months later in Kutch and the Thar Desert of India.

Research shows if the water is colder than normal in July, then prepare for an epidemic of the Anopheles mosquito and its little Plasmodium parasite four months later in Kutch and the Thar Desert of India.
Credit: Michael Day

Mercedes Pascual of the University of Michigan and colleagues report in Nature Climate Change that monsoon rainfall totals were a reasonable predictor of breeding sites in parts of India that are normally arid or semi-arid, but these offered no more than a month’s warning.

So she and her fellow scientists began looking for other possible correlations. Malaria was once all but eliminated in India: the disease began to return in the 1970s, and about 9 million cases are now recorded annually.

The north-west is at the margins of the range of the disease-bearing mosquito: periodically, outbreaks of malaria hit an unprepared population.

Pascual, a professor of ecology, analyzed the pattern of occurrence in north-west India, and with help from colleagues in London, Maryland, Spain and India began to look for possible climatic indicators that would give a better warning.

With help from statistical and computer climate models, they found that sea surface temperatures in the tropical South Atlantic proved to be a significant indicator of the rainfall to come in the Indian summer monsoon season, and thus of epidemics of malaria that peaked in October and November.

Time to spray

They counted epidemic outbreaks between 1985 and 2006, and found that July sea surface temperatures correlated with subsequent epidemics in nine of 11 malarial autumns; and 12 out of 15 non-epidemic years.

Scientists found that sea surface temperatures in the tropical South Atlantic proved to be a significant indicator of the rainfall to come in the Indian summer monsoon season, and thus of epidemics of malaria that peaked in October and November.
Credit: flickr/Andy Langager

It seemed to need only 0.5mm of rain a day during the monsoon in the north-west to leave pools of water where mosquitoes could breed.

The research has indirect implications for adaptation to global warming – the geographical range of malarial hazard is expected to increase with global temperatures – but is also an indicator of the exquisite interconnectedness of weather systems around the globe.

Above all, it could have important practical consequences: health chiefs in the region would have more time to prepare spraying programs to interrupt the mosquito’s breeding cycle, and to encourage vulnerable communities to use mosquito nets.

“The climate link we have uncovered can be used as an indicator of malaria risk. On the practical side, we hope these findings can be used as part of an early warning system,” Professor Pascual said.

Tim Radford is a reporter for Climate News Network. Climate News Network is a news service led by four veteran British environmental reporters and broadcasters. It delivers news and commentary about climate change for free to media outlets worldwide.