11 December 2007

Climate change ups malaria

As the temperature rises, conditions become favourable for mosquito breeding, and malaria outbreaks occur at higher altitudes than before.

In one New Guinea hilltop village the message was rooted deep in lore: If you hunt in the valley below and sleep there overnight, evil spirits will possess you, you'll become sick, and you'll die.

It was a homespun kind of malaria control in the highlands of this western Pacific island, long free of the disease-bearing mosquitoes that plague the hot and humid nights of its lowlands, said Dr Ivo Mueller, a lead scientist at the Papua New Guinea Institute of Medical Research.

As the Earth warms, however, "malaria epidemics in the highlands are now basically happening every year," Mueller said.

The threat of collapsing ice sheets and super-hurricanes dominates many discussions at the annual UN climate conference now under way in Bali, Indonesia. On the litany of ills linked to climate change, the slow spread of warm-weather diseases is more a quiet scourge, one whose ultimate cost remains incalculable.

Burden on healthcare
"What is going to be the burden on the healthcare infrastructure of poor, developing countries?" asked Hannah Reid, of London's International Institute for Environment and Development, opening a panel session on the health impacts of climate change.

Forecasting those impacts can be controversial, both politically and scientifically.

In Washington this October, for example, The Associated Press reported that the Bush administration, which opposes mandatory international action to rein in warming, expurgated pages discussing such negative health effects from a US official's congressional testimony.

At the technical level, researchers in poorer nations like Papua New Guinea often cannot find the reliable health statistics - or, sometimes, historical temperature readings - they need to reach scientific conclusions.

"Not having quality health data that spans many decades makes the long-term assessment of climate change impact on health rather difficult," Dr Jonathan Patz, an international expert on health and climate, said in a telephone interview from his office at the University of Wisconsin.

Mueller's team, based in the highlands town of Goroka, faces that problem.

Temperature has risen
"Whether this is already climate change - it's difficult to say because we don't have time-series data," Mueller said. "There's no reliable malaria data from the late 1970s to 2000. But we do know that in the last 20 years temperatures have risen 0.6 to 0.7 degrees Celsius in the highlands."

And they know they're seeing more malaria at higher altitudes. One statistical glimpse: In 2005 the World Health Organization said reported malaria cases in Papua New Guinea's Western Highlands province rose to 4,986 in 2003 from 638 in 2000 - considered minimum figures in view of reporting deficiencies.

Two out of five Papua New Guineans live in the lush, densely populated highlands of the equatorial country, most between the altitudes of 1,500 meters and 2,000 meters (5,000 and 6,700 feet), "where there's no malaria or low epidemic outbreaks," Mueller said.

"There's talk of a 2- or 3-degree temperature rise in the future," he said. If so, "perhaps 2 million people would go from a low- or no-risk area to considerable risk."

International health authorities say more than 1 million people, mostly African children, die each year of malaria, caused by a parasite transmitted by the bite of the female anopheles mosquito. Tens of millions more suffer chronically from the debilitating disease.

More heat, more mosquitoes
The parasite needs temperatures above 17 degrees Celsius to develop. As for the "vector," the mosquito, scientists have found that even small temperature increases can produce disproportionately large increases in mosquito populations.

The Intergovernmental Panel on Climate Change, a U.N. network of climate scientists, has long projected that mosquito-borne tropical diseases would spread to new areas that grew warmer. But in its latest reports, issued this year, the IPCC panel was cautious about more specific projections.

"Despite the known causal links between climate and malaria transmission dynamics, there is still much uncertainty about the potential impact of climate change on malaria at local and global scales," it concluded. Malaria's range may even contract in such areas as the Amazon, which is expected to grow drier as the world warms, scientists say.

As Mueller noted, factors beyond temperature and humidity can influence malaria's spread: population movements, deforestation, preventive health measures and failing health systems, among other elements.

But the malaria researcher said the bottom line is clear.

"There's no question," he said. "If you put climate change into the equation and the climate becomes more favourable, the mosquitoes' numbers go up and you're going to have more and more transmission." The evidence lies not only in New Guinea. Similar highlands epidemics have been reported in previously malaria-free areas of east Africa, Madagascar and West Papua, on the western Indonesian half of this island. – (Sapa)

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Malaria Centre

December 2007


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