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Last updated on April 16, 2014 at 1:21 EDT

Climate Change’s Effects On Spreading Plague

September 3, 2008

Scientists announced on Wednesday that previously unexplainable outbreaks of plague in the U.S. may be linked to climate change in the Pacific Ocean.

Scientists from Norway, The US and Sweden found that the number of infections in the US seemed to shift along with changing climate conditions known as the Pacific Decadal Oscillation (PDO).

The outbreaks seemed to occur during times of warm, wet conditions, authors wrote in the Royal Society journal Biology Letters.

The so-called “Black Death” is carried to humans by fleas living on rats. Scientists looked back and found that only 430 cases of the plague had been reported in the western US since 1950. The study focused on states west of a line running through North and South Dakota, Nebraska, Kansas, Oklahoma and Texas.

“The cases aren’t isolated. You can look at this phenomenon on a larger scale,” said Tamara Ben Ari, lead author of the study at the University of Oslo.

Fewer rodents die off in mild winters and food is more abundant in semi-arid areas when there is more rain.

But future climate change, stoked by human emissions of greenhouse gases, is likely to make the western United States drier, reducing the amount of food for rats. It is also projected to mean more heatwaves that can be deadly for fleas.

“Periods of high plague activity are likely to decrease in the western United States over the coming decades, especially in the active four corners region — New Mexico, Colorado, Arizona and Utah,” the study said.

However, experts say that global warming could actually facilitate the spread of the plague in parts of the world with a projected shift to moister conditions.

The World Health Organization says that nine countries reported 2,118 plague cases in 2003 and 182 deaths, with almost 99 percent of both cases and fatalities in Africa.

Image Caption: The Black Death plague is carried to humans by fleas living on rats. Scanning Electron Micrograph of a Flea Provided By CDC

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