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Dengue Fever Slips Across the Border

• November 16, 2009 • 3:10 PM

In a less remarked-upon aspect of climate change, tropical diseases like dengue fever — once restricted to warmer or moister climes — are infiltrating the United States.

Stories of the potential consequences of climate change have been used to motivate politicians, shame deniers and educate the broader public on how an abstract scientific concept could breed concrete disasters. There are, of course, the rising sea levels and warmer temperatures, migrating species and shrinking ice caps.

Less frequently cited, it turns out, is another concern: dengue fever.

Public health experts now warn that climate change could come with a host of complications that have seldom figured prominently in all the talk of emissions reductions and treaty negotiations. More obvious among the concerns — both in sanitation-poor Third World countries and in the U.S. — are heat-related strokes or deaths. Respiratory illnesses like asthma are another likely consequence of continued air pollution.

But a report recently released by the United States Global Change Research Program also warned of the possible increase in waterborne pathogens and diseases carried by insects and rodents.

Vector-borne diseases like malaria, the plague and dengue fever thrive in tropical parts of Africa where the fleas, ticks and mosquitoes that transmit them live. Malaria, for example, ceases to be a threat in the Sahara where there isn’t enough water for the mosquitoes to survive.

The risk of such diseases is directly related to temperature and precipitation levels — meaning as temperatures rise or rainfall patterns change with the changing climate, existing diseases (or the mosquitoes that carry them) may be on the move, too.

The problem isn’t limited to Africa. In Mexico, since 2001, there has been a 600 percent increase in cases of dengue hemorrhagic fever, according to Mary Hayden, a scientist with the National Center for Atmospheric Research. As part of a briefing on the health implications of climate change in a Senate office building on Capitol Hill today, Hayden played a brief video illustrating the dramatic spread through the Americas of dengue cases reported to the World Health Organization since the 1960s.

In 2005, the first case was documented in the continental United States along the Texas-Mexico border.

“Dengue is definitely on the move,” Hayden said, “and it’s moving northward.”

It’s also moving toward physicians who aren’t trained to recognize it. As recently as September, a surprising outbreak occurred in Key West, Fla.

In another illustration of the relationship between unusual weather patterns and deadly diseases, Rita Colwell, a former director of the National Science Foundation and now a professor at the University of Maryland and Johns Hopkins University, recalled a hantavirus outbreak in the American Southwest in the early 1990s. Heavy rainfall from the 1991-92 El Niño led to a dramatic increase in deer mice populations in the Four Corners area. Researchers later traced the simultaneous outbreak of a deadly disease – once thought to be the result of bioterrorism – to the mice who carried the hantavirus.

Addressing climate change with public health consequences in mind — the motive of Monday’s congressionally targeted event — does present a kind of paradox. The energy use associated with causing climate change in countries like the U.S. is also partly responsible for improvements in sanitation and health that have made diseases like cholera and the plague antiquated concerns in the West.

“At a certain point, using more energy is associated with improvements in health, longer life expectancy, lower infant mortality,” said Lynn Goldman, a professor of environmental health sciences at Johns Hopkins. “But then there’s a turning point beyond which we continue to consume more and more, but it actually isn’t improving our health.”

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Emily Badger
Emily Badger is a freelance writer living in the Washington, D.C. area who has contributed to The New York Times, International Herald Tribune and The Christian Science Monitor. She previously covered college sports for the Orlando Sentinel and lived and reported in France.

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