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Climate Change Drives Disease To New Territory
A WHO report in 2000 found that warming had caused malaria to spread from three districts in western Kenya to 13 and led to epidemics of the disease in Rwanda and Tanzania. In Sweden, cases of tick-borne encephalitis have risen in direct correlation to warmer winters. Asian tiger mosquitoes, the type that carry dengue fever, have been reported recently as far north as the Netherlands.
As the seas warm, other breeders thrive. Cholera, a waterborne disease, emerged in South America in 1991 for the first time in the 20th century. Abetted by poverty and poor public health, it swept from Peru across the continent and into Mexico, killing more than 10,000 people.
Diseases are also expanding in a surprisingly complex dance with their environment, taking advantage of the swings from deluge to drought made more frequent by global warming, Epstein said.
A common house mosquito, called the Culex pipiens , for example, unexpectedly thrives in drought. It lives in drainpipes and sewer puddles. During long dry spells, the stagnant pools teem with protein and attract thirsty birds on which mosquitoes feed. Meanwhile, droughts reduce the populations of dragonflies, lacewings and frogs that eat the mosquitoes.
The Culex pipiens is a favored carrier of a disease first identified in a feverish woman in the West Nile district of Uganda in 1937. The disease was found again in Israel in the 1950s, and in Romania in 1996. Each outbreak followed an unusual dry, hot spell, typical of adverse weather becoming more frequent as a result of climate change, concluded researchers at the University of Haifa in Israel.
In 1999, the virus landed in New York, probably at LaGuardia Airport. Disease sleuths speculate that it was lurking in a mosquito stowaway on a plane, or in the bloodstream of someone already infected. That summer also brought unusually hot, arid weather to New York, perfect for the Culex pipiens.
Before the year was over, 62 people had been infected and seven had died, the first of them elderly. The next two years were more temperate, but when another hot, dry summer hit in 2002, the disease exploded across the United States and into Canada.
Susan Harrison, then 45, prepared a Labor Day barbecue that year with her husband and two daughters on the deck of their small house in Toronto. She was bitten by a mosquito, but shrugged it off.
In a few days, she felt a shooting pain in her legs. Within two weeks, she could not get out of bed. Her husband, Phil, rushed her to the hospital, where she was put on a respirator and spent three months in intensive care. She now maneuvers around her narrow house in a wheelchair, her legs and right arm paralyzed by West Nile virus.
Tears welled in her eyes as he spoke of her daughters, Allison, 10, and Tara, 13. "I used to do things with them, take them places," she said. Her husband, a waiter, struggles to fill the role of two parents.
West Nile virus killed 304 people in North America in 2002 and 276 the next year. The toll dropped to about 100 in 2004, probably because of cooler weather and mosquito-control measures.
West Nile has killed 22 people in Maryland, Virginia and the District since 2001.
Despite the recent drop in the death toll, birds and horses in hot western regions are still being devastated, and the disease has likely not finished with humans.
"West Nile virus hasn't gone away. People still need to be aware that it's there," said Edward B. Hayes, a medical epidemiologist with the Centers for Disease Control and Prevention in Fort Collins, Colo. "Whether we have large-scale epidemics is anyone's guess."
Climate change already is claiming more than 150,000 lives each year, with causes ranging from heat waves to respiratory illness, WHO concluded last year.
Some scientists see global warming as a natural cycle that will soon reverse itself, but for many governments, the handwriting is increasingly clear. Britain's environment minister warned last year that malaria might reach that country. South Africa's environmental affairs minister said last year that the country could face a fourfold increase in malaria by 2020. The Canadian government now attributes the boost in West Nile virus to climate change, and last year warned that the country might eventually experience dengue fever, yellow fever and malaria.
"One of the problems we have in North America is coming to grips with the fact that epidemics are still a problem," said Elliott, the lawyer. "Canadians, prior to West Nile virus, just considered mosquitoes to be annoying. We had never thought of mosquitoes as being disease carriers."