Diseases Spread as Climate Changes

Hantavirus outbreak in the Southwest U.S. suggests how global climate change can lead to rapid spread of disease. (CDC)


Deadly Virus

One day in the spring of 1993, an otherwise healthy young man was rushed to a hospital in New Mexico because he was having trouble breathing. Within hours, he died of acute respiratory failure. He had been on his way to the funeral of his fiancée who had died from similar causes days earlier. Within a week, medical experts discovered a handful of similar deaths in the Southwest. All of the victims had been young and relatively fit.

The culprit? Hantavirus. Virtually unknown in the United States before 1993, by February 2006, 416 cases of hantavirus had been found in a number of states as far-flung as Florida and New York.

Hantavirus is a lung disease that is spread by carriers like deer mice. People contract the disease by breathing in the virus that has gotten into the air through rodent droppings and urine.

Scientists suspect a link between climate change and the 1993-94 hantavirus outbreak. Six years of drought followed by heavy spring rains in 1993 produced a burst of plant growth. This in turn led to a tenfold increase in the population of deer mice. Extreme weather, such as drought and torrential downpours, will be increasingly common as the Earth heats up.
Mosquitoes and mice spread, carrying disease

Climate limits how far many diseases can spread. In the U.S., a warmer climate and the heavy, extended rains it brought likely helped spread the hantavirus. In other places, a warmer world is helping expand the ranges of insects that carry diseases like dengue and yellow fever. People who historically had little or no risk of getting these diseases could soon have to worry about them. While other measures may be effective in keeping infectious diseases at bay, climates influence will either require more stringent measures or make failures more likely.

Like hantavirus cases suddenly showing up in the U.S., outbreaks of various diseases have been reported in parts of South America and Africa that until recently had never seen them. In Mexico, dengue fever has spread above its former elevation limit of 3,300 feet and has appeared as high as 5,600 feet. In Colombia, the mosquitoes that carry dengue fever and yellow fever viruses were previously limited to 3,300 feet but have been recently found at 7,200 feet. (Epstein, P.)

While disease-carrying mosquitoes are already moving into new areas, a 1998 study provides sober results about what the future might hold. Using three different global climate change models, researchers found that a relatively small rise in temperature increases dengue’s epidemic potential. As temperatures rise, fewer mosquitoes are necessary to maintain or spread these kinds of serious, often fatal disease.

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