July 21, 2003 

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Climate and Disease
April 27, 2000
Dengue fever poster

It seems that each spring brings news of a dreaded new or reemerging illness. In 1998, hantavirus stalked the Southwest. Last year, Texas fought an outbreak of dengue fever, an old terror of tropical areas, and New York City battled West Nile Virus (WNV), an unwelcome immigrant that can cause deadly encephalitis.

As our planet heats up, diseases once thought extinct, along with other diseases previously unknown to humankind, gain a foothold in temperate areas. What’s in store for the United States this spring and summer? And how can we protect ourselves against these emerging diseases?

What causes the spread of these diseases?

National Science Foundation director Dr. Rita Colwell notes that climate change plays a part in the ebb and flow of infectious disease. "Global change and human health are interrelated...but this linkage [of disease outbreak] to climate has not been quantified until recently. Now we’re beginning to understand that there’s more to this relationship to climate than we thought."

The mosquito is a dangerous vector because newborns can hatch in any stagnant puddle, as above, or even a paper cup full of water, making migration easy.
Clip edited by Jed Boyar.

If you prefer to view it with RealPlayer, click here.

Even small increases in temperature can provide disease carriers (known as vectors) a friendlier climate in which to grow and reproduce. And as these vector populations increase, so does your potential exposure to the pathogens they carry.

Some vectors, such as mosquitos, carry malaria, dengue fever, and some strains of encephalitis. Deer mice spread hantavirus. And certain species of birds, after being bitten by infected mosquitos, are responsible for West Nile Virus (WNV), which in 1999 claimed the lives of seven people in New York City.

How can climate change cause disease?

One compelling example of a disease caused by global climate change is hantavirus. "The simplest explanation as to how the infectious disease and climate relationship works is the hantavirus," says Colwell, "because people can visualize in their minds very clearly a sequence of events."

As the desert warms, seeds grow more abundantly. When the food supply increases, so does the deer mice population. "The mice carry the virus, and discharge it with their urine," notes Colwell. "When the mice disperse, and when the normal season returns, the [large] mouse population begins to forage for food. So the mice end up in barns, [and] in homes." The virus is excreted in the mice’s urine, which dries into a powdery substance. When the homeowner cleans the barn or house, the dried urine is dispersed into the air. The unsuspecting person inhales the powder, and the virus enters the lungs, where it leads tohantavirus pulmonary syndrome (HPS). According to the Centers for Disease Control and Prevention (CDC), HPS kills 40 to 60 percent of infected people.

What diseases might strike this summer?

Mosquito, Aedes aegypti, is a vector of dengue fever
image: CDC

Some officials are closely watching WNV, fearing it could spead south. Other health workers worry that dengue fever could spread north. In the Southwest, the annual hantavirus alert is in high gear, and in the northern states, some are concerned that malaria could appear in Michigan and other states with many bodies of water.

But Stephen Ostroff, a West Nile expert at the CDC, cautions that people should not overreact to these microscopic menaces. "We certainly know that diseases ebb and flow, and we don’t always know why they ebb and flow. It could be that as climates change it could favor some bugs and inhibit other bugs."

How can I protect myself and my family?

The Environmental Protection Agency and the CDC list some steps you can take to keep these emerging diseases at bay:

  • Get rid of any standing water around the home, including water in potted plant containers, garbage cans, gutters or drains. Mosquitos can breed in any puddle that stands more than four days.

  • Make sure window and door screens are "bug proof."

  • Replace all outdoor lights with yellow "bug" lights.

  • Wear headnets, long sleeve shirts, and long pants when venturing into areas with high mosquito populations, like salt marshes or wooded areas.

  • Use mosquito repellants when necessary.

  • Avoid handling dead animals or birds with bare hands. Use gloves or double plastic bags to handle the carcass.

produced by Debra Utacia Krol

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