Infectious Disease - Global Warming


Infectious Disease	Extreme Weather	Conclusions

Malaria. Dengue Fever. Encephalitis. These names are not usually heard in emergency rooms and doctor’s offices in the United States. But if we don’t act to curb global warming, they will be. As temperatures rise, disease-carrying mosquitoes and rodents spread, infecting people in their wake. Doctors at the Harvard Medical School have linked recent U.S. outbreaks of dengue ("breakbone") fever, malaria, hantavirus and other diseases to climate change.

Dengue, or "breakbone", fever is a mosquito borne disease related to yellow fever. Unlike its relative, however, there is no vaccine against dengue. One strain of the disease, hemorrhagic dengue fever, is often deadly, and doctors in the U.S. and other areas into which it is expected to spread have little experience diagnosing or treating it.

The range of the mosquito which carries dengue fever is limited by temperatures. Frost kills both adults and larvae. In the past, this has prevented the disease from spreading from the tropics, but rising temperatures are changing that. It has moved steadily north in recent decades, and to higher elevations. In the United States the mosquito which carries dengue has reached as far north as Chicago.

Dengue fever has already infected victims in the US. When McAllen, Texas suffered an outbreak of the disease in 1995, the Houston Chronicle's headline read, "Warming Climate Invites Dengue Fever to Texas."

Like dengue fever, malaria is a mosquito borne illness normally limited by temperatures. Rising temperatures have expanded its range, and exposed new populations to infection. IPCC scientists project that as warmer temperatures continue to spread north and south from the tropics and to higher elevations, malaria-carrying mosquitoes will spread with them. They project that global warming could put as much as 65 percent of the world’s population at risk of infection by malaria.

Here in the United States malaria infections are already on the rise. Houston has experienced a malaria outbreak in each of the last two years. In the last three years malaria cases have occurred as far north as New Jersey, Michigan and Queens, New York. In 1997 an outbreak occurred in Florida, striking the Disney World theme park, and mosquitoes carrying the illness were discovered in New York.

Climate-related increases in sea surface temperatures and sea level can lead to higher incidence of water-borne infectious and toxin-related illnesses such as cholera and shellfish poisoning; zooplankton which can harbor cholera proliferate in warmer water temperatures, and provide a potential environmental reservoir for the disease. Cholera killed 120,000 world-wide people in 1995, most of them children.

Outbreaks of encephalitis, another illness with strong links to warmer temperatures, also appear to be on the rise. Since 1987 there have been major outbreaks in Florida, Mississippi, New Orleans, Texas, Arizona, California, and Colorado.