Island, British Columbia, Canada, causing a growing epidemic of human and animal infections and deaths. It has since spread to the Pacific Northwestern United States. The fungus, which causes deadly infections of the lung and brain, had previously been found only in tropical or subtropical climates in such regions as Africa, Australia, Southeast Asia, and the South Pacific. The exact origins of this outbreak remain a mystery, but some researchers suggest that the fungus may have been introduced through the importation of contaminated trees, shoes, wooden pallets, or shipping crates.

Climate Change

Global climate change is expected to contribute to the worldwide burden of disease and premature deaths. Scientists predict that rising average temperatures in some regions will change the transmission dynamics and geographic range of cholera, malaria, dengue fever, and tick-borne diseases. Increased precipitation may raise the number and productivity of breeding sites for vectors such as mosquitoes, ticks, and snails. Rising atmospheric and surface temperatures are also increasing the intensity, frequency, and duration of heavy precipitation and flooding events, which may raise the risk of diarrheal diseases and vector-borne infections.

A number of diseases—such as malaria, dengue fever, and viral encephalitis infections—are highly sensitive to changes in the environment. The 1993 outbreak of hantavirus pulmonary syndrome (a severe acute respiratory disease) in the Southwestern United States provides a dramatic example of how acute weather events can promote disease transmission. The outbreak was traced to a steep increase in the population of deer mice that carry the virus—an increase caused by heavy rains after 6 years of drought, which led to an abundance of food sources for the deer mice. West Nile virus emerged in the Eastern United States in 1999, during the hottest and driest summer in a century. Subsequent outbreaks in the Midwest in 2003, 2005, and 2006 also coincided with heat waves. Scientists believe that hot weather may speed up both the breeding cycle of mosquitoes and replication of the virus in insects’ guts.

Several recent studies have examined the relationship between the occurrence of infectious diseases and short-term climate variation, in particular the influence of the El Niño-Southern Oscillation (ENSO) cycle on the transmission of vector-borne and nonvector-borne infections such as malaria, dengue fever, and cholera. ENSO is the irregular cycling of surface water temperatures between warm and cool phases across parts of the Pacific Ocean. Global climate change is expected to intensify ENSO-related climate variability.

Scientists are currently debating the future effects of climate change on vector-borne disease. Some

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