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warming may also increase the risk of some infectious diseases, particularly those diseases that only appear in warm areas. Diseases that are spread by mosquitoes and other insects could become more prevalent if warmer temperatures enabled those insects to become established farther north; such "vector-borne" diseases include malaria, dengue fever, yellow fever, and encephalitis. Some scientists believe that algal blooms could occur more frequently as temperatures warm — particularly in areas with polluted waters — in which case diseases such a cholera that tend to accompany algal blooms could become more frequent.
In spite of these risks, increased mortality is not an inevitable consequence of global warming. Malaria, for example, is rare in the United States even in warmer regions where the mosquito that transmits the disease is found, because this nation has the ability to rapidly identify and contain outbreaks when they appear. Heat-related deaths can be prevented by emergency measures to move vulnerable people to air-conditioned buildings, and by reducing the emissions of photochemical oxidants which cause ground-level ozone. Many of the impacts of climate change on health could be avoided through the maintenance of strong public health programs to monitor, quarantine, and treat the spread of infectious diseases and respond to other health emergencies as they occur. Although air-conditioning and public health programs may impose additional costs on the public and private sectors, they would often be preferable to the impacts on human health that would otherwise occur.
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