The ranges and impacts of a number of important pathogens may change as a result of changing temperatures, precipitation, and extreme events (Confalonieri et al., 2007; Gage et al., 2008; Paaijmans et al., 2009; Pascual et al., 2006; Patz et al., 2008), resulting in greater human exposures in many parts of the world. Increasing temperatures may expand or shift the ranges of disease vectors, including mosquitoes, ticks, and rodents. Mosquito-borne diseases that may be affected by climate change include malaria, dengue fever, the West Nile virus, and the Saint Louis encephalitis virus. The West Nile and encephalitis viruses have both been associated with drought conditions brought on by extended periods of high temperatures (CCSP, 2008a; Haines and Patz, 2004). The range of the dog tick Rhipicephalus sanguineus that carries Rocky Mountain spotted fever may also expand due to increasing temperatures (Parola et al., 2008). Other tickborne diseases that may be impacted by increasing temperatures include Lyme disease and encephalitis. Rodent-borne diseases such as the hantavirus and leptospi-rosis may also be impacted by climate change. Aside from climate change impacts on vector-borne diseases, several pathogens that cause food- and waterborne diseases are sensitive to changes in temperature, with faster replication rates at higher temperatures. In addition, waterborne disease outbreaks (e.g., cholera outbreaks in developing countries) are also associated with heavy rainfalls and flooding (Confalonieri et al., 2007).
While vector-borne diseases will all be affected by climate-related changes in temperature, humidity, rainfall, and sea level rise, the geographical range of disease vectors depends on a variety of other factors, including population movement, land use change, public health infrastructure, and emergence of drug resistance (CCSP, 2008a; Haines and Patz, 2004). In addition, while there is wide range of vulnerability to disease within and between populations, this is also dependent on multiple, interacting factors (e.g., preexisting conditions such as malnutrition). Greater understanding of the factors contributing to the spread of infectious diseases, and the role that a changing climate will play in that spread, is needed.
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