Climate Change and the Geographical Distribution of Infectious Diseases

Some infectious agents, cytomegalovirus for example, are ubiquitous in human populations, whereas most are limited in their geographical distribution. Some infectious diseases occur readily all year round; others have a strong seasonal association. A major limiting influence on these spatial and temporal variations is the climate. Temperature, rainfall, humidity, and consequent physical and ecological characteristics of the environment set limits on the occurrence of a particular infectious disease. However, many other social, cultural, behavioral, technological, biological, and environmental factors act to determine where that infectious disease actually does occur. A new and potent variable is now entering the equation: namely, climate change. Determining the extent to which climate change has altered and will alter the distribution of infectious diseases of humans is therefore a new and important challenge. Answers will often not come easily, but this vital challenge must be addressed. Human-induced climate change is now regarded, with near-unanimous shared understanding and agreement among climate scientists, as both real and manifestly happening (see http://www.metoffice.gov.uk/corporate/pressoffice/2010/pr20100728.html). Further, on current evidence and trajectories, it seems increasingly likely that global average temperature will increase by about 3°C by later this century [1]. This will inevitably affect the geography and temporality of various infectious diseases, such as airborne, waterborne, food-borne, and vector-borne diseases.