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VAN KLEEF, Esther; BAMBRICK, Hilary  and  HALES, Simon. The geographic distribution of dengue fever and the potential influence of global climate change. [online]. ahead of print, pp. 0-0.  Epub Mar 21, 2010. ISSN 2078-8606.

BACKGROUND Approximately 2.5 billion people are at risk from dengue infection. Dengue is endemic to urban populations in tropical areas; large epidemics have occurred less frequently in subtropical regions, and rarely in cities in temperate regions. The virus is transmitted by the freshwater mosquito, Aedes aegypti. During the past century, surface temperatures have increased by a global average of 0.75°C. Temperature increases of this magnitude may be associated with substantial increases in dengue epidemic potential. OBJECTIVE We aimed to describe the geographic distribution of dengue transmission (current and historical) and to estimate possible impacts on transmission from climate change. METHODS We conducted two systematic reviews. We searched PubMed, digital books and archives for literature describing geographically defined outbreaks of dengue. We also searched PubMed and Scopus for studies modelling the potential effects of climate change on dengue transmission. Data from studies meeting the inclusion criteria were considered by all of our team and we collaborated to draw our conclusions. No meta-analysis was attempted. RESULTS One hundred and one articles met the eligibility criteria for the first review; there were some contradictions and ambiguities in the data. Current global distribution of dengue is generally less extensive than historical limits of dengue-like illness. In recent years, several countries have reported local transmission of dengue for the first time, but it is unclear whether this represents true geographic spread, rather than increased awareness and reporting. Areas of geographic contraction of dengue include the southern states of North America, much of Australia, parts of southern Europe, Japan, China and South Africa. Piped water supplies, removal of water storage tanks, changes in housing conditions and vector control measures have plausibly contributed to this contraction. Six papers met the inclusion criteria for the second review. The findings of theoretical and statistical models of dengue and climate are broadly consistent: the transmission of dengue is highly sensitive to climate. Relatively small increases in temperature (around 1°C) can lead to substantial increases in transmission potential. Studies modelling the potential effects of climate change on dengue project that there will be increases in climatic suitability for transmission and an expansion of the geographic regions at risk of dengue during this century. CONCLUSIONS Geographic distribution of dengue has generally contracted, despite increases in global average temperature in the past century. Theoretically, however, temperature trends have increased the risk of dengue in some areas. The independent effect of climate change on historical patterns of dengue transmission cannot be quantified based on current evidence, as existing models of disease transmission provide limited, incomplete, projections of disease risk. The geographic limits of dengue result from a complex interaction between physical, ecological and social factors which have not been included in current climate change models. Keeping this limitation in mind, models estimating changes to geographic boundaries of transmission suggest an increase in the future population at risk of dengue. Factors associated with urban poverty and minimal capacities for surveillance and control measures remain important promoters of dengue transmission in regions with favourable climate.

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