Editing IPCC:AR6/WGII/Chapter-9 (section)

===== 9.10.2.1.2 Mosquito-borne viruses =====

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Observed impacts

Climate variability has driven a global intensification of mosquito-borne viruses (e.g., dengue, Zika and RVF), including expansion into areas with higher altitudes ( [[#Leedale--2016|Leedale et al., 2016]] ; [[#Mweya--2016|Mweya et al., 2016]] ; [[#Messina--2019|Messina et al., 2019]] ). Concerns centre on diseases vectored by the yellow fever mosquito ( ''Aedes aegypti'' ), common throughout most of sub-Saharan Africa, and the tiger mosquito ( ''Aedes albopictus'' ), currently largely confined to western central Africa ( [[#Kraemer--2019|Kraemer et al., 2019]] ; [[#Mordecai--2020|Mordecai et al., 2020]] ).

Although warming temperatures are largely responsible for increasing environmental suitability for mosquito vectors ( [[#Mordecai--2019|Mordecai et al., 2019]] ), droughts can augment transmission when open water storage provides breeding sites near human settlements, and when flooding enables mosquitoes to proliferate and spread viruses further ( [[#Mweya--2017|Mweya et al., 2017]] ; [[#Bashir--2019|Bashir and Hassan, 2019]] ). Within Africa’s rapidly growing cities, diseases vectored by urban-adapted ''Aedes'' mosquitoes pose a major threat, especially in west Africa ( [[#Zahouli--2017|Zahouli et al., 2017]] ; [[#Weetman--2018|Weetman et al., 2018]] ; [[#Messina--2019|Messina et al., 2019]] ). Dengue virus expansion may cause explosive outbreaks but the burden of dengue haemorrhagic fever and associated mortality is higher in areas where transmission is already endemic ( [[#Murray--2013|Murray et al., 2013]] ).

Projected risks

Populations of ''Aedes aegypti'' and ''Aedes albopictus'' mosquitoes and epidemics of dengue and yellow fever and other ''Aedes'' -borne viruses are expected to increase, including at high altitudes ( [[#Weetman--2018|Weetman et al., 2018]] ; [[#Messina--2019|Messina et al., 2019]] ; [[#Ryan--2019|Ryan et al., 2019]] ; [[#Gaythorpe--2020|Gaythorpe et al., 2020]] ; [[#Mordecai--2020|Mordecai et al., 2020]] ). ''Aedes albopictus'' may expand beyond western central Africa into Chad, Mali and Burkina Faso by mid-century at &gt;2°C global warming ( [[#Kraemer--2019|Kraemer et al., 2019]] ). Shifts projected in ''Aedes'' range due to changing environmental suitability, combined with rapid urbanisation and population growth, suggest that by 2050 populations exposed to these vectors in Africa may double, and by 2080 nearly triple at &gt;2°C global warming ( [[#Kraemer--2019|Kraemer et al., 2019]] ). Southern limits of dengue transmission in Namibia and Botswana, and the western Sahel, may show the greatest expansions in environmental suitability under 1.8°C–2.6°C global warming ( [[#Messina--2019|Messina et al., 2019]] ). In the warmest scenarios (RCP8.5), however, some parts of central Africa may become too hot for mosquitoes to transmit dengue, and thus at-risk populations may peak at intermediate warming levels ( [[#Ryan--2019|Ryan et al., 2019]] ). Climatic conditions favourable for mosquitoes, combined with the increase of animal trade, may result in the expansion of the geographic range of zoonotic diseases like RVF ( [[#Martin--2008|Martin et al., 2008]] ), a threat for human and animal health with strong socioeconomic impacts ( [[#Peyre--2015|Peyre et al., 2015]] ).

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