Climate change: A driver of increasing vector-borne disease transmission in non-endemic areas
Authors: Shlomit Paz
Journal: PLoS Medicine (2024)

Climate change can affect human health in complex ways, both directly (e.g., exposure to extreme temperatures) and indirectly (e.g., changes in infectious disease ecology), compounded by a multiplicity of biological, ecological, and socioeconomic factors.The transmission of vector-borne diseases (VBDs) is highly complex and multifactorial, and is impacted by a multiplicity of biological, ecological, socioeconomic, demographic, and human-caused factors, including climate, migration, global trade, and travel among many others.Although climate is one of several drivers, it is recognised as a major environmental factor influencing the distribution of VBDs.Climate change exacerbates the risk and burden of both vectors and pathogens and allows their introduction and dispersion into new regions [1].Disease vectors (predominantly mosquitoes and ticks) capable of transmitting VBDs rely on external sources of heat to maintain their temperature within functional limits.As such, climatic conditions are major determinants in the physiology, ecology, development, and behaviour of vectors and also influence biological processes in the life cycles of pathogens [1,2].When temperatures rise, these biological processes may be accelerated.For example, during heat waves, high temperatures increase the biting rate of female mosquitoes.Since disease transmission to humans occurs during blood feeding, higher biting rates lead to higher disease incidence [2].Although the interaction between climatic variables and VBD transmission is complex, often nonlinear, and variable among different vector/pathogen combinations, there is clear evidence supporting an association between climate change and VBD transmission [3].Malaria and dengue remain of significant concern, with 249 million malaria cases in 2022 [4] and 740.4 dengue cases per 100,000 population globally in 2019 [5].However, substantial declines have occurred in recent years which can be attributed to economic development and the success of public health interventions.Between 2000 and 2019, malaria case incidence declined globally from 81 to 57 per 1,000 population at risk and malaria deaths decreased by one-third.Increased use of dual-ingredient insecticide-treated bed nets, improved diagnostic testing, and expanded access to artemisinin-based combination therapies contributed to this decline [4].These achievements demonstrate the ability to reduce infectious disease transmission and highlight the difficulty in conclusively attributing and quantifying the impact of climate change as one of many complex factors influencing VBD transmission.Climate change is a contributory factor in the expansion of geographical distribution of VBDs, since warmer conditions facilitate the establishment of vectors in new regions.Currently, tropical species are spreading towards the poles, and species are established at higher elevations due to the rising temperatures.As a result, we now observe the spreading of disease vectors to new, including non-endemic, areas due to improved (warmer) habitat suitability [6].Pathogens may be dispersed into non-endemic regions through travel, trade or migration,