Vectors are organisms that transmit pathogens from one host to another, spreading viruses, bacteria and parasites that cause human illness. Annually, vector-borne infections are responsible for over 700,000 deaths, with arthropod vectors contributing significantly to the global burden of infectious disease. Mosquitoes are one of the most dangerous arthropods that act as disease reservoirs due to their ability to carry and spread pathogens. In particular, Anopheles, Aedes, and Culex mosquitoes principally present in tropical and subtropical regions transmit malaria, dengue, Chikungunya, Zika virus disease, yellow fever, and West Nile virus.

Mosquito-borne diseases are particularly concerning due to global morbidity and mortality caused by their high burden. According to the World Health Organization, malaria alone was responsible for 438,000 deaths in 2017 and dengue incidence has risen 30-fold in the last 30 years. The recent re-emergence of tropical diseases such as Zika virus disease in the Americas (2015) and Chikungunya in the Western Hemisphere (2013) has also caused prominent public health crises in previously unaffected regions.

The prevalence and geographic distribution of mosquito-borne disease are projected to increase in the upcoming years. A 2019 study published in PLOS Neglected Tropical Diseases by Ryan and colleagues suggests that climate change significantly impacts the intensification of these infectious diseases, presenting a significant threat to human health. Given anticipated global temperature shifts, the model predicts that the risk of Aedes-borne viral transmission will expand. As warm temperatures extend northward and southward of the equator, the ideal conditions for mosquito-borne disease transmission extend as well. These temperatures strongly influence ectothermic mosquitos, which rely on environmental sources rather than physiological sources for body heat. Vector development and pathogen reproduction, therefore, rely on the proper ecological conditions. Consequentially, naïve human populations in regions lacking previous exposure and climates suitable for these vectors — largely in Europe, the United States and Canada — are at risk for outbreaks. Although scientific consensus indicates that mosquito-borne disease expansion will occur in parallel with climate change, the relationship between disease transmission and warming temperatures is nonlinear and complex. Biological, environmental, and social factors that drive disease also influence risk, and these variables warrant consideration in projections.

Human activity alters several global processes that affect pathogen introduction. Vector distribution and vector-host interactions change consequentially. Land use patterns such as deforestation and agriculture convert natural environments into human-dominated landscapes, in turn impacting local ecology. Reduced biodiversity, altered nutrient availability, and increased access to pathogen-multiplying animal hosts are among the many effects of human practices that promote mosquito breeding and can prolong transmission seasons. Urbanization, moreover, could increase transmission risk and enable disease spread, as increasing numbers of people are living in high density areas and traveling between urban hubs.

Socioeconomic components also drive mosquito-borne disease risk, with low-income populations disproportionately affected by vector-transmitted infections. For malaria, poverty-stricken geographic regions also bear intensive disease burden (Gallup and Sachs, 2001). Although causation has not been proven between low economic growth and high malaria prevalence, disease-poverty feedbacks can reinforce the economic strain of infectious disease.

Many interacting factors influence disease distribution and prevalence, and modeling studies enhance our understanding of current and future risk. The effects of climate change on mosquito-borne tropical diseases are substantial, and it is imperative to mitigate our global warming footprint in order to reduce harmful health and environmental consequences. Surveillance and control of mosquito distribution and density offer hope in the face of vector-driven pandemics, focusing on global preparedness for and prevention of tropical disease spread.

References

Franklinos LHV, Jones KE, Redding DW, Abubakar I (2019). The effect of global change on mosquito-borne disease. Lancet Infect Dis. 19(9):e302‐e312. doi:10.1016/S1473-3099(19)30161-6

Gallup JL, Sachs JD. The economic burden of malaria. Am J Trop Med Hyg. 2001;64(1-2 Suppl):85‐96. doi:10.4269/ajtmh.2001.64.85

Hoberg, EP and Brooks, DR (2015). Evolution in action: climate change, biodiversity dynamics and emerging infectious disease. Phil. Trans. R. Soc. B37020130553. http://doi.org/10.1098/rstb.2013.0553

Lafferty KD. The ecology of climate change and infectious diseases. Ecology. 2009;90(4):888‐900. doi:10.1890/08-0079.1.

Li Y, Kamara F, Zhou G, Puthiyakunnon S, Li C, et al. (2014) Urbanization Increases Aedes albopictus Larval Habitats and Accelerates Mosquito Development and Survivorship. PLoS Negl Trop Dis 8(11): e3301. doi:10.1371/journal.pntd.0003301

Ryan SJ, Carlson CJ, Mordecai EA, Johnson LR (2019). Global expansion and redistribution of Aedes-borne virus transmission risk with climate change. PLoS Negl Trop Dis 13 (3): e0007213. https://doi.org/10.1371/journal.pntd.0007213

WHO (2014). A global brief on vector-borne diseases.

WHO (2017). Global vector control response 2017–2030.

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Noelle Yee

Noelle is a Master’s student studying host-microbiome interactions in the transplanted lung in the Department of Immunology at the University of Toronto. Interests outside of the lab include fitness, food, and travel.
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