Mosquitoes on the move! Climate change and vector-borne diseases

Climate change has many negative effects on human health, affecting food production and leading to water scarcity, heat-related illness and air pollution.1 For travellers, temperature and precipitation changes can also enhance the spread of mosquito- and other vector-borne diseases, such as malaria, dengue, yellow fever, chikungunya, tick-borne encephalitis and Lyme disease.1,2 This column reviews how climate change impacts care and advice for travellers and the importance of regularly updating our familiarity with the epidemiology of vector-borne diseases worldwide.How climate change affects vectorsCommon vectors include mosquitoes, ticks, sandflies, midges and blackflies.2 Multiple climate-related factors impact their ability to spread disease:3Most vectors are ectothermic (cold-blooded), so they must live in environments that can regulate and sustain their internal temperature;The larval development stage often requires bodies of water or specific humidity conditions;Biting rates of vectors tend to increase with temperature to a certain threshold, after which they decline;4 andThe development and replication of pathogens within the vectors or in the environment tend to occur faster in higher temperatures.5While the optimal environmental characteristics for transmission vary across vectors, many vector-borne diseases peak at higher temperatures, to a maximum temperature limit.2,3 As global temperatures increase, the geographic regions with a sufficiently warm temperature to host these vectors and pathogens may expand into those previously not considered to be risk areas, while regions currently at risk may contract if their temperature gets too high. Modelling also suggests a potential shift among specific diseases within regions, such as a shift from malaria to dengue in sub-Saharan Africa. This is anticipated since malaria transmission via the Anopheles mosquito is optimal at 25°C, while dengue transmission via the Aedes mosquito is optimal at 29°C, making it more tolerant to increasing temperatures.2Keeping up with vector-borne disease risksTravellers and health professionals need to be aware that epidemiologic trends published historically may change over time, including geographic risk areas, seasonality and daily biting patterns. Vector-borne diseases should not be considered static risks, as advice that applied to a region previously may no longer apply today, and what applies today may no longer apply in the future.Similar risks apply here in Canada, too. For example, the tick that is capable of transmitting Lyme disease can now potentially be found almost anywhere in Ontario, while previously, risk areas were more well defined.6 Epidemics of West Nile virus were likely facilitated by climate change, and tick- and mosquito-borne diseases previously limited to the United States may also increase in risk for Canadians.7,8Care and advice for travellersPharmacists should consult regularly updated resources to determine destination-specific risks (see Box 1). TravelHealthPro is a personal favourite, with a section of the website dedicated to outbreak surveillance and regional-level maps of malaria risk coloured by level of risk and recommended precautions. Attention to recent surveillance is particularly important for tropical and temperate climate destinations, with world maps coded by Köppen Climate Classification9 available at https://www.digitalatlasproject.net/themes/climate-systems/climate-graphs.Of the vector-borne diseases, preventive options in Canada are available against malaria, chikungunya, Japanese encephalitis, and yellow fever. When making care decisions, pharmacists must consider not only the traveller’s destination country, but the specific region(s) visited within that country including elevation, rural vs. urban environment, duration of stay, season of travel, availability of and likely adherence to bite prevention measures, and the traveller’s planned activities and risk tolerance.10Advice on vector avoidance and repellents should be part of every travel consultation, keeping in mind that advice on specific mosquito species being ‘daytime biters’ versus ‘nighttime biters’ is also evolving as daily temperature patterns and, subsequently, the potential for disease transmission changes. Overlap of mosquito species within a particular region is also often significant, necessitating continuous attention to bite prevention over the course of a day.11 Travellers should be reminded that DEET (N,N-diethyl-meta-toluamide) and icaridin (also known as picaridin) are preferred for the prevention of bites when disease transmission is possible.12 Alternate agents and home remedies should be reserved for the prevention of lower-risk ‘nuisance bites’ at home, although use of Health Canada-approved repellents is advised even domestically.13SummaryClimate can directly impact the dynamics of many infectious diseases and travel-related risks. While vector-borne disease is the focus of this column, water-borne diseases such as cholera can also be impacted.14 Travellers should also be increasingly vigilant with sun protection and the prevention of heat-related illness in an evolving climate.Sherilyn Houle is an associate professor, School of Pharmacy, University of Waterloo, ON. She has her Certificate in Travel Health from the International Society of Travel Medicine (ISTM) and has been recognized with Fellow status in the ISTM for her contributions to the field of travel medicine.References:World Health Organization. Climate change. (accessed June 30, 2025).de Souza WM, Weaver SC. Effects of climate change and human activities on vector-borne diseases. Nat Rev Microbiol 2024;22(8):476-91.Caminade C, McIntyre KM, Jones AE. Impact of recent and future climate change on vector-borne diseases. Ann N Y Acad Sci 2019;1436(1):157-73.Scott TW, Amerasinghe PH, Morrison AC, et al. Longitudinal studies of Aedes aegypti (Diptera: Culicidae) in Thailand and Puerto Rico: blood feeding frequency. J Med Entomol 2000;37:89-101.Brady OJ, Johansson MA, Guerra CA, et al. Modelling adult Aedes aegypti and Aedes albopictus survival at different temperatures in laboratory and field settings. Parasit Vectors 2013;6:351.Public Health Ontario. Public Health Ontario launches new Ontario vector-borne disease tool. (accessed July 23, 2025).Ogden NH, Bouchard C, Brankston G, et al. Health of Canadians in a changing climate: advancing our knowledge for action. Ottawa, ON: Government of Canada. (accessed July 23, 2025).Allehebi ZO, Khan FM, Robbins M, et al. Lyme disease, anaplasmosis, and babesiosis, Atlantic Canada. Emerg Infect Dis 2022;28(6):1292-4.National Geographic. Köppen Climate Classification System. (accessed July 1, 2025).Connelly CR, Gimnig JE. CDC Yellow Book 2026: Mosquitoes, ticks, and other arthropods. (accessed July 1, 2025).Lippi CA, Mundis SJ, Sippy R, et al. Trends in mosquito species distribution modeling: insights for vector surveillance and disease control. Parasit Vectors 2023;16(1):302.Committee to Advise on Tropical Medicine and Travel. Statement on personal protective measures to prevent arthropod bites. Can Commun Dis Rep 2012;38(ACS-3):1-18.Houle S. The DEETails on insect repellent alternatives. Pharm Pract Business 2019;6(5):15-6.McIntyre KM, Setzkorn C, Hepworth PJ, et al. Systematic assessment of the climate sensitivity of important human and domestic animals pathogens in Europe. Sci Rep 2017;7:7134.

Mosquitoes on the move! Climate change and vector-borne diseases

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