How Climate Change is Redrawing the Global Map of Vector-Borne Disease Transmission

The impacts of climate change on human health are profound, with emerging evidence positioning climate change as one of the most significant contemporary global public health emergencies [1]. Extreme weather events, such as including heatwaves, wildfires, tropical storms, hurricanes, and floods, are increasing in frequency, severity, and geographic extent due to anthropogenic climate change [1, 2]. Beyond these acute events, one of the most pressing yet underappreciated consequences of our changing climate is its profound reshaping of global patterns of vector-borne disease (VBD) transmission [2, 3]. Vector-borne diseases such as malaria, dengue, Zika virus, chikungunya, Lyme disease, and West Nile virus have traditionally been endemic to tropical and subtropical regions [4, 5]. However, climate-driven ecological changes are altering the geographic distribution, seasonal patterns, and overall transmission intensity of these diseases worldwide [6, 7]. Increasing temperatures, fluctuating rainfall patterns, rising humidity levels, and ecosystem disruption are expanding the suitable habitats for disease-carrying vectors like mosquitoes and ticks, often beyond their historical ranges [8-10]. The rapid expansion of global travel and trade, coupled with unprecedented population growth and rampant urbanization, particularly in low- and middle-income countries (LMICs), further accelerates the emergence and re-emergence of vector-borne diseases in previously non-endemic regions [11-13]. Many vectors, particularly mosquitoes and ticks, are ectothermic organisms whose development, survival, and reproductive cycles are intricately tied to temperature and climatic conditions [14, 15]. Notably, the expansion of malaria-transmitting Anopheles mosquitoes into highland regions of East Africa, areas previously deemed unsuitable for sustained transmission highlights the tangible influence of climate change on disease risk [16]. Similarly, vectors such as Aedes aegypti and Aedes albopictus, responsible for transmitting dengue, Zika, and chikungunya, are now established in southern Europe and parts of North America [17-21]. Projections indicate that by 2080, up to 60% of the global population could be at risk of dengue, with nearly one billion people potentially facing their first exposure to mosquito-borne diseases due to climate-induced range expansion [22, 23]. In temperate regions, warmer winters and extended summers have facilitated the proliferation of Ixodes ticks, vectors for Lyme disease and tick-borne encephalitis, across areas such as Canada, Scandinavia, and the northeastern United States, driving significant rises in tick-borne infections [24]. These trends underscore that climate change is not only reshaping where vector-borne diseases occur but also influencing when, how frequently, and how intensely they emerge [1, 24]. Changes in rainfall patterns, humidity levels, and temperature regimes influence vector breeding, survival, biting rates, and pathogen development within vectors [3, 6, 25]. Climatic phenomena like the El Niño Southern Oscillation (ENSO) exemplify how climate variability triggers disease outbreaks, with documented associations between ENSO events and spikes in malaria, Rift Valley fever, and dengue in diverse regions [26, 27, 28, 29]. Furthermore, the intersection of climate change and unplanned urbanization exacerbates disease risk, particularly in LMICs where health systems remain under-resourced and ill-equipped to manage these evolving threats [30, 31].

The role of climate change on the global map of vector-borne disease proliferation is now well documented, representing a multidimensional challenge at the nexus of environmental change, public health, and socioeconomic inequity. Mosquitoes, ticks, and other arthropod vectors are highly sensitive to climatic conditions, particularly temperature, rainfall, and humidity, which directly influence their distribution, abundance, and vector capacity [14, 15]. One of the most compelling examples of climate-driven vector expansion is the encroachment of malaria-transmitting Anopheles mosquitoes into high-altitude regions of East Africa. Historically, cooler temperatures at elevations above 2000 meters acted as a natural barrier to malaria transmission. However, rising temperatures have enabled Anopheles species to establish populations in these highland areas, significantly increasing malaria risk among populations with limited acquired immunity [16].

Similarly, the global spread of Aedes aegypti and Aedes albopictus mosquitoes epitomizes how climate change, combined with urbanization and global travel, facilitates the emergence of arboviral diseases in new regions. Aedes albopictus, originally native to Southeast Asia, is now established across parts of Europe and North America, expanding the transmission potential of dengue, Zika, and chikungunya [17-21]. The implications are severe, with projections suggesting that by 2080, nearly 6 in 10 people globally could face dengue exposure, driven largely by the expansion of mosquito habitats into previously unaffected areas [22, 23]. This geographic shift is not confined to tropical regions but increasingly threatens temperate zones in Europe and North America. In North America, warmer winters and prolonged summers have facilitated the northward spread of Ixodes scapularis, the primary vector for Lyme disease, with significant increases in cases reported in Canada and the northeastern United States [24]. Tick-borne encephalitis, once confined to specific parts of Europe, has similarly expanded its range [19].

Beyond geographic range shifts, climate change also alters disease seasonality and outbreak intensity. Warmer temperatures accelerate vector development and pathogen incubation periods, leading to increased biting rates and shorter transmission cycles [3, 6, 15]. Rainfall variability creates new breeding habitats for mosquitoes, while drought conditions, paradoxically, can intensify transmission by concentrating human populations around remaining water sources [6, 25]. The ENSO phenomenon exemplifies how climatic fluctuations influence disease dynamics. El Niño events have been consistently linked to increased incidence of vector-borne diseases, including Rift Valley fever outbreaks in East Africa, surges in malaria cases across South Asia, and widespread dengue transmission in South America [26-29]. Urbanization has worsened these challenges over time, particularly in LMICs where rapid, unplanned city growth often results in informal settlements with inadequate infrastructure. Aedes mosquitoes, which thrive in artificial containers and densely populated environments, are well suited to exploit such conditions [30, 31]. Notably, cities like Dhaka, Delhi, and Nairobi have experienced unprecedented dengue outbreaks in recent years, coinciding with climate anomalies and explosive urban expansion [32, 33, 34, 35]. The burden of these climate-sensitive diseases disproportionately falls on LMICs, which face significant resource constraints in disease surveillance, healthcare delivery, and vector control [36-38]. These settings often lack robust early warning systems, adequate diagnostic capacity, and sustainable vector control programs, leaving populations highly vulnerable to climate-amplified outbreaks [36-40]. Case studies illustrate the devastating consequences of this vulnerability. In 2019, Mozambique experienced one of its worst malaria seasons following Cyclone Idai, with widespread flooding creating vast mosquito breeding grounds and overwhelming health services [41]. Similarly, Pakistan recorded over 75,000 dengue cases in the wake of catastrophic monsoon floods in 2022 [42]. Climate change also interacts with social determinants of health, particularly conflict and displacement. Environmental stressors such as drought, crop failure, and extreme weather events are increasingly recognized as drivers of forced migration and resource conflict, conditions that facilitate the spread of vector-borne diseases [2, 43]. Informal settlements, common among displaced populations, often lack adequate sanitation, housing, and healthcare, creating ideal conditions for vector proliferation and disease transmission [44]. The Eastern Mediterranean and Middle East exemplify these dynamics, where overlapping crises including armed conflict, climate change, and fragile health systems have precipitated outbreaks of yellow fever, chikungunya, and leishmaniasis [45, 46].

The WHO’s World Health Organization's Global Vector Control Response (GVCR) 2017–2030 emphasizes the urgent need for integrated, climate-adaptive vector control strategies, emphasizing community engagement, environmental management, and cross-sectoral collaboration [47]. Yet, progress remains inconsistent, hampered by funding shortfalls and fragmented implementation [47]. As shown in Table 1 below, from the highlands of East Africa to the cities of Southern Europe and North America, diseases once confined to specific geographies are now emerging in new regions, exposing millions to heightened health risks. Malaria, historically associated with low-lying tropical regions, is rapidly conquering higher altitudes, previously shielded by cooler climates. In the East African highlands encompassing Ethiopia, Kenya, Rwanda, and the Great Rift Valley, rising temperatures and increased precipitation have expanded malaria's geographic reach. These climatic shifts have made the once inhospitable highlands thermally suitable for Anopheles mosquitoes, the primary malaria vectors, leading to earlier and prolonged transmission seasons. Rwanda, for instance, is now witnessing malaria encroachment into its highland zones, a troubling testament to the disease’s climate-fueled expansion [48].

Dengue fever, transmitted by Aedes aegypti and Aedes albopictus mosquitoes, has become a glaring symbol of climate-driven disease proliferation. Increasing global temperatures and erratic rainfall patterns are extending the mosquitoes' range and lengthening transmission seasons. Southern Europe, including France and Italy has recorded local dengue outbreaks, once unthinkable in these temperate regions. Similarly, parts of the Southern United States (Florida, Texas, California) have seen rising dengue activity, coinciding with hotter summers and vector establishment. Meanwhile, Latin America is grappling with unprecedented outbreaks. In 2024, the region reported approximately 13 million suspected dengue cases, with Brazil, Argentina, Paraguay, and Colombia among the hardest-hit countries, an outbreak scale exacerbated by the confluence of warming trends and altered precipitation cycles [49, 50]. Lyme disease, transmitted by Ixodes scapularis ticks, is also experiencing a worrisome climate-linked expansion, particularly across North America and Europe. Warmer winters, a hallmark of the current climate trajectory, enhance tick survival rates and facilitate their spread into previously unaffected territories. In Canada, provinces such as Ontario, Quebec, Manitoba, Nova Scotia, and Newfoundland are witnessing significant increases in Lyme disease risk, with projections estimating a staggering 213% expansion in suitable tick habitat by the 2080s. The disease is similarly advancing across Scandinavia, including Sweden and Norway, and into the Alpine regions of Central Europe, as ticks steadily migrate northward at an estimated pace of 46 kilometers per year [51]. The 2015–2016 Zika outbreak underscored how climate variability, notably the El Niño phenomenon, compounded by long-term climate change, can create optimal conditions for disease emergence. In South and Central America, countries like Brazil, Mexico, and others experienced explosive Zika transmission, driven by favorable climatic conditions that boosted Aedes mosquito populations. Although global attention has since waned, the threat remains. The Centers for Disease Control and Prevention (CDC) continues to warn of Zika risks in Southeast Asia, including Indonesia, the Philippines, and Thailand, as well as in Mexico and parts of the United States, underscoring the persistent danger where suitable vectors and conducive climates intersect [23, 52].

As shown in Table 2 below, in recent years, a dangerous pattern has emerged across the globe whereby extreme weather events driven by climate change are igniting outbreaks of deadly vector-borne diseases, often in regions already struggling with fragile health systems. In 2015, Brazil's Northeast region was gripped by a devastating health crisis, an El Niño-fueled combination of intense rainfall and severe drought conditions set the stage for one of the most consequential outbreaks of the decade, the Zika virus epidemic. The virus, spread by Aedes mosquitoes, swept across the nation, leaving behind over 4,000 cases of microcephaly, a severe birth defect, most acutely seen in infants born in Recife, a city in Brazil. The world watched in shock as the connections between climate disruption and vector-borne epidemics were laid bare [53]. In 2016, the port city of Machala, Ecuador, became an early example of how altered weather patterns can fuel outbreaks. Unusually high rainfall and soaring temperatures created perfect breeding conditions for Aedes mosquitoes, triggering a local dengue outbreak. Scientific studies later confirmed what many suspected: the surge in dengue was tightly linked to fluctuations in rainfall and temperature cycles, marking a warning of what was to come [54]. The pattern of destruction did not stop there. In 2019, Southern Africa became the next hotspot when Cyclone Idai, one of the most powerful storms to ever strike the region, unleashed catastrophic flooding and infrastructure collapse across Mozambique and neighboring Zimbabwe. Within weeks, malaria cases in Mozambique’s Sofala province surged to nearly 15,000, with similar trends spilling over the border into Zimbabwe. Stagnant floodwaters, destroyed homes, causing displaced populations to create ideal breeding conditions for Anopheles mosquitoes, reigniting malaria transmission at unprecedented levels [41]. Fast forward to 2022, when Pakistan's Sindh province was submerged under record-breaking monsoon floods. With vast areas underwater and communities marooned, an explosion of mosquito breeding sites followed. By early September, over 3,800 confirmed dengue cases had been recorded, alongside nearly a dozen deaths. Health officials reported tens of thousands more suspected cases, compounded by a parallel surge in malaria, a stark reminder that in flood-stricken regions, multiple diseases often strike simultaneously [43]. The following year, 2023, showed how cascading climate disasters can fuel overlapping health crises. In Mozambique, Cyclone Freddy battered coastal regions, leading to severe flooding that quickly escalated into a widespread cholera outbreak. In the aftermath, health authorities reported over 21,000 cholera cases and 95 deaths, as contaminated water supplies turned deadly in communities still reeling from flood damage [55]. Meanwhile, across the Arabian Sea, Pakistan’s Karachi grappled with a post-flood malaria crisis of staggering proportions. With floodwaters lingering from the 2022 monsoons, stagnant pools became breeding grounds for mosquitoes, resulting in nearly 3 million suspected malaria cases reported during the 2022–2023 period alone, a catastrophic burden for an already strained healthcare system [56].

Despite the growing threat, most countries do not have climate-sensitive disease surveillance systems. Many rely on passive reporting, which is slow and fails to capture real-time changes in vector ecology. Integrated approaches that combine climate forecasting, entomological surveillance, and digital disease reporting are urgently needed. To address the changing map of vector-borne disease, a paradigm shift is required. Vector control must become more adaptive, context-specific, and anticipatory. The following recommendations are suggested: Predictive mapping & surveillance, which utilize climate-data integration and early warning systems to detect emerging risk zones and preempt vector invasion, should be introduced. Integrated vector control should also be considered through expanded vaccine reach, especially for malaria and dengue, habitat reduction, and targeted interventions in high-risk areas. Environmental stewardship involving reforestation, improved water management, urban planning, and biodiversity preservation would help reduce breeding sites and spillover risk. Investments are also needed in climate-resilient infrastructure, such as improved housing, drainage systems, and early warning tools that address the root drivers of vector proliferation. Health system readiness through surveillance, clinical infrastructure, diagnostics, and insecticide resistance monitoring should be adapted quickly in newly exposed regions.

The redrawing of the global map of vector-borne diseases is a warning signal. Climate change is not just altering weather patterns; it is reshaping the ecology of infectious diseases in ways that defy historical boundaries. The time to act is now. Global health security in the 21st century depends on recognizing and responding to this climate-infection nexus. Only through coordinated global action combining science, equity, and systems thinking can we adapt to a world where vector-borne diseases increasingly know no borders.