Dengue Transmission Pattern Shifts and Climate-Urbanization Nexus in South Asia

Executive Summary

South Asia faces a critical epidemiological transition where dengue transmission is extending beyond traditional seasonal windows, driven by the convergence of climate warming, erratic precipitation patterns, and rapid urbanization. According to the WHO South-East Asia Regional Office, dengue cases increased significantly in 2025, with Bangladesh reporting 102,562 cases and early 2026 travel alerts remaining active across the region. The interplay between urban heat islands and climate change is fundamentally altering mosquito breeding cycles, transforming dengue from a seasonal monsoon-associated disease into a year-round health threat that challenges existing surveillance and control frameworks.

Climate Disruption Reshaping Disease Ecology

The fundamental drivers of dengue's seasonal patterns are being disrupted by accelerating climate change across South Asia. According to research published in PLOS Neglected Tropical Diseases, temperature and rainfall variations are creating complex transmission dynamics that differ from historical patterns. Under moderate to high greenhouse gas emission scenarios (SSP585), countries show divergent trajectories: Thailand's peak transmission potential is projected to decline from 2.60 to 2.09 between the 2030s and 2090s, while Singapore faces a similar decrease from 1.63 to 1.22.

Temperature patterns favorable to mosquito activity, typically 25-35°C, are now occurring outside traditional monsoon windows. Indian hospital surveillance data shows sustained case loads extending beyond October, with transmission continuing through months that historically had minimal activity. The interplay between elevated overnight temperatures and altered precipitation creates compound effects that extend suitable conditions beyond the traditional monsoon window of May through October.

Precipitation patterns add another layer of complexity to transmission dynamics. Studies across Southeast Asian locations show that altered rainfall creates both drought-stressed urban environments with concentrated standing water and flood-prone areas with expanded breeding habitats. The resulting spillover affects public health systems that were designed around predictable seasonal patterns rather than year-round transmission pressure.

Urban Infrastructure As Disease Amplifier

The concentration of South Asia's population in rapidly expanding urban areas creates a multiplier effect for climate-driven dengue risks. Urban heat island research from India reveals that built-up areas exhibit the strongest positive correlation with dengue incidence (ρ = 0.822), far exceeding other land use types. Cities trap heat through concrete structures and poor drainage systems, creating artificial habitats that facilitate mosquito breeding through water storage systems and accumulated standing water.

Unplanned urbanization across the region compounds these risks through weak environmental management that increases potential breeding sites for Aedes mosquitoes. High population density in capital cities, combined with travel activity, further accelerates dengue epidemic potential throughout South Asian countries. Both economic and security implications emerge as urban populations face sustained disease pressure that traditional rural-focused control strategies cannot address effectively.

The broader geopolitical implications include strain on health systems that were not designed for sustained transmission pressure. Urban infrastructure deficits create cascading effects where public health capacity becomes overwhelmed during what were previously predictable seasonal peaks, now extending across longer periods with higher baseline transmission rates.

Surveillance System Transformation Requirements

Current surveillance frameworks across South Asia require fundamental redesign to address year-round transmission patterns. The WHO South-East Asia Regional Office documented significant surveillance gaps, with data often lagging two to six months behind actual transmission patterns. The March 2026 launch of the Global Dengue Observatory by the London School of Hygiene & Tropical Medicine represents an attempt to address these data gaps across 88 countries, but regional capacity remains insufficient.

Traditional early warning systems designed around monsoon seasonality are proving inadequate for current transmission dynamics. WHO operational guides for Early Warning and Response Systems (EWARS) require updating to incorporate urban heat island effects, compound climate events, and extended transmission windows that no longer align with historical seasonal patterns.

The enhancement of surveillance must integrate entomological, epidemiological, and environmental monitoring to detect increased transmission early enough for effective response. Cross-domain analysis reveals that surveillance system gaps create both immediate health risks and broader economic consequences as outbreaks become larger and more difficult to control when detection occurs late in transmission cycles.

Regional Response Coordination Gaps

The WHO South-East Asia Regional Office's September 2025 call for strengthened coordination highlighted critical gaps in regional response capacity. Nine of the ten member states report sustained dengue transmission, but response frameworks remain fragmented across national boundaries despite mosquito populations and viral circulation patterns that transcend political borders.

Climate change is exacerbating coordination challenges as traditional seasonal patterns that allowed for resource sharing between countries with different peak periods are breaking down. Countries that previously experienced complementary transmission cycles now face simultaneous high-burden periods that strain regional response capacity and limit mutual assistance arrangements.

The WHO's classification of dengue as a Grade 3 emergency in 2023 reflects the scale and complexity of current transmission patterns, but regional response architecture has not adapted to address the sustained high-risk environment created by climate-driven transmission dynamics. Both economic and political implications emerge as sustained disease burden affects trade, travel, and regional economic integration across South Asian economies.

Health Intelligence Summary

Health Metrics Dashboard

Evidence Quality Assessment

Regulatory Pipeline Table

Population Impact Matrix

WHO GOARN Response Assessment

Indicators To Watch

Decision Relevance

Scenario A (~60%): Sustained year-round transmission becomes endemic across urban South Asia — Recommended: Immediately restructure surveillance systems for continuous monitoring, redirect resources from seasonal surge capacity to sustained response capability, establish regional coordination frameworks for data sharing and joint response protocols.

Scenario B (~30%): Climate impacts prove more variable, creating mixed seasonal-extended patterns — Recommended: Develop flexible surveillance systems capable of both traditional seasonal response and extended monitoring, maintain existing monsoon preparation while building year-round capacity, pilot regional early warning systems in high-risk urban areas.

Scenario C (~10%): Temperature increases push transmission above optimal ranges in many areas — Recommended: Monitor transmission patterns for evidence of temperature-limited spread, maintain surveillance for potential shifts to cooler seasons or higher altitudes, prepare for possible reduction in traditional high-burden areas concurrent with expansion into previously low-risk regions.

Analytical Limitations

• Temperature-transmission correlation data primarily from Indian urban areas may not represent diverse microclimates across South Asian region
• WHO surveillance data lags mean current transmission patterns may differ significantly from reported figures by 2-6 months
• Climate projection models do not fully account for urban heat island effects which could accelerate or modify projected temperature impacts
• Cross-border transmission tracking remains insufficient to validate assumptions about regional coordination requirements
• Economic impact data unavailable to assess full cost-benefit analysis of surveillance system transformation versus continued seasonal response approaches