By Professor M. W. Amarasiri de silva

The dengue hotspot pattern observed in Sri Lanka in 2025 reflects several interconnected realities shaped by urbanisation, climate, and human mobility. Colombo continues to stand out as the country’s strongest hotspot. Its dense housing clusters, construction activity, and high daily movement of people create ideal conditions for Aedes aegypti to thrive. The combination of crowded neighbourhoods and rapid urban development ensures that even small pockets of stagnant water become breeding sites, allowing the mosquito population to regenerate quickly, despite control efforts.

Gampaha and Kalutara together formed a continuous coastalurban dengue belt. These districts share similar environmental and demographic characteristics—large suburban populations, expanding commercial zones, and frequent waterlogging during monsoons. Their proximity to Colombo also contributes to the spread of dengue, as human movement between districts facilitates the circulation of the virus. This coastal belt has become one of the most persistent dengue-affected regions in the country.

Kandy has shown elevated transmission, driven by hillside urbanisation and household waterstorage practices. As the city expands into hilly terrain, construction sites, terraced housing, and irregular drainage systems create numerous microhabitats for mosquito breeding. In many areas, residents rely on stored water due to intermittent supply, and these containers often become breeding grounds, if not properly covered. The combination of climate, geography, and human behaviour makes Kandy a recurring hotspot.

Kurunegala has emerged as a major inland hotspot with repeated outbreaks. Its role as a transportation hub, coupled with rapid suburban growth, has led to increased mosquito density. The district’s mix of urban and semiurban environments provides abundant breeding sites, and seasonal rainfall patterns further amplify transmission cycles. Kurunegala’s dengue burden has remained consistently high over the past decade.

Batticaloa and Trincomalee experienced rising case numbers, linked to rapid development and monsoon-driven breeding cycles. Both districts have seen significant expansion in housing, tourism, and infrastructure. Heavy monsoon rains frequently create standing water in lowlying coastal areas, while new construction sites add additional breeding opportunities. These conditions have contributed to a noticeable increase in dengue transmission in the eastern region.

Jaffna, meanwhile, faces periodic spikes, influenced by climate variability and urban expansion. The district’s unique climatic conditions, particularly rising temperatures and irregular rainfall, have made mosquito breeding more favourable in recent years. Urban growth, combined with waterstorage practices common in the peninsula, has created environments where dengue outbreaks can flare unexpectedly. These periodic spikes highlight how climate change and development patterns are reshaping dengue risk in northern Sri Lanka.

One Sri Lanka’s most persistent public health emergencies

Dengue fever has entrenched itself as one of Sri Lanka’s most persistent public-health emergencies, with the country recording more than 80,000 cases in 2023 and surpassing 60,000 cases by mid-2024, according to national surveillance data. In some years, the toll has climbed even higher, with 2017 marking a historic peak of over 186,000 cases, overwhelming hospitals and prompting emergency responses across multiple districts. Colombo, Gampaha, Kandy, Kurunegala, and Batticaloa have repeatedly emerged as hotspots, reflecting a pattern in which densely populated urban and semi-urban regions bear the brunt of transmission. The economic cost is equally staggering: dengue-related healthcare expenditure, lost productivity, and household financial strain collectively amount to billions of rupees annually. These figures underscore a reality that Sri Lanka has lived with for decades; dengue is not merely a seasonal illness, but a structural challenge woven into the country’s environment, infrastructure, and public-health landscape.

Resilience of Aedes aegypti mosquito

Despite extensive public-health campaigns, fogging operations, school-based awareness programmes, and community clean-up drives, dengue continues to return with alarming regularity. The Aedes aegypti mosquito, the primary vector of dengue, has adapted with remarkable efficiency to Sri Lanka’s climate and human behaviour. It thrives in warm, humid conditions, breeds in even the smallest containers of stagnant water, and has evolved to exploit the very environments humans create, construction sites, household water storage, discarded plastic, and clogged drains. Its eggs can survive for months in dry conditions, waiting for the slightest moisture to hatch. This biological resilience has made dengue control a formidable challenge, one that traditional methods alone have struggled to overcome.

Fogging, a widely used method in Sri Lanka, targets adult mosquitoes but has limited reach. It cannot penetrate every corner of a neighbourhood, nor can it eliminate eggs or larvae hidden in sheltered containers. Larviciding is more targeted but requires consistent application and community cooperation, both of which are difficult to sustain over long periods. Public-awareness campaigns, though essential, often face behavioural fatigue. People may clean their surroundings diligently for a few weeks, only for old habits to return once the immediate threat seems to have passed. The mosquito’s ability to exploit even small lapses in environmental cleanliness allows it to rebound quickly. As a result, Sri Lanka finds itself trapped in a cycle of control, decline, and resurgence that has persisted for years.

New possibilities

In recent years, however, scientific developments emerging internationally have introduced new possibilities for dengue control, particularly biological methods that intervene directly in the mosquito’s reproductive process. One such approach involves releasing specially bred male mosquitoes that carry a biological trait preventing their offspring from surviving. These males, which do not bite and, therefore, pose no risk to humans, are released into areas with high mosquito density. They mate with wild females, and the resulting larvae inherit the trait that causes them to die before reaching adulthood. Over time, this leads to a significant reduction in the mosquito population. Field trials in several countries have shown reductions of more than 80 percent in targeted areas, a level of suppression far greater than what traditional methods typically achieve.

Precision is the key

What makes this approach particularly compelling is its precision. It targets only the dengue-carrying mosquito species without affecting other insects or the broader ecosystem. Unlike chemical insecticides, which can harm beneficial species and contribute to environmental contamination, this biological method is species-specific and environmentally safe. It also leverages the mosquito’s own behaviour specifically, the male’s strong ability to locate females, to deliver the intervention effectively. The method does not rely on perfect community compliance or constant human vigilance. Even if some breeding sites remain, the released males continue to seek out females and disrupt the reproductive cycle. This makes the approach resilient in real-world conditions where complete environmental cleanliness is difficult to achieve.

Sri Lanka’s dengue situation aligns closely with the conditions under which this biological method has proven effective elsewhere. The country’s warm climate, high humidity, and dense urbanisation create ideal breeding conditions for Aedes aegypti. Urban areas, such as Colombo, Gampaha, and Kandy, experience repeated outbreaks, often linked to rapid development, inadequate waste management, and the proliferation of small water-holding containers. Semi-urban and rural areas are not spared either, especially where household water storage practices create opportunities for mosquito breeding. The mosquito’s adaptability means that even well-intentioned community efforts can fall short. A single forgotten bucket, a clogged drain, or a neglected construction site can become a breeding hotspot capable of sustaining transmission.

Strong foundation for biological methods

Sri Lanka’s public-health infrastructure, however, offers a strong foundation for integrating new biological methods into existing dengue-control strategies. The Epidemiology Unit, local Medical Officer of Health (MOH) offices, and Public Health Inspectors (PHIs) maintain detailed surveillance systems that track dengue cases and mosquito density. These systems allow authorities to identify high-risk zones and respond quickly during outbreaks.

The country has experience with biological control in agriculture and environmental management, meaning the concept of using biological methods to suppress pests is not unfamiliar. Sri Lankan scientists and institutions, including the Medical Research Institute and several universities, have the capacity to collaborate with international partners to evaluate and implement such approaches.

If Sri Lanka were to explore the biological suppression method, pilot projects could be conducted in selected high-density urban areas. These projects would involve releasing specially bred male mosquitoes over several months and monitoring changes in mosquito population density and dengue case numbers. The results would provide valuable data on the method’s effectiveness under Sri Lankan conditions. If successful, the approach could be expanded gradually to other districts. Importantly, this method would not replace traditional control measures but rather complement them. Community clean-up efforts, larviciding, and personal protection would remain essential components of dengue control. The biological method would strengthen the overall strategy by attacking the mosquito population at its root, reducing the number of mosquitoes capable of transmitting the virus.

The potential benefits for Sri Lanka are significant. A sustained reduction in mosquito populations would lead to fewer dengue cases, less pressure on hospitals, and reduced economic burden on families and the healthcare system.

Schools would face fewer disruptions, and communities would experience greater peace of mind during monsoon seasons. The environmental advantages are also noteworthy. Reducing reliance on chemical insecticides would help protect beneficial insects and reduce chemical exposure for humans. The biological method’s species-specific nature ensures that it does not interfere with ecological balance.

Sri Lanka’s dengue challenge is not merely a medical issue but a social and economic one. Families often face financial strain when a member falls ill, especially if hospitalisation is required. Parents worry about children during school outbreaks, and workplaces experience reduced productivity when employees are affected. The psychological burden is also considerable. Dengue outbreaks create anxiety, particularly when severe cases or fatalities occur in the community. A more effective and sustainable control method would alleviate these burdens and contribute to national well-being.

The country’s experience with COVID-19 demonstrated the importance of scientific innovation, public-health preparedness, and community cooperation. Sri Lanka mobilised resources, strengthened surveillance, and adopted new technologies to manage the pandemic. The same spirit of innovation and collaboration can be applied to dengue control. Biological suppression methods represent a new frontier in public health, offering tools that are more precise, sustainable, and effective than traditional approaches. By exploring these methods, Sri Lanka can position itself at the forefront of dengue-control innovation in South Asia.

Of course, any new method must be evaluated carefully. Public acceptance is crucial, and communities must be informed about the safety and purpose of releasing male mosquitoes. Transparent communication, community engagement, and scientific oversight would be essential components of any pilot project. Sri Lanka has a strong tradition of public-health education, and this can be leveraged to ensure that communities understand and support new approaches. The involvement of local scientists and institutions would also help build trust and ensure that the method is adapted appropriately to Sri Lankan conditions.

The fight against dengue requires both persistence and innovation. Traditional methods have served the country well but have not been able to eliminate the threat. The mosquito has proven too adaptable, too resilient, and too deeply embedded in the environment. To break the cycle of recurring outbreaks, Sri Lanka must consider new tools that go beyond conventional approaches. Biological suppression methods offer a promising path forward, one that aligns with scientific advances, environmental sustainability, and the practical realities of mosquito behaviour.

Sri Lanka stands at a crossroads in its dengue-control journey. The country can continue relying solely on traditional methods, accepting the recurring burden of outbreaks, or it can embrace new scientific approaches that offer the possibility of long-term suppression. The choice is not between old and new but between a limited toolkit and a more comprehensive strategy. By integrating biological methods into its dengue-control efforts, Sri Lanka can strengthen its ability to protect communities, reduce disease burden, and build a healthier future.

The challenge is significant, but so is the opportunity. Dengue has shaped Sri Lanka’s public-health landscape for decades, but it does not have to define the country’s future. With scientific innovation, community cooperation, and strategic planning, Sri Lanka can move toward a future where dengue is no longer a seasonal crisis but a manageable threat. The biological suppression method represents one of the most promising tools available today, and its relevance to Sri Lanka is clear. The time has come to explore it seriously, evaluate it rigorously, and consider how it can be integrated into the nation’s ongoing fight against dengue.

In moving toward this future, Sri Lanka would benefit from adopting a clear policy direction that recognises dengue as a long-term structural challenge requiring modern solutions. A national policy framework could begin with pilot deployments of biological suppression methods in selected high-risk districts, supported by rigorous scientific monitoring and community engagement. It could establish partnerships between local research institutions and international experts to ensure that the technology is adapted safely and effectively to Sri Lankan conditions. The policy could also strengthen environmental management systems, ensuring that waste disposal, urban planning, and water-storage practices reduce opportunities for mosquito breeding. Public-health education could be expanded to emphasise both traditional preventive measures and the role of new biological tools. Over time, the policy could evolve into a nationwide programme that integrates biological suppression with surveillance, environmental management, and community participation, creating a comprehensive and sustainable dengue-control strategy.

Such a policy would not only reduce dengue transmission but also demonstrate Sri Lanka’s commitment to scientific innovation and public-health leadership. It would signal a shift from reactive crisis management to proactive disease suppression, offering hope to communities that have endured the burden of dengue for far too long. The path forward requires courage, collaboration, and a willingness to embrace new ideas. But the reward, a healthier, safer, and more resilient Sri Lanka, is well worth the effort.

Integrating new developments into dengue control strategies offers a promising opportunity for Sri Lanka to enhance public health and protect communities across the island. By adopting innovative solutions, improving mosquito management, and building stronger public awareness, the country can significantly reduce infection rates and relieve pressure on healthcare facilities. I hope the government will pay attention to this new development in dengue control and take positive measures to address the issue, ensuring a safer and healthier future for everyone.

The following are some scientific papers explaining the new method for Sri Lankan scientists to follow. Research on Wolbachia-mediated biological control demonstrates that introgressing Wolbachia bacteria into Aedes aegypti populations significantly limits virus transmission and alters reproductive mechanisms (Al Noman et al., 2023).

Systematic reviews evaluating mathematical models of vector control highlight that biological methods, including the release of Wolbachia-infected mosquitoes, copepods, and larvivorous fish, offer self-sustaining mechanisms for reducing dengue transmission compared to traditional chemical alternatives (Ogunlade et al., 2023).

Broader vector-control frameworks integrate biological control alongside disease surveillance and biotechnological innovations as essential components of a multi-pronged approach to dengue mitigation (Procopio et al., 2024).

Also, there are number of TED talks on the subject such as TED talk on biological control of dengue fever. You may google and find these valuable discussions which explains the method