- Sri Lanka has recorded more than 56,422 dengue cases from January to July 1, adding pressure to the country’s healthcare system as the caseload continues to increase.
- DENV-2 is the dominant dengue serotype causing a higher number of infections at present, health officials say.
- According to academics, unplanned urbanization and climate change are factors contributing to the spike in dengue cases in South Asia and many other regions.
- Meanwhile, the Aedes vector is evolving and adapting, increasing the mosquito’s ability to survive in constantly changing environmental conditions, researchers say.
DEMATAGODA, Sri Lanka — Niroshan Peters, 54, a resident of Dematagoda, a densely populated suburb in Colombo, has no option but to live and work in an environment frequently polluted due to careless waste disposal. He blames authorities for not having an effective waste management system, which results in people getting exposed to unhygienic environments.
“Last week, workers from the Colombo Municipal Council (CMC) came to fumigate this area but that alone is not enough,” Peters told Mongabay. “Every time there is a surge in dengue they suddenly remember to carry out fogging and launch dengue prevention drives. But during the rest of the year people continue to dump waste in abandoned lands and contribute to a never-ending problem.” As of July 1, Sri Lanka’s National Dengue Control Unit (NDCU) has recorded a total of 56,422 dengue cases and 35 deaths. In 2025, a total of 51,000 cases were reported, indicating an alarming increase in incidence this year.
Speaking at a recent briefing, Nalinda Jayatissa, Sri Lanka’s minister of health and media, told Colombo-based journalists that the increasing number of dengue patients could overwhelm hospitals, adding “severe pressure to the healthcare system.”
A dominant serotype
In Sri Lanka, there are four dengue serotypes — a distinct variation within a species of bacteria or virus — and different serotypes emerge during different peak seasons, said Preshila Samaraweera, consultant community physician at NDCU. However, since 2017, when Sri Lanka experienced one of its major dengue outbreaks resulting in more than 186,000 suspected cases and more than 400 deaths, DENV-2 and DENV-3 were identified as the dominant serotypes, she said.
“Our studies indicate that the current infection rate due to DENV-2 is much higher,” Samaraweera told Mongabay. She said dengue cases have been reported every day, indicating a spike in disease transmission.
Reasons for this spike vary from environmental factors to people’s behaviors. According to Samaraweera, Sri Lanka has a tropical climate with warmer and humid environments, typically between 26-30° Celsius (78.8 to 86.0° Fahrenheit) and above 60% humidity levels. High humidity levels allow the dengue mosquito to extend its lifespan to several weeks. These favorable environmental conditions help the Aedes mosquito to thrive, causing rapid transmission, she added.
Samaraweera also said out of around 150 mosquito breeds found locally, only two breeds — Aedes aegypti and Aedes albopictus — are responsible for dengue.
Link to unplanned urbanization
A 2025 study on molecular epidemiology and evolutionary trends of dengue virus serotype-2 strains in Sri Lanka reported that dengue infections in Sri Lanka have intensified over the past three decades. Results of the study indicated that the Sri Lankan DENV-2 sequences circulating from 2016 to the end of 2023 belonged to a specific sub-lineage of the Dengue virus serotype 2, primarily known for causing widespread outbreaks in Asia. They were closely related to strains circulating in the same period in South Asia and Southeast Asia.
Neelika Malavige, corresponding author and a professor at the Department of Immunology and Molecular Sciences at the University of Sri Jayewardenepura told Mongabay that there has been a massive global increase in dengue infections in the past three decades. However, the worst year globally was 2024, when more than 14 million cases were reported.
“Still these numbers are highly underestimated. Compared to the rest of the world, after 2017, the dengue incidence and deaths have been relatively low in Sri Lanka. However, we are having a large outbreak currently,” Malavige told Mongabay.
She said the reasons for the marked increase could be due to several reasons. In the past 30 years, unplanned urbanization in many cities, including in Asia and Latin America, has increased Aedes breeding sites, she said.
While Colombo district recorded 11,540 dengue cases as of July 1, a significant number of cases were reported from Gampaha, Matara, Kalutara, Ratnapura, Galle, Kandy, Hambantota, Kegalle and Kurunegala districts, across six of the nine provinces.
Chamil Muthukuda, general secretary of the Public Health Inspectors’ Union in Sri Lanka, said that more cases were recorded close to towns and urban areas in each of these districts, whereas the number of cases were less in rural areas. He added that the disease spreads rapidly in places with high population density.
A vector that evolves and adapts
Sri Lanka experiences two primary peak dengue seasons following the monsoonal rains. The peak season from May to July is associated with the southwest monsoon, while the other spike is associated with the October-December northeast monsoon.
According to Malavige, another important reason for the spike is climate change. “A rise in temperatures lead to shortening of the time for the mosquito to mature and increases the biting frequency. This results in higher transmission rates. Rise in global temperatures has also caused dengue outbreaks in certain countries such as France, Spain, Italy and USA,” she added.
Muthukuda said that fogging has become an ineffective method to control the spread of dengue as they believe the vector has “adapted to the chemicals used.”
A 2021 study conducted to assess the spatial variation of insecticide resistance among Aedes populations in the Gampaha district showed that mosquito vectors have developed a resistance due to “irrational use” of insecticides “without evidence-based applications.”
“It has an impact on other insects in the surroundings but not on the targeted dengue mosquitoes. We usually conduct fogging operations in areas with a high number of suspected cases,” he said.
According to Malavige, the Aedes vector is evolving and adapting everywhere, not just in Sri Lanka.
“It is becoming more adept at surviving in changing environmental conditions. Mosquitoes are a remarkably successful species. They have been around for over 200 million years and humans around 250,000 years ago. So, they are quite able to adapt as they have done in the past,” she said, adding that an upward trend in dengue transmission is observed not just in South Asia but worldwide.
Existing interventions
Some of the interventions taken by NDCU to control the disease spread include dengue prevention drives that primarily focus on clearing potential dengue breeding sites. Most breeding sites are discarded items such as yogurt cups and coconut husks. Stagnant water pools are an ideal habitat for the dengue mosquitoes to lay their eggs.
Samaraweera said that breeding sites have been found in various premises such as schools, government and private institutions, factories and religious places. These places should be cleaned regularly to control the disease burden from increasing further, she added.
The dengue larvae are known to breed in clean water. But due to its adaptive qualities, dengue larvae have been discovered in estuarine waters as well as in the interiors of water tanks.
The most effective method to control dengue is to allow the larvae to grow and destroy them completely, Muthukuda said. According to him, the larvae trap method could be used to attract egg-laying female Aedes mosquitoes. “Thereafter, a larvicide could be used to destroy the larvae, preventing them from maturing into biting adults. But before implementing this method, dengue breeding sites in the surroundings should be destroyed completely,” he added.
In 2020, the then government introduced the Wolbachia bacteria method to control the spread of dengue across parts of Colombo as a pilot project. This method, however, is still at an experimental stage.
The way forward
Meanwhile, a 2024 study on estimating the dynamics of dengue in the Colombo district highlighted the environmental impact by quantifying the per-capita vector density. It showed that due to the influence of external factors on vector populations and disease transmission, disease control strategies may not be universally applicable. The study called for development of a comprehensive early warning system for dengue emergence in hotspots in Sri Lanka.
A contributing author on the 2021 study Kushani De Silva, an assistant professor in the department of mathematics at the U.S.-based Lamar University told Mongabay that by combining technology with scientific research, Sri Lanka could shift from being in a state of reacting to dengue outbreaks seasonally to proactively preparing to take control measures before an epidemic occurs.
“By analyzing information from past outbreaks, weather patterns, and other environmental factors, predictive models can identify trends and seasonal patterns that can help us understand when and where dengue risk is likely to increase, allowing health authorities to implement timely and targeted control measures,” she said.
Banner Image: A fumigation drive at the Fort railway station in Colombo. Image courtesy of Kithsiri De Mel.
Citations:
Ariyaratne, D., Jayadas, T. T. P., Jeewandara, C., Senadheera, B., De Silva, M., Gomes, L., Bary, F., Syenina, A., Ranasinghe, D., Kuruppu, H., Wijewickrama, A., Ooi, E. E., & Malavige, G. N. (2026 ). Molecular epidemiology and evolutionary trends of dengue virus serotype-2 strains in Sri Lanka. BMC microbiology, 26(1), 91. doi:10.1186/s12866-025-04584-2
Chathurangika, P., Perera, S.S.N. & De Silva, S.A.K. (2024) Estimating dynamics of dengue disease in Colombo district of Sri Lanka with environmental impact by quantifying the per-capita vector density. Scientific Reports, 14(1), 24629. doi:10.1038/s41598-024-76176-5
Dalpadado, R., Gunathilaka, N., Amarasinghe, D., & Udayanaga, L. (2021). A Challenge for a Unique Dengue Vector Control Programme: Assessment of the Spatial Variation of Insecticide Resistance Status amongst Aedes aegypti and Aedes albopictus Populations in Gampaha District, Sri Lanka. BioMed Research International, 2021(1), 6619175. doi:10.1155/2021/6619175
Cite this article
Kamanthi Wickramasinghe (2026). Sri Lanka intensifies fight against dengue and the mosquitos that cause the infection. Mongabay Conservation news. DOI: https://doi.org/10.66709/news-322305
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