Three-year-old Nethmi Sehansa* from Dematagoda, a suburb of Colombo, succumbed to dengue in May 2023. Her parents and elder siblings remain devastated by her untimely demise. Even though they had big plans for their little daughter, the dengue endemic shattered their dreams.
The Western Province of Sri Lanka had been identified as a high-risk Medical Officer of Health (MOH) area since 2010 with a high density of dengue infected patients. As of March 1, 2025, as many as 4119 cases have been reported from the Western Province, which is the highest recorded number of patients among nine other provinces in the country. The fact that many dengue cases have been reported during a usually low peak season has raised concerns among health officials.
As of March 1, 2025, as many as 4119 cases had been reported from the Western Province
Western Province of Sri Lanka had been identified as a high-risk Medical Officer of Health (MOH) area since 2010
Increasing evidence also suggests that peak dengue seasons may stretch due to unseasonal rains and warmer temperatures
Surge in dengue cases
Dengue is a viral infection transmitted following the bite of infected Aedes species of mosquitoes. According to the National Dengue Control Unit, dengue has a seasonal transmission with two peaks occurring with monsoon rains between June-July and October-December respectively.
Usual symptoms of dengue fever include high fever, pain behind eyes, severe headache, nausea, vomiting etc. Little Sehansa had had high fever and her parents took her to the hospital on the second day. The doctor had asserted that her platelet count was low and advised her parents to admit her to the hospital. Unfortunately, the doctors couldn’t save her life.
Since the beginning of 2023, the National Dengue Control Unit (NDCU) in Sri Lanka has reported 36,628 dengue cases. These figures are around three times higher than the cases reported during the same period in 2021 and 2022.
A 2024 research conducted to investigate reasons behind the outbreak of dengue in 2023 explains the fluctuating incidence of dengue fever that occurred in Sri Lanka since 1989. The largest outbreak due to dengue was reported in 2017 with 186,101 cases, associated with the cosmopolitan strain of the dengue virus (DENV) serotype 2. DENV-2 continued to be the predominant circulating serotype until October 2019. In Sri Lanka, the number of cases began to gradually increase from June 2022 onwards with a total number of 89,799 cases reported in 2023, with 18,650 from Colombo equivalent to one fifth of the caseload. Usually, Sri Lanka has two seasons of intensified dengue activity coinciding with the monsoon seasons. One season typically spans November to early February and the second season runs from May to July.
According to Dr. Preshila Samaraweera, Consultant Community Physician at the NDCU, the endemicity of the dengue virus has increased since 2000. “Therefore the number of cases cannot be brought down to zero even during a drought period. Due to the tropical climate the incidence of dengue is high and there is high transmissibility,” said Dr. Samaraweera.
When asked why there had been a sudden spike of dengue cases during the pre-monsoon period in 2025, Dr. Samaraweera said it cannot be described as a surge in cases because a similar trend had been observed during the past few years during the same period.
Dengue vector and climate change
But increasing evidence also suggests that peak dengue seasons may stretch due to unseasonal rains and warmer temperatures.
More rain also creates more stagnant water bodies and receptacles that mosquitoes may breed in. Three of the four stages of the mosquito life cycle take place in water – eggs are laid in pools of stagnant water, which hatch into larvae and pupae which develop within them.
A 2020 research on climate change induced vulnerability and adaptation for dengue incidence in Colombo and Kandy explores how numerous models have predicted that climate change would increase the geographic distribution and potential risk of dengue incidence.
Relative humidity is a vital factor, which directly enhances the feeding frequency, inter sexual attractions and oviposition rates of Aedes mosquitoes. The adult longevity and survival success after being infected by DENV have also been found to increase under high humid conditions leading to a wide geographical dispersion of dengue.
Colombo – A high risk MOH area
As for the Colombo district, a combination of factors make it a highly vulnerable area for dengue fever. A study on the impact of environmental factors on the spread of dengue fever in Sri Lanka reveals that dengue fever incidence was caused by following factors: precipitation, wind, urbanization, land management, socio-demographic characteristics.
Consequently, western province possessed higher dengue cases (41% in 2017) than the eastern parts of the country (7% during the 2017 outbreak).
A 2024 research on dengue dynamics and environmental impact indicates that in Sri Lanka, the tropical climate, marked by seasonal weather primarily influenced by monsoons, fosters optimal conditions for the virus to spread efficiently. This heightened transmission results in increased per-capita vector density. Dr. Samaraweera further said that every year 45-50% of cases are always being reported from the Western Province of Sri Lanka. “Out of 57 MOH areas in the Western Province, a high number of cases are often being reported in areas such as Nugegoda. The reasons are manifold including high population density, flash flood situations after a heavy rain that would usually increase the number of stagnant water bodies and most importantly the lack of a proper solid waste management system,” said Dr. Samaraweera.
She said that potential breeding sites for the dengue vector include discarded items such as yoghurt cups, coconut shells etc., mostly found in the backyards of houses and commercial buildings.
Speaking about changes in weather patterns over the years, Dr. Lareef Zubair, Principal Scientist at the Federation of Environment, Climate and Technology, observe some ‘unusual rain events’ in dry seasons thereby delaying wet seasons at times. It appears that the frequency of such extremes has changed.
 The endemicity of the dengue virus has increased since 2000. Therefore the number of cases cannot be brought down to zero even during a drought period. Due to the tropical climate the incidence of dengue is high and there is high transmissibility– Dr. Preshila Samaraweera, Consultant Community Physician at the NDCU |
“Certainly, the temperature highs, the air quality highs and evaporation has been exacerbated due to the already observed climate change. The argument that the warmer atmosphere has the capacity to hold much greater amounts of water vapour is sound and when large clouds burst it can lead to extreme rainfall,” said Dr. Zubair who had been observing weather patterns over the past 15 years.
He further said that people are experiencing a hydrological change. “Both maximum and minimum temperature is higher than in the last century. As a result, evaporation is much higher. Sri Lanka experiences lower air quality, which influences rain formation and the acidification of rain,” he stated.
Dengue infection and non-economic losses
So far, the dengue infection has claimed four lives during the first two months of 2025. In 2024, dengue claimed the lives of 24 individuals. Dr. Samaraweera further said that by reducing the number of cases, it would also save the expenses borne in treating patients with dengue. “When a patient is diagnosed with dengue, his or her economic productivity drops for three weeks. On the other hand the intensity of the infection varies from person to person. Therefore as the apex body to control dengue infections, we carry out targeted interventions such as fogging activities, source reductions and so on,” she added.
A 2014 study done on the economic cost of non-fatal paediatric dengue cases indicate that the average cost to hospital per case of dengue haemorrhagic fever (DHF) and dengue fever (DF) was SLR 24,856 (US$ 191) and SLR 10,348 (US$ 80) respectively.
Sehansa’s case is a classic example which indicates that dengue infection affects individuals irrespective of age. Other non-economic losses associated with dengue fever includes potential long-term health complications and psychological impact on caregivers.
However, the NDCU has been taking various measures to bring down the frequency of deaths by dengue. Dr. Samaraweera said that compared to 72 deaths in 2023 the number of deaths were brought down to 24 by 2024,” she added.
According to WHO, improper water storage practices and high population density are risk factors for dengue. But even though the authorities are taking steps to bring down the cases of dengue, V. Chithra, Sehansa’s mother, claims that even though fogging activities are being conducted by authorities on a regular basis, none of those interventions could save her daughter. “Fogging alone isn’t enough. If you check around these flats, the drainage systems are blocked and there are many stagnant water bodies. People aren’t interested in cleaning their sewage lines or cleaning the surroundings because poverty is a bigger burden they have to face on a daily basis,” she added.
In her comments, Dr. Anoja Dheerasinghe, Consultant Community Physician at NDCU said that there’s no stigma attached to the dengue infection unlike for diseases such as tuberculosis and HIV. When asked whether the urban poor is more vulnerable to the dengue infection Dr. Dheerasinghe said that people in highly populated areas are more vulnerable. “The population density in underserved settlements is high and the mosquitos’ flight range is between 100-200 metres. Therefore chances of an outbreak is highly likely in these areas and people therefore have to take all precautions,” she underscored.
 The temperature highs, the air quality highs and evaporation has been exacerbated due to the already observed climate change. The argument that the warmer atmosphere has the capacity to hold much greater amounts of water vapour is sound and when large clouds burst it can lead to extreme rainfall– Dr. Lareef Zubair, Principal Scientist at the Federation of Environment, Climate and Technology |
According to the newly drafted National Strategic Plan for Prevention and Control of Dengue – 2024-2030, Sri Lanka has made a commitment to reduce dengue deaths to zero by 2030. The authorities are determined to bring down the average infection rate by 40%. But whether increasing risk factors such as climate change and the adaptability of the dengue vector would pose significant challenges in reaching this target, remains a doubt.
*Child’s name withheld on request from parents under conditions of anonymity
This story was produced under the CIR- CANSA Media Fellowship Programme. The It was originally published in Daily Mirror on 06 March 2025.
