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When we think of climate change, our minds often fixate on weather fluctuations and environmental degradation. Unbeknownst to many, we are grappling with the consequences of post-Weather change issues, one of which is the proliferation of dengue fever. Sri Lanka’s weather experiences significant shifts twice a year, courtesy of the equatorial monsoon. The country witnesses the southwest monsoon from May to September and the northwest monsoon from December to February. The latter, the northwest monsoon, is the key player in altering Sri Lanka’s Weather with increased rainfall. With climate change, the rainfall fall patterns are already being influenced.
So, how does environmental factor intertwine with the surge of dengue cases?
It all starts with rainwater, the initial culprit in dengue transmission, primarily driven by Aedes spp. mosquitoes. The period following heavy rains provides an ideal climate for these disease vectors to flourish. The optimal temperature range for Aedes spp. breeding lies between 24°C and 39°C, with eggs remaining viable between 22°C and 34°C. Water serves as a crucial element for their reproduction, while cold temperatures and rainfall are less pivotal for the other stages of their life cycle.
This phenomenon contributes to the high incidence of dengue in tropical nations, and in this article, we explore the connection between dengue’s prevalence and weather patterns in Sri Lanka’s Eastern Province, encompassing districts such as Trincomalee, Batticaloa, and Ampara. The Eastern Province is known as Sri Lanka’s dry zone, receiving annual rainfall between 1750mm and 2500mm. Notably, the northwest monsoon, striking in November and December, ushers in a substantial shift in dengue prevalence in this region.
Dengue cases spike significantly during December, January, February, and March, overshadowing other months. In 2021, for instance, Batticaloa district alone recorded 84% of its total 3128 patient registrations in these four months. Similarly, Trincomalee reported 66% of its annual dengue cases during this period, and 33 out of 67 cases in Ampara occurred in the same timeframe.
The trend persists year after year, with 81% of dengue patients in the Eastern Province being diagnosed during these critical months in 2021, 82% in 2020, and 58% in 2019.
It is evident here that 81 percent of dengue patients have been diagnosed in the above mentioned months in the Eastern Province. In the year 2020, 82 percent of the number of dengue patients reported throughout the Eastern Province were reported in these four months.
2017 turned out to be the year with the highest number of dengue cases Identified in Sri Lanka. How was it in the East of Sri Lanka?
The year 2017 witnessed the highest number of dengue cases in Sri Lanka’s history, with 186,101 cases reported nationwide. Interestingly, the data indicates that 56% of these cases occurred during the May-August period, primarily linked to the southwest monsoon’s rainfall. Remarkably, despite receiving significant rainfall, the Eastern Province accounted for only 25% of the year’s total cases during these months.
Although factors such as improper waste management and socio-economic issues were mentioned, the rainfall patterns was the predominant culprit during these months. The Eastern Province received less rainfall from May to August compared to the Western, Northern, and Central Provinces.
In 2017, Trincomalee, Batticaloa, and Ampara districts reported the highest number of cases during December, January, February, and March, accounting for 48% of the total. The northwest monsoon’s rainfall in 2017 was greater than that of the southwest monsoon, further exacerbating the situation.More details can be taken here
Prevalence of Dengue in Eastern Sri Lanka for the last 5 years
Over the past five years, the prevalence of dengue in Eastern Sri Lanka has been on a declining trajectory. Notably, during the COVID-19 pandemic (from March 2020 to April 2021), the predicted number of dengue cases across Sri Lanka dropped by 74%. This can be attributed to the paralysis of schools, public places, offices, and public transport, coupled with increased public awareness.
However, it’s essential to highlight that in December 2020 and January-February 2021, Batticaloa district witnessed more dengue cases than other districts in Sri Lanka. This surge is partly attributable to Batticaloa’s higher population density.
Population Density Rates Of Eastern Province
Batticaloa – 206.7km²
Ampara – 170.3 km²
Trincomalee – 161.7km²
Let’s look at the 2023 status
The intensifying Southeast monsoon rains in Sri Lanka have raised alarm within the health departments as they warn of a potential critical dengue situation. The ongoing inclement weather is exacerbating mosquito breeding, further fueling the dengue outbreak. Since the beginning of 2023, a staggering 33,742 dengue cases have been reported across the country. The highest numbers of cases are concentrated in Colombo, Gampaha, and Kalutara districts in the Western Province, as well as Batticaloa and Trincomalee in the Eastern Province, and Kandy in the Central Province, with Galle in the Southwestern Province also experiencing a significant rise in cases.
According to the latest update from the National Dengue Control Unit (NDCU) on May 18, 2023, eight districts, including Colombo, Gampaha, Trincomalee, Batticaloa, Kalutara, Kandy, Kegalle, and Galle, have reported a substantial number of dengue cases, totaling 23,222 cases. These districts have been designated as high-risk zones by the NDCU and the Regional Directorate of Health Services (RDHS) due to the rapid escalation of dengue fever. Concerningly, the number of new cases in May alone has nearly reached 6,000, heightening anxieties about the disease’s swift spread.
The current situation, marked by an active dengue outbreak and adverse weather conditions, raises the specter of a recurrence of the 2017 crisis. In that year, the same districts currently grappling with the outbreak saw a major dengue outbreak, with 68,053 cases and 205 deaths, including a significant percentage of children. Notably, approximately 42.40% of dengue cases in 2017 were reported in the Western Province.More details can be taken here
Climate change can have a significant impact on the spread of dengue fever in Sri Lanka
- Rainfall Patterns
Climate change can alter rainfall patterns, leading to increased or irregular precipitation. Dengue transmission is closely linked to water accumulation in containers, such as discarded tires, pots, and gutters, where Aedes mosquitoes, the dengue vectors, breed. Increased rainfall can create more breeding sites for these mosquitoes, thereby increasing dengue transmission.
- Temperature Increase
Rising temperatures associated with climate change can influence the lifecycle of Aedes mosquitoes. Warmer temperatures can shorten the time it takes for mosquitoes to develop from larvae to adults, leading to more generations of mosquitoes in a shorter period. This can result in a higher mosquito population and, consequently, a higher risk of dengue transmission.
- Extended Transmission Seasons
Elevated temperatures can also extend the transmission season for dengue. In Sri Lanka, where tropical conditions already prevail, an increase in temperature can lengthen the period during which mosquitoes are active and capable of transmitting the dengue virus. This prolonged transmission season can lead to more dengue cases.
- Geographical Expansion
As climate change alters temperature and rainfall patterns, it can create more favorable conditions for Aedes mosquitoes in previously unaffected regions. This can lead to the geographical expansion of dengue transmission areas, putting more people at risk.
Climate change can exacerbate the spread of dengue fever in Sri Lanka through altered rainfall patterns, increased temperatures, extended transmission seasons, geographical expansion, and impacts on human behavior and healthcare systems. Recognizing this connection is crucial for public health authorities to develop strategies to mitigate the risks and adapt to the changing climate while addressing dengue prevention and control. More details can be taken here
Also Read more – How is Climate Change Contributing to the Spread of Dengue?
Conclusion
The intricate relationship between climate change and the spread of dengue fever in Sri Lanka’s Eastern Province underscores the vulnerability of tropical regions to this mosquito-borne disease. The recurring pattern of dengue cases peaking during the months following heavy rainfall, particularly in December to March, highlights the critical role played by weather conditions in fostering mosquito breeding and disease transmission.
Over the past five years, concerted efforts have led to a decline in dengue prevalence, particularly during the COVID-19 pandemic when strict measures were implemented. However, the recent surge in cases in 2023, exacerbated by the Southeast monsoon, serves as a stark reminder of the ongoing threat.
As health authorities and communities grapple with this challenging situation, the memory of the major outbreak in 2017 looms large, underscoring the importance of proactive measures, public awareness, and targeted interventions to mitigate the impact of dengue in these high-risk zones. While Sri Lanka continues to battle this formidable health challenge, the interconnectedness of climate, weather, and disease remains a pressing concern in our changing world.
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-With inputs from Dinesh Balasri –
