Vector-borne illnesses, an indication of climate change?

But such ad hoc interventions alone may not help to curb the spread of vector-borne illnesses such as dengue and chikungunya 

Health authorities have expedited actions to contain the soaring dengue and chikungunya cases. According to National Dengue Control Programme Director Dr. Sudath Samaraweera, the same mosquito is responsible for both illnesses. As a preventive measure, a mosquito prevention week had been declared from 19-24 May. 

But such ad hoc interventions alone may not help to curb the spread of vector-borne illnesses such as dengue and chikungunya. This is mainly due to the fact that these mosquitos adapt to changing environments and recent studies indicate that vector-borne illnesses would experience a spike in the face of climate change. 

Global studies conducted to draw possible links between dengue transmission and climate change indicate that climate strongly influences dengue transmission because it modulates several physical and behavioural traits of mosquitoes such as adult lifespan, aquatic developmental rates, viral incubation period and biting rate, thereby altering a mosquito’s physiological potential to transmit the virus to new hosts. 

Rising temperatures can allow vectors like mosquitoes and ticks to survive and thrive in areas where they were previously unable to, expanding their geographic range. Changes in rainfall patterns can affect the availability of breeding habitats for mosquitoes, leading to increased or decreased populations in certain regions. 

On the other hand vector populations and disease distribution depend on land use, socioeconomic and cultural factors, pest control, access to health care and human responses to disease risk. In Sri Lanka a common pattern is a spike in the number of dengue cases in highly populated areas. In densely populated areas, proper sanitation and waste disposal may be inadequate, creating breeding grounds for mosquitoes.

Over 2000 cases of dengue have been reported for May alone and the National Dengue Control Unit has so far identified 38 high risk Medical Officer of Health (MOH) areas. For this year, over 20,000 cases of dengue have been reported which is a spike in the number of cases compared to 2024.  Out of these cases, over 50% of cases have originated from the Western province. According to Colombo Municipal Council’s Chief Medical Officer of Health Dr. Geethika Ratnawardena, approximately 70,000 residences identified as being at risk of dengue have been inspected, and legal action has been taken against 471 of them.

While legal action on people who are deliberately breeding dengue mosquitoes should be expedited, one of the more serious concerns is with regards to the development activities that are being approved, often damaging sensitive ecosystems such as wetlands. The Muthurajawela wetland for instance has been encroached from all corners, causing much damage. It is from the Muthurajawela wetland that streamlets and rivulets such as Ja-Ela, Dandugam Oya and Kelani River ebb and flow to the sea. But the haphazard disposal of waste and building settlements in the buffer zone of the wetland has caused much damage over the years. 

A visit to Pubudugama, one of these recently established settlements on a rainy day would speak volumes about the impacts of filling up a marshland. Already many families have abandoned their houses (which were reportedly built by a politician) due to cracks that appeared in the walls of many of them. However the fact remains that these settlements have already disrupted the natural ecosystem, paving the way for floods, which in turn would bring about a spike in vector-borne illnesses. 

While fogging and manual destruction of dengue breeding sites are usually done by volunteers of the NDCU and the CMC from time to time, more interventions are needed to eradicate the spike in dengue cases. Natural strategies to prevent the breeding of the dengue larvae such as using larvivorous fish including guppy, dandi and Nalahandaya have also proven to be effective. But according to environmentalists, freshwater fish species that feed on mosquito larvae such as Horadandiya, Tilapia and Snakeskin Gouramies have dwindled over the years. 

Therefore, while authorities deploy task forces to bring down the number of dengue cases, it is also the responsibility of authorities as well as citizens to preserve and conserve the health and diversity of important ecosystems such as Muthurajawela.  

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