A new study has illustrated the links between climate and dengue in Pune, which is a hotspot for the disease.
The global burden of dengue, one of the fastest-spreading mosquito-borne diseases, is escalating under the influence of climate change, with India contributing a third of the total. Without timely interventions, rising temperatures and fluctuating monsoon rainfall could increase dengue-related deaths by 13% by 2030 and 23–40% by 2050.
The study reveals that a combination of warm temperatures above 27°C, moderate and evenly distributed rainfall, and humidity levels between 60% and 78% during the monsoon season (June–September) increases dengue incidences and deaths. Meanwhile, heavy rains above 150 mm in a week reduce the dengue prevalence by flushing out the mosquito eggs and larvae.
The study was led by Sophia Yacob and Roxy Mathew Koll from the Indian Institute of Tropical Meteorology (IITM), Pune, and was published in Scientific Reports.
In Pune, the mean temperature range of 27–35°C during the monsoon season is ideal for increased dengue transmission. Temperature influences key mosquito factors such as lifespan, egg production, frequency of egg-laying, the time between feeding and laying eggs, the virus’s development inside the mosquito, and the time it takes for symptoms to appear in humans after infection. This temperature window is specific to Pune and may vary across regions, considering its relationship with other climatic conditions like rainfall and humidity.
The study reveals that moderate rains during a week (adding up to 150 mm in a week) lead to an increase in dengue mortality, while heavy rains (above 150 mm) reduce dengue mortality in Pune through the flushing effect, where the mosquito eggs and larvae are washed out.
The study also illustrates that it is not the cumulative amount of rainfall, but rather the pattern of rainfall, that plays a crucial role in influencing dengue transmission. Thus lower number of active and break days in the monsoon, are associated with high dengue cases and deaths. Conversely, a higher number of active and break days in the monsoon, are associated with low dengue cases and deaths.
The study has also developed a dengue early warning system that incorporates all potential climate-based dengue factors (predictors) and their combined interactions with dengue at a regional scale.
Using observed temperature, rainfall, and humidity patterns, the dengue model is able to predict potential dengue outbreaks by more than two months in advance, with reasonable skill. Such early warning systems for dengue can help authorities take proactive measures to prevent and manage outbreaks.
Yacob, the lead in the study said that the model could be adapted to other regions to provide a valuable tool for managing a climate sensitive disease like dengue.
