Study shows links between climate and dengue in India

Mumbai: There are intricate links between climate and dengue in India, according to a study conducted by the Pune-based Indian Institute of Tropical Meteorology (IITM).

The study says that a combination of warm temperatures above 27°C, moderate and evenly distributed rainfall, and humidity levels between 60 per cent and 78 per cent 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 led by Sophia Yacob and Roxy Mathew Koll from the IITM-Pune has been published in Scientific Reports.

The research study explores how temperature, rainfall, and humidity influence dengue in Pune, a dengue hotspot.

“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 per cent by 2030 and 23–40 per cent by 2050,” the study states.

“This collaboration highlights the importance of bringing together expertise from diverse fields to address complex climate-health challenges. It is a perfect example of how scientists, the health department, and the government can work together to improve our health warning system,” said Maharashtra Chief Secretary Sujata Saunik. 

“This study is a significant step in understanding how climate impacts health,” said Sophia Yacob, adding:  “The model we developed can be adapted to other regions, providing a valuable tool for managing climate-sensitive diseases like dengue.”

“In August 2024, my wife was severely affected by dengue and had to be hospitalised in the ICU. Hospitals in Pune were overwhelmed with dengue patients, and this experience showed me that even as a climate scientist, no one is spared during outbreaks,” added Roxy Mathew Koll.

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. It is hence important to individually assess the climate-dengue relationship for each region using available health data, it said.

The study says 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 new study has 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 dengue early warning systems can help authorities take proactive measures to prevent and manage outbreaks.