New Delhi: With increasing climate change bringing in many more warmer days than usual and changing monsoon patterns, Pune in Maharashtra could witness an increase in deaths caused due to dengue, a mosquito-borne disease, according to a study published on Tuesday (January 21) in the journal Scientific Reports.
The study, however, also shows that analysing patterns of dengue deaths and health data across states and regions can help develop an early warning system for authorities to prepare in advance, and thus reduce deaths caused by the infection. But collaboration and sharing health data are key to this, scientists say.
Dengue and climate change
Dengue is a viral infection that spreads through the bites of infected mosquitoes. According to the World Health Organisation (WHO), an estimated 100-400 million infections occur each year worldwide, and people living in the tropics and subtropics are most at risk at contracting dengue. Common symptoms include a high fever, headache, body aches, nausea and rashes. Though the symptoms sound benign, severe dengue can be fatal – and there is no cure for the disease yet.
A multidisciplinary team of climate and public health scientists studied data on dengue mortality and meteorological conditions such as temperature and rainfall from 2004 to 2015 in Pune. They found that temperature, rainfall and relative humidity had a huge impact on dengue mortality in the city. Deaths due to dengue showed a clear seasonal trend: it was low from December to May, but rose after the onset of the summer monsoon rainfall in June, and peaked in November. The highest number of dengue deaths over the 12-year study period was 81, in the year 2014.
The team found that moderate rains spread over the summer monsoon season lead to an increase in dengue deaths. Heavy rains, however, reduce this because such rains can flush out mosquito larvae. Warm temperatures above 27°C and humidity levels between 60% and 78% elevated the risk of dengue. Based on these links between climate and dengue deaths, the team developed a model to predict the future scenarios in dengue death patterns – given that the world now witnesses climate change due to global warming caused primarily by increased carbon emissions.
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As climate change increases, temperature and humidity are also expected to increase across the country, affecting monsoon rainfall patterns and bringing in “heavy-to-extreme” rains. As per the team’s model, the increase in warmer days means that dengue in Pune is here to not just stay, but get worse.
Incorporating simulations of future climate change into their model, the team found that dengue-related mortality in the city will increase by 13% in the near future (2021–2040), by 23–40% in the mid-century (2041–2060), and 30–112% in the late century (2081–2100) – across different carbon emission pathways that can bring about corresponding increases in temperature and in turn, changes in monsoon rainfall patterns.
Importance of sharing data
However, the team found that there were lags between specific climate factors and resulting dengue outbreaks. In Pune, temperature, rainfall, and relative humidity impacted dengue mortality at a lag of five, three and two months respectively. These gaps, the study says, can serve almost like an early warning system, by providing enough time for administrations and authorities to have systems in place to prevent the spread of dengue.
“The findings of this study have significant implications for policymakers, as they provide insights into the potential impacts of climate change on dengue mortality in Pune and provide a clear pathway to extend the model to any other region,” the study noted.
“This study is a significant step in understanding how climate impacts health,” said Sophia Yacob, a researcher at Pune’s Indian Institute of Tropical Meteorology (IITM) and lead author of the study, in a press release. “The model we developed can be adapted to other regions, providing a valuable tool for managing climate-sensitive diseases like dengue.”
Dengue deaths are prevalent in states such as Kerala, Maharashtra, West Bengal, Karnataka, Tamil Nadu, Gujarat, Punjab, Haryana, Andhra Pradesh, Telangana, Rajasthan and Uttar Pradesh. However, many of these states did not share health data with the team.
“We were able to conduct this study and prepare an early warning system using health data shared by Pune’s health department,” said Roxy Mathew Koll, climate scientist at IITM, in a press release. “We approached Kerala and other states where dengue cases are high, but health departments there did not cooperate.”
“We have meteorological data readily available from the IMD. If health data is shared, we can prepare customized early warning systems for climate sensitive diseases like dengue, malaria, and chikungunya for each city or district in India. Cooperation from health departments is key to saving lives,” he added.
This collaborative study highlights the importance of bringing together expertise from diverse fields to address complex climate-health challenges, commented Sujata Saunik, chief secretary of the government of Maharashtra, who is also a co-author on the study. “It is a perfect example of how scientists, the health department, and the government can work together to improve our health warning system.”
