Dengue outbreaks in Bangladesh are lasting longer, spreading beyond Dhaka, and becoming increasingly unpredictable as climate variability, rapid urbanization, and other factors reshape the country's disease landscape.
A growing body of research suggests that rising temperatures, irregular rainfall, and humidity are influencing the spread of Aedes mosquitoes, which transmit the dengue virus. However, scientists say climate change alone cannot explain Bangladesh's evolving dengue pattern. Instead, they point to a combination of climate variability, El Niño, rapid urbanization, mosquito-control limitations, human behavior, and changes in circulating dengue virus types.
Bangladesh experienced its worst dengue outbreak in 2023, recording more than 321,000 hospitalized cases and over 1,700 deaths, according to official data.
The unprecedented outbreak prompted researchers to examine why dengue was spreading beyond its traditional hotspots, becoming less predictable, and emerging at different times of the year.
Research has consistently found strong links between local weather conditions—particularly temperature, rainfall, and humidity—and dengue transmission. Warmer temperatures accelerate mosquito development, increase biting activity, and shorten the time needed for the dengue virus to become infectious inside mosquitoes.
A study published in Scientific Reports found that local temperature and rainfall were more closely linked to dengue transmission than large-scale climate events such as the El Niño–Southern Oscillation (ENSO), suggesting El Niño influences outbreaks primarily by altering local weather conditions.
More recent spatial and time-series studies have also shown that dengue risk varies across districts because climate interacts with local factors such as population density, water-storage practices, drainage conditions, and mosquito-control capacity.
Public health expert Dr Mushtaq Hossain said El Niño-related environmental changes can create favorable conditions for dengue transmission.
“Due to the impact of El Niño, temperatures increase, rainfall patterns change, and humidity in the air rises. These environmental changes create favorable conditions for Aedes mosquito breeding, increasing the risk of dengue transmission,” he told Dhaka Tribune.
He said rainfall patterns play a crucial role because mosquito breeding depends not only on the amount of rainfall but also on its timing and distribution.
“Intermittent rainfall allows water to collect in different places, where Aedes mosquitoes can lay eggs and reproduce. However, during excessive rainfall, accumulated water may sometimes be washed away,” he said.
Dr Mushtaq added that warmer weather also affects mosquito biology.
“Extreme heat increases mosquitoes' metabolism. At the same time, warmer temperatures allow the dengue virus inside mosquitoes to become infectious more quickly,” he said.
Although climate conditions are becoming increasingly important, experts caution against treating climate change as the sole driver of dengue outbreaks.
Dr Kabirul Bashar, professor in the Department of Zoology at Jahangirnagar University, said dengue outbreaks result from several factors working together.
“It is not that dengue has increased entirely because of climate change. There are many factors, including unplanned urbanization, mosquito-control failure, and behavioral patterns. Multiple factors play a role together in dengue transmission,” he told Dhaka Tribune.
He said El Niño can influence dengue risk through changes in temperature but cannot, by itself, explain why outbreaks occur.
“El Niño has an impact, but it does not mean dengue is happening only because of El Niño. Different factors influence transmission in different ways in different areas,” he said.
Dr Bashar said local environmental and behavioral factors often determine the intensity of outbreaks.
“For example, in some areas of Barisal, people store water because of iron-related problems in the water supply. Stored water can serve as breeding grounds for Aedes mosquitoes and contribute to dengue transmission,” he added.
In 2023, Dr Bashar presented research on the potential impact of climate change on dengue transmission through Aedes mosquitoes in Bangladesh, highlighting how rising temperatures and environmental changes could influence future transmission patterns.
Experts say dengue's changing behavior is driven not only by mosquitoes but also by the virus itself.
Public health expert Tajul A Bari said seasonal conditions, temperature, and dengue virus characteristics together influence outbreaks.
“El Niño has an impact. Temperature is related to mosquito breeding, and when the environment becomes warmer, the mosquito population can increase,” he told Dhaka Tribune.
He said climate change and global warming may have helped dengue spread across wider parts of Bangladesh by making more areas environmentally suitable for mosquitoes.
However, he said preventing dengue remains challenging because of the circulation of multiple virus types.
“There are four strains of dengue virus. In Bangladesh, dengue serotypes 2 and 3 are more common. The idea that infection with one strain means a person will not get dengue again is not correct,” he said.
He added that vaccination remains another challenge. Although three dengue vaccines are available globally, access remains limited.
“One dengue vaccine has not even reached Bangladesh,” he added.
Researchers say Bangladesh's evolving dengue pattern requires a shift from short-term seasonal responses to year-round preparedness, as the factors driving transmission continue to change.
Experts recommend integrating climate forecasts, mosquito surveillance, and hospital admission data to identify high-risk periods and areas before outbreaks accelerate.
They say temperature, rainfall, and humidity trends can provide early warning signals. However, controlling dengue will ultimately depend on stronger urban management, more effective mosquito control, and greater community participation.
Researchers say Bangladesh can no longer treat dengue as a seasonal emergency confined to the monsoon months. As climate variability, urban growth, mosquito ecology, and viral evolution continue to interact, experts say year-round surveillance, stronger vector control, improved urban planning, and greater public awareness will be essential to limiting future outbreaks.
