Excessive rainfall across Bangladesh is increasing the risk of an early dengue outbreak this year, prompting entomologists to call for immediate government action to eliminate mosquito breeding sources and strengthen public awareness campaigns.
Bangladesh recorded 76 millimetres more rainfall in April compared to the seasonal average, with the trend continuing into May, according to meteorologist Bazlur Rashid.
The Bangladesh Meteorological Department (BMD) has forecast rain in parts of Rangpur, Rajshahi, and Dhaka divisions and at one or two places in the Khulna, Barishal, and Chattogram divisions, and moderately heavy to heavy rainfall in parts of Mymensingh and Sylhet until May 23.
Entomologists warned that early rainfall has already created mosquito breeding grounds across the country, and failure to act quickly could trigger a major dengue outbreak this year.
According to the DGHS, at least five dengue patients have died, and 2,963 have been hospitalised this year as of May 19.
“We are working in 13 districts of Bangladesh from Jahangirnagar University. Based on observations over the last 13 days, we can roughly say that in urban areas across the country, the Breteau Index has crossed 20,” said entomologist Kabirul Bashar, professor at Jahangirnagar University.
“While it is not extremely high, the index is significantly higher in many upazila-level areas where urbanisation has expanded. This trend is visible nationwide,” he added.
A Breteau Index (BI) of 20 means 20 water-holding containers with Aedes mosquito larvae were found per 100 houses inspected. The indicator is widely used by the World Health Organization and public health authorities to assess mosquito density and dengue risk. A BI of 20 is considered a warning threshold, indicating increased potential for dengue transmission.
“Source management remains the top priority. All water-holding containers that can serve as breeding sites must be removed. The peak season is approaching, so preparedness must begin immediately,” Bashar said.
He noted that rainfall leads to water accumulation in discarded containers, creating ideal breeding conditions for Aedes mosquitoes.
“When it rains, water collects in scattered containers, creating ideal breeding grounds for Aedes mosquitoes. Waste management must be strengthened to prevent water accumulation,” he said.
Bashar said this period is crucial for preventive action, especially through better solid waste management and removal of containers in rain-prone areas.
Expressing concern ahead of the upcoming Eid holidays, he urged residents to take preventive measures before leaving home.
“Any place where water can accumulate must be emptied. No container should be left exposed where rainwater can collect, as it can become a breeding site for Aedes mosquitoes,” he said.
He also advised covering drains, toilets and other water-retaining areas and properly managing plant pots and flower tubs. He added that insect growth regulators such as Novaluron and microbial insecticides like Bacillus thuringiensis israelensis (Bti) or Pyriproxyfen may also help suppress mosquito breeding.
Entomologist GM Saifur Rahman, associate professor at the National University, said identifying breeding sites is the first step toward long-term control.
“Once breeding sites are identified, Bti should be applied. Mosquitoes hatch when water accumulates in containers or stagnant areas, and Bti can destroy the larvae,” he said.
He added that, given current temperatures, mosquito larvae could mature within a week after rainfall.
Saifur recommended assessing mosquito density, identifying hotspots, and establishing a dedicated mosquito control cell for logistics, equipment, insecticide management and field operations.
“Immediate action is very important to control Aedes mosquitoes this year, otherwise we may see another dengue surge,” he warned.
