Despite spending around Tk 825 crore on mosquito control over the last 11 years, Dhaka’s two city corporations have failed to prevent recurring outbreaks of dengue and other mosquito-borne diseases.

Dhaka North City Corporation spent nearly Tk 549.50 crore on pesticides, clearing weeds and water bodies, and purchasing equipment, while Dhaka South City Corporation spent around Tk 275.35 crore on similar activities.

This year, DNCC has proposed Tk 142 crore and DSCC Tk 58 crore for mosquito control, according to the budgets of the two city corporations.

Yet dengue continues to spread.

The problem is even more serious outside Dhaka, where most municipalities and local government bodies lack effective year-round systems to monitor Aedes mosquitoes and eliminate breeding sites.

Health officials also acknowledge that many dengue patients treated in Dhaka come from outside the capital.

According to the Directorate General of Health Service, at least 141 dengue patients died while 49,220 were hospitalised as of Friday since January. Of them, 77 deaths and 37,250 cases were reported outside Dhaka.

However, DGHS data currently cover only 139 hospitals, while around 20,000 hospitals, clinics and diagnostic centres are registered across the country.

Eleven of the 12 city corporations across the country do not have any entomologists to help authorities control mosquito-borne diseases, exposing a major weakness in efforts to combat dengue, which has become a year-round concern.

Moreover, civil surgeon offices in only 26 districts have approved posts for entomologists, while 40 other districts do not have any such posts. Of the 24 districts with approved posts, at least six have remained vacant for years.

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Experts say repeated fogging, larviciding and occasional cleanliness drives have failed because mosquito control is not being carried out through a comprehensive, science-based system.

Entomologist GM Saifur Rahman of National University said Bangladesh needs a dedicated integrated vector-management system led by trained entomologists.

He pointed to Kolkata as an example of a more systematic approach, where entomologists monitor mosquito populations throughout the year, identify clusters and determine the appropriate intervention for each location.

In Bangladesh, the process should begin with baseline surveys. A sample of houses should be inspected to determine whether mosquitoes are present. If mosquitoes are found in one house, surrounding premises should be checked to establish whether a cluster exists. The area should then be assessed against dengue cases.

“If dengue patients are being reported, that becomes a red cluster,” Saifur said. If cases continue to rise, the cluster becomes active and stronger interventions are required.

An entomologist should then determine whether fogging, larviciding, source reduction or another intervention is appropriate. Post-intervention surveillance should establish whether the measure worked. If it did not, a different approach should be adopted.

“This continuous monitoring and assessment” is essential, he said, but Bangladesh currently lacks such a coordinated system.

A centralised surveillance system could show where mosquito-control measures are working, where they are failing, how many clusters have been controlled and where dengue patients are coming from. Without such information, authorities largely respond after cases appear rather than prevent transmission.

Saifur also suggested bringing all dengue patients under a system similar to the one used during Covid-19. If every case were reported, authorities could investigate the patient’s home and surrounding area, including a radius of around 400 yards, to target both larvae and adult mosquitoes.

The DGHS, which usually conducts three Aedes surveys every year, also failed to conduct its regular nationwide survey this year.

Until 2024, the DGHS conducted three annual entomological surveys -- pre-monsoon, monsoon and post-monsoon -- to detect Aedes larvae in the two Dhaka city corporations. The surveys were conducted under the Communicable Diseases Control Programme of the fourth Health, Population and Nutrition Sector Programme (HPNSP), which expired in June 2024.

The interim government later cancelled the proposed fifth HPNSP, creating a funding gap. Although all three surveys were conducted in 2024, the DGHS could not conduct any last year due to a funding crisis, officials said. IEDCR conducted a pre-monsoon survey last year, but neither agency has planned one this year.

This year, DSCC conducted a small-scale pre-monsoon survey, while the DGHS Rajshahi division conducted a survey in August. However, no effective nationwide survey is being conducted despite significant dengue cases and deaths being reported outside Dhaka since 2019.

Prof Kabirul Bashar, an entomologist at Jahangirnagar University, said another fundamental problem is that authorities often use the same control methods for different mosquito species.

“Culex and Aedes mosquitoes are not controlled in the same way,” he said. Culex mosquitoes commonly breed in drains and polluted water, while Aedes mosquitoes frequently breed in small water-holding containers close to human habitation.

Surveys conducted by JU recently found that around 70 percent of Aedes breeding in Dhaka was concentrated in a handful of locations. More than 20 percent was associated with basements and car parks, around 19 percent with drums and buckets used to store water in and around homes, and another 7-8 percent with water meters and their associated pipes.

“So, if you look at drums, buckets, basement parking areas and WASA meters, more than 60 percent of Aedes breeding is concentrated in these few places,” Bashar said.

Yet these are precisely the locations where conventional mosquito-control operations often have limited access. City corporation workers may not enter basement parking areas of high-rise buildings without permission. Drums and buckets are usually inside private homes, while control measures around water meters have not reached everywhere.

Fogging alone therefore cannot solve dengue. It mainly targets adult mosquitoes and provides temporary relief but does not remove eggs and larvae from breeding sites, Bashar said.

Public participation is equally important. Residents who store water should keep containers covered and, where necessary, empty and scrub them regularly.

Officials of the two Dhaka city corporations told The Daily Star that they begin Aedes-control drives and awareness programmes well before the rainy season.

They, however, said current manpower is insufficient to conduct fogging and larviciding properly because the areas under the city corporations have expanded significantly.

Jahanne Fedous Binte Rahman, chief health officer of DSCC, said DSCC has around 1,050 workers, including supervisors, for mosquito-control operations across its 75 wards.

The workforce is particularly stretched in newly expanded areas, where large wards can take six to seven days to cover. Residents often complain that workers visit only once a week.

She said efforts to destroy Aedes breeding sites and raise public awareness had been intensified amid the rise in dengue cases, adding that there was no shortage of insecticides or larvicides.

An official of DNCC said the corporation has around 1,130 workers involved in mosquito-control activities, although additional manpower may be needed following its expansion.

The official said a large number of dengue patients reported in Dhaka are actually from outside the capital.

“Around 20–25 percent of dengue patients admitted to Dhaka hospitals are from Dhaka and its peripheral areas and rest are from other districts,” he said.