High levels of Aedes larvae in Dhaka, higher outside

The breeding of Aedes mosquitoes inevitably raises the risk of dengue transmission, and signs of that are already evident at the start of the monsoon season.

Government and independent surveys have detected high concentrations of larvae of the dengue-carrying mosquito across both Dhaka city corporations.

However, the situation appears even more concerning in the country's south-eastern and southern regions, where several districts have recorded higher Aedes larval densities than the capital.

With the onset of the monsoon, the number of dengue patients has also begun to rise across Bangladesh.

According to the Directorate General of Health Services (DGHS), the country recorded nearly 6,000 dengue cases by 29 June this year.

Of those, 2,727 infections were reported in June alone, meaning that almost half of this year's total cases were identified during the month.

June has also recorded the highest death toll of the year, with 13 fatalities, including five deaths within the most recent 24-hour reporting period.

Experts say this marks only the beginning of the seasonal increase in dengue transmission.

They warn that the situation could deteriorate significantly unless authorities and the public take preventive measures immediately.

According to public health expert Professor Benazir Ahmed, Bangladesh can no longer regard dengue as a problem confined to Dhaka.

During the latest mosquito surveillance conducted by Dhaka North City Corporation between 12 and 16 June, officials found alarming concentrations of larvae at breeding sites, including flowerpots, plastic containers, basements, drains, water tanks and bottles.

Density of larvae in Dhaka is risky

Authorities measure the density of Aedes mosquito larvae using the Breteau Index (BI). If inspectors find Aedes larvae or pupae in 20 or more out of every 100 potential breeding sites, they classify the mosquito density as reaching a "high-risk" level.

During the latest mosquito surveillance conducted by Dhaka North City Corporation between 12 and 16 June, officials found alarming concentrations of larvae at breeding sites, including flowerpots, plastic containers, basements, drains, water tanks and bottles.

Surveys in five high-risk areas of the city recorded Breteau Index values ranging from 20 to 73.33, with an average BI exceeding 40.

However, Brigadier General Imrul Kayes Chowdhury, chief health officer of Dhaka North City Corporation, does not believe the situation has yet reached a critical stage.

He said, "We have found a high presence of larvae. However, environmental conditions have not yet allowed them to develop into mosquitoes on a large scale. Nevertheless, that risk remains."

In Dhaka South City Corporation's pre-monsoon survey, 63 of its 75 wards recorded Breteau Index values above 20. Among them, officials identified 27 wards as "extremely high-risk".

Situation outside Dhaka more alarming

During the final week of May, a team led by Professor Kabirul Bashar, an entomologist from the Department of Zoology at Jahangirnagar University, surveyed mosquito larvae in Cox's Bazar, Barishal, Barguna and Pirojpur districts.

The survey found exceptionally high larval densities in Cox's Bazar, particularly in the Rohingya refugee camps.

Professor Kabirul Bashar said, "The Breteau Index ranged from a minimum of 45 to a maximum of 92 in Cox's Bazar. This presents a very alarming picture."

The survey recorded an average Breteau Index of 43 in Cox's Bazar, 34 in Barishal and 43 in Pirojpur. A separate survey conducted by Chattogram City Corporation found an average Breteau Index of approximately 31 across Chattogram city.

“Epidemiological Triangle” remains intact as weather conditions favour dengue

Professor Kabirul Bashar explains the spread of dengue using what he describes as the "epidemiological triangle".

The three corners of this triangle represent the infected person, the mosquito and the environment, while the centre represents the dengue pathogen. When all four elements remain favourable simultaneously, the virus spreads rapidly.

Professor Kabirul Bashar said, "At present, none of the components of this triangle has been effectively disrupted. Infected people are present, mosquitoes are present, environmental conditions are favourable, and the pathogen is circulating. As a result, the risk of increasing transmission remains."

Professor Benazir Ahmed, public health expert Dengue has now become a nationwide disease. However, we have yet to recognise that reality. Most of our response remains centred on Dhaka, while district and upazila-level interventions are not receiving the attention they require.

Experts also believe that this year's weather is creating favourable conditions for a more severe dengue outbreak.

Bangladesh received more than 75 per cent above-average rainfall in April, an unusually high amount before the onset of the monsoon.

Meteorologist Bazlur Rashid said that prolonged, uninterrupted rainfall is unlikely during this year's monsoon. Instead, the country is more likely to experience intermittent rainfall accompanied by high temperatures.

According to experts, such weather provides ideal breeding conditions for Aedes mosquitoes.

Continuous heavy rainfall often washes away mosquito larvae, whereas intermittent rainfall allows water to accumulate in containers, creating ideal breeding sites for Aedes mosquitoes.

Barishal division faces elevated risk

Dengue was once regarded as a disease largely confined to Dhaka. That situation has now changed.

According to the Directorate General of Health Services (DGHS), Dhaka Division has recorded the highest number of dengue cases so far this year, with 2,093 infections. Of these, 1,361 cases have been reported in Dhaka Area alone.

According to the Directorate General of Health Services (DGHS), Dhaka Division has recorded the highest number of dengue cases so far this year, with 2,093 infections. Of these, 1,361 cases have been reported in Dhaka Area alone. Barishal Division has recorded 1,587 cases. The district-wise breakdown includes 383 cases in Barishal, 391 in Pirojpur, 304 in Jhalokathi, 272 in Patuakhali and 161 in Barguna. No other division has recorded more than 100 cases across as many districts as Barishal.

Barishal Division has recorded 1,587 cases. The district-wise breakdown includes 383 cases in Barishal, 391 in Pirojpur, 304 in Jhalokathi, 272 in Patuakhali and 161 in Barguna. No other division has recorded more than 100 cases across as many districts as Barishal.

So far this year, Chattogram Division has reported 1,116 dengue cases, including 357 in Chattogram District and 141 in Cox's Bazar. Authorities have also recorded 181 cases in Khulna, 242 in Bagerhat and 242 in Cumilla.

Bangladesh must move beyond “Dhaka-centred” approach

According to public health expert Professor Benazir Ahmed, the greatest challenge in tackling dengue lies in the gap between the reality of the outbreak and the country's level of preparedness.

He said, "Dengue has now become a nationwide disease. However, we have yet to recognise that reality. Most of our response remains centred on Dhaka, while district and upazila-level interventions are not receiving the attention they require."

Professor Benazir Ahmed advised the authorities to pay particular attention to the Barishal region.

Experts warn that dengue transmission will continue to increase unless authorities immediately eliminate mosquito breeding sites, strengthen surveillance at the local level and implement coordinated control measures nationwide.