Aedes mosquito surge raises fears of major dengue outbreak

A group of researchers has been conducting daily house-to-house inspections across Dhaka city in search of Aedes mosquitoes. Their two-week survey, conducted before the Eid-ul-Azha holiday, revealed that Aedes mosquito larvae were found in 7 to 8 out of every 15 houses. Aedes mosquitoes are the primary carriers of the dengue virus.

The most critical aspect of the larval survey is measuring larval density, typically assessed using the Breteau Index (BI). A BI score above 20 is considered alarming. According to the latest survey, the index currently ranges between 50 and 60 — a highly concerning level.

The survey was led by Professor Kabirul Bashar, an entomologist from the Department of Zoology at Jahangirnagar University. He told Prothom Alo, “This time, the breeding rate of Aedes mosquitoes is very high. There is a consistent trend of high mosquito density. If effective control measures are not implemented immediately, the dengue situation could become very serious.”

Professor Kabirul Bashar also noted that the incidence of Aedes mosquitoes is increasing at a similar rate in areas of both the north and south city corporation. He added that the number of dengue cases reported so far this year is significantly higher than during the same period last year.

Experts warn that the current conditions are “ideal” for a surge in dengue infections. They cite weather patterns, inaction by local government bodies, and above all, inadequate government preparedness as key contributing factors.

As of Monday ( 9June), a total of 4,977 people have been hospitalised with dengue across the country this year, and 23 people have died. In comparison, during the same period last year, there were 3,031 cases and 37 deaths.

The highest number of dengue infections in Bangladesh occurred in 2023. As of 8 June that year, 2,854 people had been infected and 21 had died. By the end of 2023, 321,179 people had contracted dengue, and 1,705 had died — the highest annual toll since the country began experiencing dengue outbreaks in 2000.

Touhid Uddin Ahmed, former chief scientific officer at the Institute of Epidemiology, Disease Control and Research (IEDCR), believes current weather conditions indicate a strong possibility of a major outbreak.

He told Prothom Alo yesterday, “There’s intermittent rainfall followed by intense heat. These are perfect conditions for Aedes mosquito breeding and dengue transmission.”

In May, Bangladesh received 63 per cent more rainfall than normal this year. This month too, intermittent rain and another heat wave are creating optimal conditions for mosquito breeding. Forecasts suggest rainfall may increase further in the coming week, with a low-pressure system developing in the ocean once again.

Nazmul Haider, a Bangladeshi researcher of mosquito-borne diseases at Keele University in the UK, explained that temperatures between 28 and 30 degrees Celsius are ideal for Aedes mosquito reproduction. He noted that in May, temperatures in Dhaka remained relatively low while intermittent rainfall persisted — conditions highly conducive to Aedes breeding.

It is not just Aedes mosquitoes that are spreading rapidly. Culex mosquitoes have also multiplied this year, particularly in the capital. In March, Professor Saifur Rahman, an entomologist at the National University, conducted a study on mosquito density in Gulshan, Dhaka. His findings revealed that between 900 and 2,000 mosquitoes were present in the area within 24 hours.

“This is highly unusual,” said Professor Saifur Rahman. “Finding even 200 mosquitoes in 24 hours is rare. Normally, Culex mosquitoes decline after the Boishakhi storms in April, but this year both Culex and dengue cases are rising. The current weather conditions are highly favorable for dengue transmission. Unfortunately, there is no visible action from city corporations or municipalities.”

This year, dengue infections are notably higher outside the capital than within. Dhaka’s two city corporations account for only 25 per cent of the country’s total dengue cases. The highest infection rate is currently in Barisal Division, which has reported 1,994 cases. In Dhaka South City Corporation, infections have risen from 602 last year to 777 this year. In Dhaka North, the number has increased from 438 to 469.

Speaking to Prothom Alo, Zillur Rahman, Chief Executive Officer of Dhaka South City Corporation, acknowledged the rise in cases. “The number of infections may increase, but we are prepared to control the situation. We have a dedicated budget. Our activities were paused during the Eid holidays but will now resume at full scale.”

However, entomologist Touhid Uddin Ahmed expressed skepticism about the city corporations’ efforts. “Looking at the current patient numbers and mosquito density, it’s clear that local government institutions — starting from the city corporations — are not taking effective action. Previously, some activity was at least visible. Now, there’s none. If immediate measures are not taken, the dengue situation could spiral out of control,” he warned.