News Desk :
Dengue used to be a cause of pain for Bangladesh during the rainy season, but the disease is striking throughout the year now, says entomologist Kabirul Bashar who specialises in mosquitoes.
Along with the change in seasonal intensity of the disease, Aedes mosquitoes, mostly centred around urban areas like Dhaka, now spread the virus in villages nationwide as a result of urbanisation.
Forecasts based on initial findings suggest Bangladesh may suffer widespread dengue infections this year, Kabirul said, reports bdnews24.com In an interview, the zoology professor of Jahangirnagar University said a comprehensive long-term plan, which must include integrated pest management, was needed to curb the spread of the disease.
Last year, 62,382 people were hospitalised with dengue and 281 of them died after a lull amid restrictions over COVID-19. In 2019, the government recorded the highest number of cases in recent history, with over 100,000 hospitalisations. As many as 164 deaths were counted by the government that year.
The arrival of monsoon this year has also been accompanied by a spike in cases as 6,293 people have been hospitalised so far and 39 of them have died.
The rainy season was when dengue infections were at their peak as Aedes aegypti mosquitoes breed in clean stagnant water. Cases were few in winter, but that trend started to change over the past few years.
“It’s no longer the case that Aedes mosquitoes breed only in pooled-up rainwater. The period from November to February rarely sees rain, but Aedes mosquitoes were found in higher numbers towards the start of this year,” Kabirul said, citing data from a study in Dhaka.
“Dengue fever is now a year-round phenomenon and there’s a reason behind it as well. The urbanisation dynamics in Dhaka have shifted,” the entomologist said.
“Many multi-storeyed buildings have been built which have basements where cars are kept and washed, causing water to accumulate. Aedes mosquitoes were found in such spots.”
Water accumulating in buildings under construction and citizens stocking up water in drums and buckets are also breeding grounds for Aedes mosquitoes, he said.
In 2019, dengue cases were found all over the country. Kabirul said villages are also at risk because the disease may spread to all 64 districts this year as well.
“Every district is undergoing urbanisation and this has a connection to Aedes mosquitoes, which grow in number wherever there’s urbanisation.”
Kabirul, like all other experts, stressed that dengue could not be curbed by the government, state, city corporations or any authorities alone as awareness was key to cutting its risks.
“That’s because Aedes mosquitoes are born in water accumulated in different containers at homes and yards.
Such containers can be found in underground parking, a flower tub inside homes, places where air conditioners discharge water, and even a tyre lying in front of a home. Citizens must keep a keen eye out so these things don’t contain water.”
The city corporations would take care of roads, open structures, and government and private establishments. The authorities working in tandem with the citizens can curb dengue in the country, Kabirul said.
Dhaka experiences few dengue infections in some years, while the number is much higher at other times. Kabirul said it’s because of the nature of the virus’s carrier.
“It’s like a wave. The number of cases in 2020 was lower and it rose the following year before rising even higher in 2022.
“Our forecasting model based on data from the field shows that the dengue situation would be quite bad this year if we can’t rein it in right now.”
Kabirul said ‘integrated management’ was key to controlling Aedes mosquitoes.
The measures can be divided into four main steps, starting with environmental management, he said. It included changing the environment of the mosquitoes’ breeding grounds.
It involves simple measures like turning a container where water might accumulate upside down or keeping all drains flowing so that the mosquitoes cannot breed there.
The next point he brought up involved controlling Aedes mosquitoes with other creatures, like guppy fish, which eat mosquito larvae, or dragonflies, which are known for eating mosquitoes.
Insecticides were also a prime method of removing these mosquitoes. He also brought up involving the citizens in anti-dengue measures as the fourth step.
“If we want to control the Aedes mosquito population and dengue, we have to come up with a 10-year masterplan, of which integrated mosquito management would be a key part. Otherwise, it would be very difficult to achieve.”
Kabirul mentioned that encouraging donor organisations, like the World Bank or the World Health Organization, to prioritise mosquito control would help make headway in taking up the plan.
Controlling the fertility of mosquitoes by using a bacteria called Wolbachia is also being discussed but it requires further studies, Kabirul said.
Inserting the bacteria into a male mosquito renders it incapable of breeding.
“When it gets together with a female mosquito after being released, the eggs would not give birth to larvae. That’s one way of establishing control.”
But this method has different limitations, he said. “It will be challenging for the mosquito sterilised in a lab to survive in a polluted megacity like Dhaka.”
He said the process needs to be experimented further in controlled environments first.
