Researchers have discovered significant changes in the life cycle and behaviour of Aedes mosquitoes, which carry the dengue fever virus.
Previous beliefs about their breeding grounds and biting patterns have been challenged, indicating a new challenge in combating these disease-carrying mosquitoes.
The study, conducted by Dr Kabirul Bashar, a professor of Zoology at Jahangirnagar University, revealed that Aedes mosquitoes can now breed in various types of water, including rainwater, saltwater, drain water, and sewage water.
The research also showed that the mosquitoes are now biting at night, in addition to their previous daytime biting behaviour. These changes have implications for mosquito control efforts.
The study, titled “Adaptation of Aedes aegypti mosquito larvae in Sewerage, sea, brackish, and drain water: A New Challenge for Dengue Control,” was conducted from 2021 to 2023. Dr Bashar highlighted these findings while speaking to Dhaka Tribune.
Surprisingly, evidence of Aedes mosquito breeding was even found in just one centimetre of accumulated water.
Additionally, the eggs of the Aedes mosquito can survive for six to nine months and hatch into larvae when they come into contact with even a small amount of water.
While Aedes mosquitoes were previously known to primarily bite during the day and early evening, new research indicates that they now also bite at night, albeit with lower biting rates.
Highly adaptable creatures
The study involved the examination of 134,904 mosquitoes collected from various areas, including Jahangirnagar University, Chittagong, and Cox's Bazar.
The mosquitoes were observed to be equally active between 4pm and 9pm, indicating sustained activity throughout the evening.
The research involved capturing mosquitoes on mosquito nets, trapping them in cups while rendering them unconscious with chloroform, and subsequently conducting species confirmation tests in the laboratory.
Dr Bashar explained that there are more than 3,000 species of mosquitoes worldwide, with 123 species found in Bangladesh.
Despite their small size, mosquitoes are highly adaptable creatures that can thrive in any environment and adjust accordingly.
Even Singapore, known for its cleanliness, has experienced recent dengue outbreaks.
The researcher attributed the mosquito's adaptation process to global urbanisation, much of which is unplanned.
The research identified 52 breeding sites, including unexpected locations such as parking lots and narrow channels near building entrances, where Aedes mosquitoes have been found to breed. Additionally, mega-construction sites have become breeding grounds for mosquitoes.
The dengue outbreak near the Rooppur nuclear power plant serves as a prime example.
Dr Bashar also highlighted the issue of light pollution, noting that the increased use of bright artificial lights in cities has contributed to changes in mosquito behaviour.
Highlighting the significance of mosquito behaviour and control, Dr Bashar emphasised the need for extensive research in these areas.
He went on to explain that the four different but closely related Flaviviridae family viruses (DENV-1, DENV-2, DENV-3, and DENV-4) are what cause dengue.
Infection with one stereotype does not provide immunity against the others, and subsequent infections with different stereotypes can be life-threatening.
Due to the viral nature of dengue, there is currently no specific treatment or vaccine available, making its control challenging.
The researcher suggested discontinuing the old and ongoing methods of mosquito control.
He emphasised the necessity of year-round research on mosquito control and conducting control activities accordingly.
It is crucial for various local and national authorities, such as union parishads, upazilas, districts, municipalities, and city corporations, to cooperate in implementing mosquito control measures based on research findings.
Efforts should be made to conduct door-to-door activities and raise public awareness, as mosquito control can only be successful when people are aware and proactive. This awareness should be spread rapidly before mosquitoes become an even greater threat.
Three key approaches
According to Dr Lelin Chowdhury, a public health expert and the director of Health and Hope Specialized Hospital, the Aedes aegypti mosquito, which used to primarily inhabit houses, has now spread dengue to towns and villages beyond urban areas since 2019.
This shift is a matter of concern, as dengue has now spread to 63 districts across the country.
Dr Chowdhury noted that Aedes mosquitoes now lay eggs and breed in both clean and dirty water, contributing to the rapid spread of mosquitoes and the disease.
Additionally, wild mosquitoes, along with resident mosquitoes, have become dengue carriers.
The mosquitoes, which used to bite during specific times of the day, now exhibit continuous biting behaviour, further exacerbating the issue.
Dr Chowdhury emphasised three key approaches to preventing dengue: destroying Aedes mosquito breeding grounds, killing adult mosquito larvae, and providing treatment to dengue patients.
The main treatment for dengue patients is supportive management, as there is currently no specific medicine or vaccine available for the viral disease.
Supportive management involves replenishing the fluids and water lost by the patient's body and maintaining a controlled fever. Nutritious food should be provided, and if the patient's condition deteriorates or platelet counts decrease, a hospital referral becomes necessary.
City corporations adapting strategies
The acting chief health officer of Dhaka South City Corporation (DSCC), Dr Fazle Shamsul Kabir, shed light on the revised mosquito control measures implemented by the city corporation.
A technical committee regularly reviews the evolving patterns of mosquitoes and their breeding sites, with Dr Kabir actively participating in the committee's discussions.
Recommendations from the committee guide the determination and application of appropriate pesticides. The committee ensures that the timing and nature of mosquito control activities are aligned with the suggested measures.
Dr Kabir highlighted how urbanisation has affected the behaviour of Aedes mosquitoes, blurring the line between day and night in their perception of the environment. In response, the city corporation has adapted its strategies to tackle these evolving patterns and implement effective measures.
The city corporation employs larviciding in the morning to eliminate mosquito larvae and adulticides in the afternoon to target fully grown mosquitoes. The morning insecticide used is called Temifs, while deltamethrin and malathion are applied in the afternoon.
Dr Kabir acknowledged the sadness associated with the current peak season for dengue cases.
He also highlighted that, compared to other countries such as Malaysia, the Philippines, Bangkok, and Indonesia, the number of dengue cases in Bangladesh is relatively lower.
The city corporation is working hard to keep the situation under control and prevent it from spiralling out of control.
Although completely eradicating the number of dengue cases is a challenging task, efforts are being made to bring the number closer to zero through determined actions and initiatives.
