A study published in Pest Management Science revealed that insecticide resistance has severely undermined efforts to control the Aedes aegypti mosquito—the main vector of dengue fever in Bangladesh.
The research, conducted by an international team of scientists, highlights the urgent need for sustainable and effective strategies to curb the growing burden of dengue in the country.
Dengue fever is a major public health concern in Bangladesh, where the absence of effective drugs or widely available vaccines makes vector control essential.
However, despite the implementation of insecticide-based interventions, the country witnessed its worst dengue outbreak in 2019, with over 101,000 hospitalized cases. The study suggests the presence of high levels of insecticide resistance in Ae. aegypti population may have contributed to the growing burden of dengue.
The research team, led by Hasan Mohammad Al-Amin, a Ph.D. student under the supervision of Associate Professor Gregor Devine at the Mosquito Control Laboratory, QIMR Berghofer Medical Research Institute, Australia, investigated the intensity and mechanism of resistance to commonly deployed insecticides in Dhaka, the capital city of Bangladesh.
Their findings revealed that Dhaka Ae. aegypti colonies show extremely high levels of resistance to pyrethroids, a class of insecticides commonly used to target mosquito species. The research forms part of Al-Amin’s Ph.D. project.
Speaking at SCI about the implications of this resistance for dengue control, Dr. Devine said, “The use of pyrethroids in Dhaka is no longer effective, and the control program must move to another method.”
The guideline published in 2016 by the World Health Organization (WHO) recommends that when resistance to an insecticide is confirmed, the intensity of resistance must be determined. To make this recommendation, the team exposed mosquito samples to higher doses of insecticides and monitored the mortality rate—using a technique known as the CDC bottle bioassay.
“These doses do not correspond to the recommended rates in the field. However, they provide a comparative measure of the strength of the resistance and help determine if the effectiveness of the insecticide in the field is likely to be compromised,” explained Al -Amen.
To examine the real-world implications, researchers exposed free-flying mosquitoes from colonies in Dhaka to standard applications of pyrethroid aerosols at WHO-recommended rates in an experimental free-flight. room where mosquitoes can show their natural behavior. A large proportion (up to 74%) of mosquitoes survived the exposure.
Speaking about the results of the study, Al-Amin commented, “The level of insecticide resistance of Dhaka Ae. aegypti determined in my bioassay experiments undoubtedly compromises the operational control of Ae. aegypti in the city. This is highlighted by my experiments with free-flying mosquitoes under semi-field conditions, and the demonstration of significant survival after exposure to household and public health formulations.”
The researchers established that this resistance developed as a result of point mutations in the nerve cells of Ae. aegypti, which is the target area of pyrethroid insecticides. Explained by Dr. Devine, “Because of the mutations, the insecticides cannot bind to the target area and the mosquitoes remain protected.” The team also found a metabolic mechanism of resistance where certain enzymes detoxify insecticides in mosquitoes.
The study serves as a wake-up call for policymakers, public health officials, and control programs to work together to develop comprehensive and sustainable methods to overcome insecticide resistance and effectively control Dengue vectors in Bangladesh.
However, Al-Amin said the new strategies will take time to implement:
“Understandably, a considerable time is needed to adopt a different intervention. In this interim period, we recommend the use of a non-pyrethroid insecticide class for mosquito control.”
Possible alternatives include the insecticides malathion and bendiocarb, which qualify for use as outdoor spray and indoor residual spray, respectively. Finally, a non-insecticidal approach is needed to control Aedes-borne diseases in Bangladesh.
One possible way is to deliberately infect Ae. aegypti with Wolbachia bacteria, which has been shown to significantly reduce dengue transmission. As part of his thesis, Al-Amin did this for an Ae. aegypti strain from Dhaka and showed its virulence and virus control capabilities. This work is in preparation for peer-review and publication.
Al-Amin explained, “Ultimately, the implementation of a scalable and sustainable non-insecticide-based approach such as the release of mosquitoes infected with Wolbachia disease is necessary for the management of dengue.”
Hasan Mohammad Al‐Amin et al, Insecticide resistance compromises control of Aedes aegypti in Bangladesh, Pest Management Science (2023). DOI: 10.1002/ps.7462
Given by the Society of Chemical Industry
Citation: Insecticide resistance is compromising control programs against dengue fever in Bangladesh, study shows (2023, July 18) retrieved on July 19, 2023 from https://phys.org/news/2023 -07-insecticide-resistance-compromising-dengue-fever. html
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