ABSTRACT.
Aedes albopictus is a highly invasive mosquito species and a vector of human arboviral diseases including dengue, chikungunya, and Zika. There are no effective drugs or vaccines for the treatment or prevention of most of these diseases, so the primary option for disease prevention and control is to target mosquitoes, often using insecticides. Despite vector control efforts, cases of arboviral diseases are increasing in Bangladesh and it is important to understand if this escalation is associated with the presence of insecticide resistance in Aedes populations, including Ae. albopictus. The CDC bottle bioassays performed on Ae. albopictus from two districts in Bangladesh detected resistance to permethrin but susceptibility to deltamethrin, malathion, and bendiocarb. The detection of permethrin resistance is worrisome, since arbovirus vector control strategies in Bangladesh currently include the use of permethrin. Routine monitoring of the susceptibility status of key vector populations in Bangladesh will allow a better understanding of resistance trends, enabling the strengthening of control strategies.
Aedes albopictus (Skuse, 1894) is known as the Asian tiger mosquito and is one of the most invasive mosquito species in the world.1 This anthropophilic mosquito species is a potential vector of a number of important arboviruses including dengue, chikungunya, and Zika, which are common causes of fever syndromes globally.2 Although the cumulative burden is not well quantified, these diseases have an alarming impact on human health and economies.3 While the majority of infections are clinically asymptomatic or mild, these infections can also cause debilitating and undifferentiated febrile illnesses progressing to severe secondary or congenital disorders, resulting in long-term physical disability, cognitive impairment, or death.4
In Bangladesh, Aedes-borne arboviral infections are becoming increasingly the common causes of morbidity and mortality; large outbreaks of chikungunya and dengue occurring in 2017 and 2019 led to infections in thousands of people.5,6 Widespread distribution of both Ae. aegypti and Ae. albopictus throughout the country puts nearly the whole nation at risk of these diseases and further outbreaks.7,8
Effective drugs and vaccines are not available for most Aedes-borne arboviral diseases. Vector control is the principal strategy to prevent and control these diseases, relying heavily on the use of chemical insecticides, particularly from the pyrethroid class because of their high efficacy against mosquitoes and low toxicity to humans.9 In Bangladesh, mosquito control primarily focuses on the nuisance control of Culex quinquefasciatus in metropolitan/city corporation areas by thermal fogging using a combination of permethrin, prallethrin, and tetramethrin/bioallethrin, and malaria vector control in the hilly and border-belt areas, especially in the highly endemic southeastern districts using deltamethrin-based long-lasting insecticidal nets (LLINs) and selective indoor residual spraying with deltamethrin in some malaria hotspots.10,11 Recent arboviral disease outbreaks have resulted in strengthening Aedes control efforts by city corporations, but large-scale and longer term strategies are still under development.10
Data on insecticide resistance of important mosquito vectors are scarce for Bangladesh. To address this important topic, a study was conducted in 2017–2018 to survey the resistance status and resistance mechanisms of Aedes spp. in Bangladesh. Data on Ae. aegypti have been published elsewhere, which include strong resistance to permethrin as well as substantial resistance to deltamethrin and malathion, whereas complete susceptibility to bendiocarb.10 The aim of this short note is to present data arising from bioassays conducted on Ae. albopictus to understand its resistance status.
Using ovitraps baited with grass infusion, Aedes spp. eggs were collected from a variety of arboviral transmission settings across Bangladesh. However, Ae. albopictus eggs were found only in the Chittagong city corporation area (22°20′30.7″N, 91°46′54.3″E), which is a high-transmission setting, and in Rowangchhari subdistrict (22°10′49.0″N, 92°20′09.8″E) under Bandarban district, which is a rural area and a low-transmission setting for Aedes-borne arboviral diseases but a highly malarious area.
Eggs were shipped to the Emerging Infections and Parasitology Laboratory of the International Center for Diarrheal Disease Research, Bangladesh (icddr,b) for rearing. Aedes albopictus were separated from Ae. aegypti and F0-F2 3- to 5-day-old, non-blood-fed female Ae. albopictus were used in CDC bottle bioassays. The CDC-recommended diagnostic doses were used for the bioassays with four insecticides: permethrin, deltamethrin, malathion, and bendiocarb.10
Although Ae. albopictus was observed to be fully susceptible to deltamethrin, malathion, and bendiocarb, resistance was detected to permethrin in both sites (18.8–65.5% mortality) (Table 1).
Table 1.
Susceptibility (percent survival and individuals tested) status of Aedes albopictus in Chittagong and Rowangchhari, Bandarban
| Area | % Mortality (number exposed) | |||
|---|---|---|---|---|
| Permethrin | Deltamethrin | Malathion | Bendiocarb | |
| Chittagong city corporation (city areas only) | 18.8 (16)* | 100 (116) | Not tested | 100 (118) |
| Rowangchhari subdistrict (rural areas) | 65.5 (107) | 100 (112)† | 100 (114) | 100 (114) |
Only 16 mosquitoes tested.
Control mortality was 6.25%, therefore, % mortality was corrected using Abbott’s formula.14
Information on the insecticide resistance status of mosquitoes in Bangladesh is limited, and this report provides data on the susceptibility status of Ae. albopictus for the first time. Future studies should also investigate the intensity of permethrin resistance in Ae. albopictus in Bangladesh. Permethrin resistance in Ae. aegypti and Anopheles vagus was previously documented at high levels in recent studies in Bangladesh.10,11 Recent studies on Bangladeshi Ae. aegypti have shed light on several underlying resistance mechanisms. Increased activity of esterases and oxidases and a high frequency of the 1016Gly kdr allele in the voltage-gated sodium channel (VGSC) gene were associated with permethrin resistance in Ae. aegypti.10 Although an important limitation of this study is that biochemical and molecular analyses were not conducted, our findings remain important, as they are the only data available on Ae. albopictus insecticide resistance in Bangladesh. Recent studies in neighboring India indicated the role of detoxifying enzymes and possible kdr as important underlying resistance mechanisms in Ae. albopictus.12,13
The use of pyrethroid-based insecticides for mosquito control is long-practiced in Bangladesh. Local authorities in urban areas have used permethrin for many years without routine surveillance of susceptibility status. The findings reported here together with the previous findings of permethrin resistance in Bangladeshi Ae. aegypti indicate that permethrin is unlikely to be the optimal insecticide to use to control these vectors. As Bangladesh begins to implement routine insecticide resistance monitoring in Aedes spp., these results provide an important baseline resource for developing effective vector control strategies.
ACKNOWLEDGMENTS
icddr,b acknowledges with gratitude the commitment of CDC to its research efforts. icddr,b is also grateful to the Governments of Bangladesh, Canada, Sweden, and the United Kingdom for providing core/unrestricted support.
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