Keywords
Anopheles; Malaria Elimination; Vector Control Program; Insecticide Resistance; Asian Countries
Anopheles; Malaria Elimination; Vector Control Program; Insecticide Resistance; Asian Countries
Malaria is one of the most common vector-borne diseases widespread in the tropics and subtropics1. According to the World Malaria Report (2019), an estimated 219 million cases were recorded in 2017, compared to the 217 million in the previous year2. The global estimate of deaths caused by malaria reached 435,000 cases, which was the same number in 20163. The use of insecticides is the basis for the effective control of vectors, and this process has played an essential role in the management and elimination of malaria4.
The prevention of malaria mainly depends on one class of insecticides, namely pyrethroids; however, the increase in resistance to it reduces this treatment's efficacy5. The progressive reduction of malaria's burden through substantial improvements of insecticide-based vector control in recent years is reversible by the emergence of widespread resistance to this chemical6. Insecticide resistance is widespread and is now reported in almost two-thirds of the countries with ongoing malaria transmission. This resistance affects all major vector species and groups of insecticides7.
Vector control is an essential aspect of a program organized to manage the disease transmitted by this type of organism. The use of insecticides for this process is an effective strategy; however, it is also related to the development of resistance in targeted vectors and is one reason for the failure of disease control in many countries8. Since 2000, malaria cases have halved due to the management and vector control interventions, estimated to have saved 660 million people9. The global commitment to eliminate malaria by 2030 requires immediate efforts that include the establishment of infrastructure for monitoring regular insecticide resistance, the development of combined and effective control products10.
This review aimed to determine the status of insecticide resistance in Asia and how to implement interventions. It is also expected that this sets an example for other countries in the vector control program and provides guidance for insecticides and malaria risk reduction.
This study retrieved articles from four science databases, namely ProQuest, Science Direct, EBSCO, and PubMed, from December 2009 to December 2019. A systematic review was conducted using a predefined protocol based on the preferred reporting items for systematic reviews and meta-analyses (PRISMA)11,12. The searching process utilized four main combinations of the following keywords: “malaria”, “vector control”, “insecticide”, and “Asia”. In order to reduce the risk of bias from the articles obtained, the researchers conducted disbursements in all databases using the same keywords and on the same day.
In ProQuest, “malaria” and “vector control”, as well as “insecticide”, were used as keywords. The full text, the source of an article, scholarly journal, Asia, and date of publication as in the last ten years were included in the filter. The search strategy and filter used in Science Direct were the same as that above except "Asia". In EBSCO, a similar keyword was also used. The limiters were the same as the filter in the Proquest, but also included "abstract available". In the Pubmed, the terms used were as follows, ("malaria"[MeSH Terms] OR "malaria"[All Fields]) AND ("vector"[MeSH Terms] OR "vector"[All Fields]) AND ("control"[MeSH Terms] OR "control"[All Fields]) AND ("insecticide"[MeSH Terms] OR "insecticide"[All Fields]) AND ("loattrfulltext"[sb] AND "2009/12/02"[PDat] : "2019/12/02"[Pdat])s.
Original articles (academic or research papers) in Asia, written in English and published in the last ten years were included. Study designs such as prospective study, review, cross-sectional, cohort, and case control were included. Articles about biochemical, resistance to dieldrin (RDL) mutation, knowledge and attitudes, and spatial modeling were excluded because that can cause different results. Articles about malaria but including nothing about insecticides were excluded. The implications of insecticide resistance in related countries were investigated. Studies that were not relevant to this study were excluded.
The articles' eligibility was determined from each title, abstract, and full text by two reviewers (DP and DS). DP and DS also independently screened the articles for inclusion and extracted data on general information. To solve any disagreements and problems during the study, regular meetings were held by the researchers to discuss issues.
The search strategy and inclusion and exclusion criteria were validated and implemented. The initial database was then created from the electronic search. All citations were first filtered by title and abstract, and duplicates omitted. The full texts of eligible papers were then obtained independently for further filtering. After resolving the differences in data extraction or interpretation through consensual discussions based on the inclusion and exclusion criteria mentioned above, the final papers were selected.
The data from the chosen eligible studies were the authors, study period, publishing year, the country where it was conducted, settings, location characteristics, bioassay methods, the sample of Anopheles mosquito, and the quartiles in SCImagoJR. SCImagoJR is a publicly available portal that includes the journals and country scientific indicators developed from the information contained in the Scopus database. The findings were arranged according to the objective and result obtained in related implications of malaria vector control resistance. Throughout the entire selection process, the use of insecticides in the bioassay method, the associated mortality rate of the Anopheles mosquito, and its implementation in the specific areas were reported to illustrate the practice's pattern and extent.
All variables for which we extracted data ware Anopheles species, vector habitat, bioassay method, insecticides, mortality rate, insecticide resistance strategies/intervention. The differences in methods could bias the results; to reduce this bias, we selected articles with a similar method. For articles about insecticide resistance, we only looked at articles using bioassay with the world health organization (WHO) standard13. The WHO bioassay is carried out with paper impregnated from four main classes of insecticides in common use, with different concentrations according to the WHO test procedure14.
The identification process for review is outlined in Figure 115. There were 1,408 articles retrieved during the initial searching (ProQuest=722, Science Direct=267, EBSCO=50, Pubmed=285 and Scopus=84). Through screening, 27 articles were excluded because of duplication, 1,361 based on title and abstract incompatibility and 20 due to inconsistency with the inclusion criteria; 15 were chosen to be analyzed.
The 15 eligible articles originated from eight Asian countries published from 2012 to 2019 journals are shown in Table 1.
Authors | Title | Publish | Country | Study periods | Publisher | Reference |
---|---|---|---|---|---|---|
Ahmad et al. | Status of insecticide resistance in high-risk malaria provinces in Afghanistan. | 2016 | Afghanistan | August to October 2014 | Malaria Journal | 24 |
Mishra et al. | Insecticide resistance status of Anopheles culicifacies in Madhya Pradesh, central India | 2012 | India | August to September 2009 | Journal of Vector- Borne Diseases | 8 |
Dhiman et al. | Insecticide resistance and human blood meal preference for Anopheles annularis in Asom-Meghalaya border area, northeast India | 2014 | India | June–August 2011 | Journal of Vector- Borne Diseases | 21 |
Sahu et al. | Triple insecticide resistance of Anopheles culicifacies: A practical impediment for malaria control in Odisha State, India. | 2015 | India | April to June 2014 | Indian Journal of Medical Research | 19 |
Chand et al. | Insecticide resistance status of An. culicifacies in Gadchiroli (Maharashtra) India | 2017 | India | August 2016 and February 2017 | Pathogens and global health | 25 |
Chareonviriyaphap et al. | Review of insecticide resistance and behavioral avoidance of human diseases by vectors in Thailand | 2013 | Thailand | 2000–2010 | Parasites & Vectors | 26 |
Chaumeau et al. | Insecticide resistance of malaria vectors along the Thailand-Myanmar border | 2017 | Thailand | August and November 2014, July 2015 | Parasites & Vectors | 20 |
Sumarnrote et al. | Insecticide resistance status of Anopheles mosquitoes in Ubon Ratchathani province, Northeastern Thailand | 2017 | Thailand | September 2013–September 2015 | Malaria Journal | 17 |
Gorouhi et al. | Biochemical Basis of Cyfluthrin and DDT Resistance in Anopheles stephensi (Diptera: Culicidae) in Malarious Area of Iran | 2018 | Iran | April–June 2015 | Journal of Arthropod-Borne Diseases | 22 |
Vatandoost et al. | Indication of pyrethroid resistance in the main malaria vector, Anopheles stephensi from Iran | 2012 | Iran | Spring 2011 | Asian Pacific Journal of Tropical Medicine | 27 |
Marcombe et al. | Insecticide resistance status of malaria vectors in Lao PDR | 2017 | Lao | The rainy (June to October) and dry (January to May) seasons of 2014 and 2015 | PloS One | 28 |
Qin et al. | Insecticide resistance of Anopheles sinensis and An. vagus in Hainan Island, a malaria-endemic area in China | 2014 | China | July–August 2012 | Parasites & Vectors | 29 |
Dai et al. | Development of insecticide resistance of malaria vector Anopheles sinensis in Shandong Province In China | 2015 | China | 2003–2012 | Malaria Journal | 30 |
Surendran et al. | Variations in susceptibility to common insecticides and resistance mechanisms among morphologically identified species of the malaria vector Anopheles subpictus in Sri Lanka | 2012 | Sri Lanka | July 2008–June 2010 | Parasites & Vectors | 31 |
S.İ. Yavaşoglu, et al. | Current insecticide resistance status of Anopheles sacharovi and A. superpictus in former malaria-endemic areas of Turkey | 2019 | Turkey | April 2014 and September 2015 | ActaTropica | 32 |
There were 23 species of Anopheles from these studies (Table 2). In several countries, the main vectors included An. stephensi (Iran), An. superpictus (Afghanistan), An. culicifacies (India), An. minimus and An. maculatus (Lao and Thailand), An. sinensis (China), An. subpictus (Sri Lanka), and An. sacharovi (Turkey). From Table 2, the malaria vector was divided into three habitats, based on distribution, namely in rice fields, forests and on the coast, and flowing rivers. The differences in the main vector of each country depended on environmental/ecological conditions, living habitat, as well as the feeding and resting behavior of each Anopheles.
Study location | Country | Anopheles species | Sample adult female mosquitos (n) | Vector habitat | Reference |
---|---|---|---|---|---|
Nangarhar, Laghman, Kunar, Ghazni, and Badakhshan | Afghanistan | An. stephensi, An. superpictus, An. culicifacies | 2049 | Ricefield, river stream, ponds, and water puddle | 24 |
Madhya Pradesh | India | An. culicifacies | NA | Forest | 8 |
Asom-Meghalaya border area, northeast India | India | An. annularis | 200 | Forest, ponds irrigation | 21 |
Rayagada, Nowrangpur, Kalahandi, Malkangiri and Koraput | India | An. culicifacies | 1740 | Forest | 19 |
Gadchiroli district | India | An. culicifacies | NA | Forest | 25 |
Chiang Mai-Chiang Dao, Mae Hongsom, Phrae | Thailand | An. minimus An. annularis | NA | Paddy fields and rivulet | 26 |
Thailand-Myanmar Border | Thailand | An. annularis, An. minimus, An. hyrcanus, An. barbirostris, An. vagus, An. maculatus, An. jamessi, An. scanloni, An. kochi, An. tesselatus | 5896 | Agriculture | 20 |
Khong Chiam, Sirindhorn, Buntharik, and Nachaluay | Thailand | An. hyrcanus, An. barbirostris, An. maculatus, An. nivipes, An. philipinensis, An. vagus An. dirus An. karwari | 2088 | Forest and ricefield | 17 |
Chabahar Seaport, southeast corner of Iran | Iran | An. stephensi | 317 | Seaport | 22 |
Sistan and Baluchistan | Iran | An.stephensi | 733 | Coastal | 27 |
Phongsaly, Bokeo, LuangPrabang, Vientiane Pro, Borlikhamxay, Khammouane, Savannakhet, Saravane, Sekong, Attapeu. | Lao | An. minimus, An. hyrcanus, An. vagus An. maculatus An. nivipes An. philipinesnis An. umbrosus An. kochi An. tesselatus An. aconitus | 3977 | Forest, village, agriculture | 28 |
Hainan Island | China | An. sinensis, An. vagus | 1468 | Mountainous and ricefield | 29 |
Shandong Province | China | An. sinensis | 4370 | Irrigated ricefield, aquatic habitat, and small ponds | 30 |
Batticaloa, Puttalam, Trincomalee and Ampara | Sri Lanka | An. subpictus An. sundaicus | 256 | Coastal and inland | 31 |
Southeastern Anatolia and the Mediterranean | Turkey | An. superpictus, An. sacharovi | 1230 | Agricultural, ponds, stream and swamps | 32 |
The entire female Anopheles collected was morphologically identified for their species or complexes using stereomicroscopes and morphological keys16. The mosquitoes were separated into groups of species, complexes, or bioassay, then kept alive by giving them a sugar solution17.
Anopheles mosquitoes were morphologically identified at the adult stage using the Glick identification key18. The susceptibility tests were carried out following the WHO guidelines for monitoring resistance in malaria vectors. From 15 papers reviewed, the impregnated with insecticides of DDT (4%), malathion (5%), bendiocarb (0.1%), propoxur (0,1%), deltamethrin (0.05%) and l-cyhalothrin (0.05%), cyfluthrin 0.15%, permethrin 0.75%, and etofenprox 0.5% was prepared by adopting the WHO standard method14 (Table 3).
The insecticide bioassay was then carried out using a recommended standard WHO kit13. The mortality rate was recorded 24 hours after exposure, while the average death was calculated for each insecticide and according to the WHO criteria19. Bioassay results were summarized in three resistance classes according to the WHO criteria12: (1) susceptible when death was 98% or higher, (2) resistance-possibility was tolerable when mortality was between 97% and 80%, and (3) resistant when death case was lower than 80%18.
The highest mortality rate (MR) ≥ 98% of etofenprox application was on An. stephensi in Iran. While permethrin application was on An. superpictus (Afghanistan), An. nivipes (Thailand), An. philipinensis (Lao and Thailand), and An. tesselatus (Lao). Then, bendiocarb and malathion were on An. culicifacies (India and Afghanistan). Also, deltamethrin was on An. anularis (India), An. barbirostris, An. dirus, An. karwari (Thailand), An. vagus (Thailand and China), An. maculatus (Lao and Thailand), and An. umbrosus (Lao). An minimus (Thailand Myanmar Border), Meanwhile, permethrin and deltamethrin were on An. aconitus, and An. kochi (Lao). Lastly, lambda cyalothrin and deltamethrin were on An. sundaicus (Sri Lanka), with MR ≤ 97% indicating resistance-possibility based on the WHO classification.
Table 4 shows the level of anopheles resistance to organochlorine (dichlorodiphenyltrichloroethane; DDT), organophosphate (malathion), carbamate (bendiocarb and propoxur), and pyrethroid (permethrin, deltamethrin, lambda cyalothrin, cyfluthrin, and etofenprox). Almost all the species of this mosquito studied were possibly resistant to DDT. Furthermore, this similar issue has been reported in An. stepensi, An. superpictus, An. culicifacies, An. vagus, An. sinensi, An. subpictus, and An. sachrovi to malathion. Also, it was found in An. superpictus and An. sachrovi to propoxur as well as in An. umbrosus to permethrin. The same was in An. sinensis, An. superpictus, An. sundaicus, An. minimus, An. maculatus and An. jamessi to deltamethrin. Resistance was also reported in An. stephensi, An. culcifacies, An. vagus, and An. barbirostris to permethrin and deltamethrin, and in An. stephensi to etofenprox. However, direct resistance was found in An. hyrcanus to Permethrin and deltamethrin, as well as in An. culicifacies to lambda cyalothrin. Also, this was found in An. stephensi, An. sinensis and An. culicifacies to cyfluthrin.
No | Anopheles species | Percentage of mortality (Susceptibility Status) | Reference | ||||||||
---|---|---|---|---|---|---|---|---|---|---|---|
Organochlorine | Organophosphate | Carbamate | Pyrethroid | ||||||||
DDT (%) | Malathion (%) | Bendiocarb (%) | Propoxur (%) | Permethrin (%) | Deltamethrin (%) | Lambda- cyhalothrin (%) | Cyfluthrin (%) | Etofenprox (%) | |||
1 | An. stephensi* | 31-60 (R) | 47-97 (R) | 87-100 (PR) | NA | 87-91 (PR) | 66-78 (R) | 24 | |||
45 (R) | NA | NA | NA | 92.3 (PR) | 96(PR) | 88.4 (PR) | 55 (R) | 91 (PR) | 27 | ||
62 (R) | NA | NA | NA | NA | 96 (PR) | 89 (PR) | 82 (PR) | 100 (S) | 22 | ||
2 | An. superpictus* | 50-86.7 (R-PR) | 61.7-88.3 (R-PR) | 68.3-91.7 (R-PR) | NA | NA | NA | NA | NA | 32 | |
100 (S) | 100 (S) | 92 (PR) | NA | 100 (S) | 85 (PR) | NA | NA | NA | 24 | ||
3 | An. culicifacies* | 6.6-26.6 (R) | 65.4-100 (R-S) | NA | NA | NA | 71.6-94.1 (R-PR) | NA | NA | NA | 8 |
11.4-15.3 (R) | 60.4-76.2 (R) | NA | NA | NA | 72.6-84 (R-PR) | NA | NA | NA | 19 | ||
37.1 (R) | 74 (R) | NA | NA | 91.3 (PR) | 83.8 (PR) | 59.9 (R) | 70.2 (R) | NA | 25 | ||
81 (PR) | 95 (PR) | 100 (S) | 89 (PR) | 64(R) | 24 | ||||||
4 | An. annularis | 11.9-28.3 (R) | NA | NA | NA | NA | 97.7-98.1(PR-S) | NA | NA | NA | 21 |
NA | NA | NA | NA | NA | NA | NA | NA | NA | 26 | ||
100 (S) | 20 | ||||||||||
5 | An. minimus* | NA | NA | NA | NA | NA | NA | NA | NA | NA | 26 |
NA | NA | NA | NA | NA | 92 (PR) | NA | NA | NA | 20 | ||
98-100 (S) | NA | NA | NA | 100 (S) | 100 (S) | NA | NA | NA | 28 | ||
6 | An. hyrcanus* | 57 (R) | NA | NA | NA | 48 (R) | 33 (R) | NA | NA | NA | 20 |
72-83 (R-PR) | NA | NA | NA | 65-87 (R-PR) | 45-85 (R-PR) | NA | NA | NA | 17 | ||
90 (PR) | NA | NA | NA | NA | NA | NA | NA | NA | 28 | ||
7 | An. barbirostris* | 69 (R) | NA | NA | NA | NA | 97-100 (PR-S) | NA | NA | NA | 17 |
74 (R) | NA | NA | NA | 84 (PR) | 72 (R) | NA | NA | NA | 20 | ||
8 | An. vagus* | 34-61 (R) | NA | NA | NA | 89-95 (PR) | 79-95 (R-PR) | NA | NA | NA | 28 |
67.1-88.8 (R-PR) | 77.3-88.9 (R-PR) | NA | NA | NA | NA | NA | NA | NA | 29 | ||
97 (PR) | NA | NA | NA | 95 (PR) | 75 (R) | NA | NA | NA | 20 | ||
NA | NA | NA | NA | NA | 97.9-100 (S) | NA | NA | NA | 29 | ||
NA | NA | NA | NA | NA | 100 (S) | NA | NA | NA | 17 | ||
9 | An. maculatus* | 86-100 (PR-S) | NA | NA | NA | NA | NA | NA | NA | NA | 28 |
NA | NA | NA | NA | 97 (PR) | 85 (PR) | NA | NA | NA | 20 | ||
NA | NA | NA | NA | NA | 100 (PR) | NA | NA | NA | 28 | ||
NA | NA | NA | NA | NA | 100 (PR) | NA | NA | NA | 17 | ||
10 | An. jamessi | NA | NA | NA | NA | NA | 87 (PR) | NA | NA | NA | 20 |
11 | An. nivipes | 0-100 (R-S) | NA | NA | NA | 90-100 (PR) | 100 (S) | NA | NA | NA | 28 |
NA | NA | NA | NA | 100 (S) | NA | NA | NA | NA | 17 | ||
12 | An. philippinenses | 33-100 (R-S) | NA | NA | NA | 100 (S) | NA | NA | NA | NA | 28 |
100 (S) | NA | NA | NA | 100 (S) | 100 (S) | NA | NA | NA | 17 | ||
13 | An. umbrosus | 63 (R) | NA | NA | NA | 86 (PR) | 100 (S) | NA | NA | NA | 28 |
14 | An. sinensis* | 30.4 (R) | 86.6 (PR) | NA | NA | NA | 35.8 (R) | NA | 32.4 (R) | NA | 30 |
72.7-78.4 (R) | NA | NA | NA | NA | 85.8-91(PR) | NA | NA | NA | 29 | ||
15 | An. subpictus* | 16-35 (R) | 49-69 (R) | NA | NA | NA | 82-96 (PR) | 72-97 (R-PR) | NA | NA | 31 |
16 | An. sacharovi* | 55-78.3(R) | 58.3-90 (R-PR) | NA | 68.3-90 (R-PR) | NA | NA | NA | NA | NA | 32 |
17 | An.scanloni | 84 (PR) | NA | NA | NA | NA | NA | NA | NA | NA | 20 |
18 | An.kochi | 82-100 (PR-S) | NA | NA | NA | 100 (S) | 100 (S) | NA | NA | NA | 28 |
NA | NA | NA | NA | NA | 98 (S) | NA | NA | NA | 20 | ||
19 | An.tessellatus | 14 (R) | NA | NA | NA | 100 (S) | NA | NA | NA | NA | 28 |
NA | NA | NA | NA | NA | 98 (S) | NA | NA | NA | 20 | ||
20 | An.sundaicus | 38-47 (R) | 93-98 (PR-S) | NA | NA | NA | 97-100 (S) | 100 (S) | NA | NA | 31 |
21 | An.aconitus | 100 (S) | NA | NA | NA | 100 (S) | 100 (S) | NA | NA | NA | 28 |
22 | An.dirus | NA | NA | NA | NA | 100 (S) | NA | NA | NA | 17 | |
23 | An.karwari | NA | NA | NA | NA | 100 (S) | NA | NA | NA | 17 |
Table 5 shows that insecticide resistance interventions in several Asian countries are through vector prevention by environmental, biological, and chemical management. Implementation is through insecticide rotation monitoring, mapping, and surveillance. Malaria eradication started from effective prevention, technical capability approaches, government and community support, funding sources, accurate data, and adequate implementation.
Country | Study location | Location characteristic | Insecticide resistance strategies | Reference |
---|---|---|---|---|
Afganistan | Nangarhar, Laghman, Kunar, Ghazni, and Badakhshan | Rice field, river stream, ponds, and water puddle | Establishing a management plan for insecticide resistance, and monitoring this situation in all malaria-endemic provinces. | 24 |
India | Madhya Pradesh | Forest | Resistance management strategy by appropriate rotation of different insecticides, including carbamates and incorporating a synergist with synthetic pyrethroids for treating mosquito nets for the control of malaria vectors in these areas. Periodical monitoring of susceptibility/ resistance status of different insecticides. | 8,19,21,25 |
Asom-Meghalaya border area, northeast India | Forest, ponds irrigation | |||
Rayagada, Nowrangpur, Kalahandi, Malkangiri and Koraput | Cattle sheds, human dwelling | |||
Gadchiroli district | Forest | |||
Thailand | Chiang Mai-Chiang Dao, Mae Hongsom, Phrae | Paddy fields and rivulet | Vector prevention strategies and monitoring insecticide resistance. Achieving universal coverage and proper use of LLIN for all people at risk of malaria. Alternative control tools (e.g., insecticide-treated clothes, spatial repellents, or treated hammocks) adapted to the situation of people's activities are more effective in reducing the malaria burden | 17,20,26 |
Thailand-Myanmar Border | Agriculture | |||
Khong Chiam, Sirindhorn, Buntharik, and Nachaluay | Forest and rice field | |||
Iran | Chabahar Seaport, southeast corner of Iran | Seaport | Biological, chemical, and environmental management. Rotation of insecticide. Monitoring and mapping of insecticide resistance in the primary malaria vector for the implementation of any vector control. Evaluation of the mechanisms and implementation of proper insecticide resistance management strategies. | 22,27 |
Sistan and Baluchistan | Coastal | |||
Lao | Phongsaly, Bokeo, LuangPrabang, Vientiane Pro, Borlikhamxay, Khammouane, Savannakhet, Saravane, Sekong, Attapeu. | Forest, village | Routine monitoring of the insecticide resistance levels and mechanisms to ensure effective malaria control. Use of insecticide with different modes of action, rotation, or combination in the same area. | 28 |
China | Hainan Island | Mountainous and ricefield | Cost-effective integrated vector control programs that are beyond synthetic insecticides. The genetic basis of insecticide resistance to implementing more effective vector control strategies. Monitoring the efficacy of common insecticide and exploring the molecular basis of resistance. | 29,30 |
Shandong Province | Irrigated ricefield, aquatic habitat, and small ponds | |||
Sri Lanka | Batticaloa, Puttalam, Trincomalee and Ampara | Coastal and inland | Monitoring genetically different vector populations and their sensitivity to varying insecticides. Developing simple molecular tools and techniques to differentiate morphologically similar anopheles species on the field. | 31 |
Turkey | Southeastern Anatolia and the Mediterranean | Agricultural, ponds, stream, and swamps | Effective management of insecticide resistance and monitoring of the status at a regular interval to prevent delay to its development. Integrated vector control strategies including biological, chemical, and physical strategies implemented in a combination | 32 |
Ecologically, the sites used were mountainous, harbor/seaport, mixed thicket/ lush and dense forests, humid climate, rivers, rice fields, and ponds that provide a suitable environment for vector mosquito breeding. Anopheles mosquitos' seasonal activity differs in various regions due to environmental conditions20. Also, those collected were identified for species based on their morphological characteristics19,21.
The application of chemical insecticides is one of the most critical interventions for malaria control, which included organochlorines (DDT, dieldrin, and BHC), organophosphates (pyrimytophos-methyl and malathion), carbamates (propoxur), and pyrethroids (lambda-cyhalothrin and deltamethrin). And were used in various forms of application, such as indoor residual spraying (IRS) and insecticide-treated mosquito nets (ITNS) for controlling adult mosquitos. In contrast, organophosphates for larviciding were used in malaria-prone areas22. Currently, the pyrethroids were used in various Asia countries for ITNs and long-lasting insecticidal nets (LLINs). They were also considered the most effective because of their advantages, namely low mammalian toxicity, rapid knockdown activity, and high efficacy against a wide range of insect pests, especially mosquitos22.
Resistance to various insecticide classes was a common problem in different malaria vector species. This situation has been reported and is shown in Table 5, including widespread resistance to DDT and pyrethroids23. The multiple resistance of reported malaria vector Included An. stephensi, An. superpictus, An. culinary, An.annularis, An. minimus, An. hyrcanus, An. barbirostris, An. vagus, An. maculatus, An. jamessi, An nivipes, An. philippinensis, An. umbrosus, and An. sinensis in Asia. Most of the new reports were towards pyrethroid compounds, the only insecticides used for LLINs22. This became a challenge for malaria control and elimination, therefore, using the same insecticide for multiple successive IRS cycles is not recommended; preferably a rotation system with various types of these groups, including carbamates, should be used33. The rotation should start with an insecticide that has the lowest resistance frequency. In high-coverage areas with LLINs, pyrethroids were good choices for IRS because this added to the selection pressure.
Furthermore, using an impregnated net synergistically with synthetic pyrethroid was a better choice for malaria vectors resistant to this class of chemical. The mixed nets, such as the aforementioned, have applications against resistible mosquitoes, mainly based on oxidative metabolism34. Since monitoring of the resistance was a critical element for implementing insecticide-based vector control interventions, there was a need for periodic surveillance at least once a year or preferably every six months13.
The mortality test category was in the range between 98–100%, 80–97%, and <80%, and was categorized as susceptible, possibly resistant, and resistant population, respectively23. All vectors had resistance to DDT with a value below 80%; however, the use of insecticide began to decline gradually over the last few decades and was removed entirely from malaria control in 2000. This decline was due to the perceived adverse effects on the environment and decreased public acceptance for spraying indoor residues35.
Pyrethroids were the most commonly used insecticides for ITN and IRS, which target indoor transmission and mosquitos that bite in the room29. The mortality rate was <80% for the pyrethroid group in An. vagus, An. culinary, An. stephensi, An. hyrcanus, An. barbirostris, An. superpictus, An. sacharovi, and An. subpictus. This proved that pyrethroid was less effective. Meanwhile, insecticide resistance was present in malaria vectors in Asia, and the genes spread rapidly throughout the world36.
The use of insecticides to reduce vector populations has become the main strategy for malaria control. Presently, 12 of these interventions belonging to four chemical classes are recommended by the WHO Pesticide Evaluation Scheme (WHOPES) for IRS37. Current strategies for controlling malaria vectors mainly include IRS with synthetic DDT/pyrethroids and durable LLINs14. WHO recommends that these insecticides' susceptibility status needs to be monitored annually13. However, the last two decades have seen the use of insecticides everywhere, especially pyrethroids, causing widespread resistance and compromising the effectiveness of vector control38. Besides, when this situation is detected, the intensity, biochemical and molecular mechanisms should also be investigated. The accurate information about the underlying resistance mechanism and its intensity or frequency in the malaria vector turn to update the vector control program and ensure the timely management of insecticide resistance23. Therefore, biochemical and molecular tests are recommended to understand the mechanism of pyrethroid resistance, and there have been several reports about this situation in the malaria vectors. However, several control strategies are used to fight resistance, such as rotation, mixture, using biological control, and integrated vector management27.
This study had limitations, such as the dissimilar variables investigated, which produced an incomplete analysis. There were only 15 articles from eight countries that correlated with the inclusion criteria from the selected ten years of studies. The data on each country's mortality rate presented only the smallest value, therefore, making it difficult to explore the whole data that need to make the discussion complete. In some countries, the bioassay test did not use carbamate, even though it was effective for controlling certain types of Anopheles.
The reports of pyrethroid resistance were quite focused on because it is considered effective in the malaria vector control. Several strategies are needed, including management plans in selecting insecticides, using a rotation system during the field interventions, regular monitoring, and integrating vector control based on physics, chemistry, and biology. All these need to be supported by cross-sector policies and cooperation to achieve the 2030 malaria-free target.
All data underlying the results are available as part of the article and no additional source data are required.
Figshare: PRISMA 2009 checklist for an article entitled Current status of insecticide resistance in malaria vectors in the Asian countries: systematic review. https://doi.org/10.6084/m9.figshare.1358607815.
This project contains the following extended data:
Figshare: PRISMA checklist for ‘Current status of insecticide resistance in malaria vectors in the Asian countries: systematic review’. https://doi.org/10.6084/m9.figshare.1358251712.
Data are available under the terms of the Creative Commons Attribution 4.0 International license (CC-BY 4.0).
DS contributed in designing and conducting the study, and also writing the draft of the manuscript, while DP searched and extracted the used data from the databases. The authors analyzed, edited, read, and approved the final manuscript in the English language. DS: Funding Acquisition of the financial support for the project leading to this publication.
The authors are grateful to the Directorate of Research and Community Engagement for giving the Indexed International Publication for Project grant and financial support. Authors also would like to thank MS. Rusyda Ihwani Tantia NOVA, SKM, M.Kes for her comments for improving this work.
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Are the rationale for, and objectives of, the Systematic Review clearly stated?
Yes
Are sufficient details of the methods and analysis provided to allow replication by others?
Yes
Is the statistical analysis and its interpretation appropriate?
Not applicable
Are the conclusions drawn adequately supported by the results presented in the review?
Partly
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Medical Entomology
Are the rationale for, and objectives of, the Systematic Review clearly stated?
Yes
Are sufficient details of the methods and analysis provided to allow replication by others?
Yes
Is the statistical analysis and its interpretation appropriate?
Not applicable
Are the conclusions drawn adequately supported by the results presented in the review?
Partly
Competing Interests: No competing interests were disclosed.
Reviewer Expertise: Medical entomology
Alongside their report, reviewers assign a status to the article:
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Version 1 10 Mar 21 |
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Provide sufficient details of any financial or non-financial competing interests to enable users to assess whether your comments might lead a reasonable person to question your impartiality. Consider the following examples, but note that this is not an exhaustive list:
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