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Systematic Review

Current status of insecticide resistance in malaria vectors in the Asian countries: a systematic review

[version 1; peer review: 2 approved with reservations]
PUBLISHED 10 Mar 2021
Author details Author details
OPEN PEER REVIEW
REVIEWER STATUS

Abstract

Background: The application of insecticides for malaria vector control has remained a global problem, due to the current trend of increased resistance against these chemicals. This study aims to determine the insecticide-resistant status in Asia and how to implement the necessary interventions. Moreover, the implications of resistance in malaria vector control in this region were studied.
Methods: This systematic review was conducted using a predefined protocol based on PRISMA-retrieved articles from four science databases, namely ProQuest, Science Direct, EBSCO, and PubMed in the last ten years (2009 to 2019). The searching process utilized four main combinations of the following keywords: malaria, vector control, insecticide, and Asia. In ProQuest, malaria control, as well as an insecticide, were used as keywords. The following criteria were included in the filter, namely full text, the source of each article, scholarly journal, Asia, and publication date as in the last ten years.
Results: There were 1408 articles retrieved during the initial search (ProQuest=722, Science Direct=267, EBSCO=50, PubMed=285, and Scopus=84). During the screening, 27 articles were excluded because of duplication, 1361 based on title and abstract incompatibility with the inclusion criteria, and 20 due to content differences. In the final screening process, 15 articles were chosen to be analyzed. From the 15 articles, it is known that there was dichlorodiphenyltrichloroethane (DDT) and pyrethroids resistance in several anopheles species with a mortality rate of less than 80%.
Conclusions: The report on the pyrethroid resistance was complicated, since this insecticide was considered effective in malaria vector control. Therefore, several strategies were required, including the management plans in selecting insecticides, using a rotation system during interventions in the field, regular monitoring, and integrating vector control based on physics, chemistry, and biology. All of these need to be supported by cross-sector policies and cooperation in achieving the 2030 malaria-free target.

Keywords

Anopheles; Malaria Elimination; Vector Control Program; Insecticide Resistance; Asian Countries

Introduction

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.

Methods

Search strategy

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.

Inclusion and exclusion criteria

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.

Study selection

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.

Data extraction and analysis

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.

Results

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.

d57d6a20-6c7c-4b37-9586-e911530ef3e9_figure1.gif

Figure 1. PRISMA flow diagram of systematic review inclusion and exclusion process.

The 15 eligible articles originated from eight Asian countries published from 2012 to 2019 journals are shown in Table 1.

Table 1. Article characteristics.

AuthorsTitlePublishCountryStudy periodsPublisherReference
Ahmad et al.Status of insecticide resistance in high-risk malaria
provinces in Afghanistan.
2016AfghanistanAugust to October 2014Malaria Journal24
Mishra et al.Insecticide resistance status of Anopheles culicifacies in
Madhya Pradesh, central India
2012IndiaAugust to September 2009Journal 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
2014IndiaJune–August 2011Journal of Vector-
Borne Diseases
21
Sahu et al.Triple insecticide resistance of Anopheles culicifacies: A
practical impediment for malaria control in Odisha State,
India.
2015IndiaApril to June 2014Indian Journal of
Medical Research
19
Chand et al.Insecticide resistance status of An. culicifacies in Gadchiroli
(Maharashtra) India
2017IndiaAugust 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
2013Thailand2000–2010Parasites & Vectors 26
Chaumeau et al.Insecticide resistance of malaria vectors along the
Thailand-Myanmar border
2017ThailandAugust and November 2014,
July 2015
Parasites & Vectors 20
Sumarnrote et al.Insecticide resistance status of Anopheles mosquitoes in
Ubon Ratchathani province, Northeastern Thailand
2017Thailand 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
2018IranApril–June 2015Journal of
Arthropod-Borne
Diseases
22
Vatandoost et al.Indication of pyrethroid resistance in the main malaria
vector, Anopheles stephensi from Iran
2012IranSpring 2011Asian Pacific Journal
of Tropical Medicine
27
Marcombe et al.Insecticide resistance status of malaria vectors in Lao PDR2017LaoThe 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
2014ChinaJuly–August 2012Parasites & Vectors 29
Dai et al.Development of insecticide resistance of malaria vector
Anopheles sinensis in Shandong Province In China
2015China2003–2012Malaria 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
2012Sri 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
2019TurkeyApril 2014 and September 2015ActaTropica 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.

Table 2. Sample and location characteristics.

Study locationCountryAnopheles
species
Sample
adult female
mosquitos
(n)
Vector habitatReference
Nangarhar, Laghman, Kunar, Ghazni, and
Badakhshan
AfghanistanAn. stephensi,
An. superpictus,
An. culicifacies
2049Ricefield, river
stream, ponds, and
water puddle
24
Madhya Pradesh IndiaAn. culicifaciesNAForest8
Asom-Meghalaya border area, northeast India IndiaAn. annularis200Forest, ponds
irrigation
21
Rayagada, Nowrangpur, Kalahandi, Malkangiri
and Koraput
IndiaAn. culicifacies1740Forest19
Gadchiroli district IndiaAn. culicifaciesNAForest 25
Chiang Mai-Chiang Dao, Mae Hongsom, Phrae ThailandAn. minimus
An. annularis
NAPaddy fields and
rivulet
26
Thailand-Myanmar Border ThailandAn. annularis,
An. minimus,
An. hyrcanus,
An. barbirostris,
An. vagus,
An. maculatus,
An. jamessi,
An. scanloni,
An. kochi,
An. tesselatus
5896Agriculture20
Khong Chiam, Sirindhorn, Buntharik, and
Nachaluay
ThailandAn. hyrcanus,
An. barbirostris,
An. maculatus,
An. nivipes,
An. philipinensis,
An. vagus
An. dirus
An. karwari
2088Forest and ricefield17
Chabahar Seaport, southeast corner of Iran IranAn. stephensi317Seaport22
Sistan and BaluchistanIranAn.stephensi733Coastal 27
Phongsaly, Bokeo, LuangPrabang, Vientiane
Pro, Borlikhamxay, Khammouane, Savannakhet,
Saravane, Sekong, Attapeu.
LaoAn. minimus,
An. hyrcanus,
An. vagus
An. maculatus
An. nivipes
An. philipinesnis
An. umbrosus
An. kochi
An. tesselatus
An. aconitus
3977Forest, village,
agriculture
28
Hainan Island ChinaAn. sinensis,
An. vagus
1468Mountainous and
ricefield
29
Shandong ProvinceChina An. sinensis4370Irrigated ricefield,
aquatic habitat, and
small ponds
30
Batticaloa, Puttalam, Trincomalee and Ampara Sri LankaAn. subpictus
An. sundaicus
256Coastal and inland31
Southeastern Anatolia and the Mediterranean TurkeyAn. superpictus,
An. sacharovi
1230Agricultural, 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).

Table 3. WHO bioassay method.

CountryWHO bioassay with insecticides
OrganochlorineOrganophosphateCarbamatePyrethroid
DDT (%)malathion (%)Bendiocarb
(%)
Propoxur
(%)
Permethrin
(%)
Deltamethrin
(%)
Lambda-
cyhalothrin (%)
Cyfluthrin
(%)
Etofenprox
(%)
Afghanistan4.05.00.1NA0.750.05NANANA
India4.05.0NANANA0.05NANANA
India4.0NANANANA0.05NANANA
India4.05.0NANANA0.05NANANA
India4.0NANANA0.750.050.050.15NA
Thailand4.0NANANANANANANANA
Thailand4.0NANANA0.750.05NANANA
Thailand4.0NANANA0.750.05NANANA
Iran4.0NANANA0.750.050.050.150.5
Iran4.0NANANA0.750.050.050.150.5
Lao4.0NANANA0.750.05NANANA
China4.05.0NANANA0.05NANANA
China4.05.0NANANA0.05NA0.15NA
Sri Lanka4.05.0NANANA0.050.05NANA
Turkey4.05.0NA0,10,750,05NANA0.5

WHO=world health organization. DDT=dichlorodiphenyltrichloroethane. NA= not available.

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.

Table 4. Mortality rate of insecticide resistance bioassay in Anopheles.

NoAnopheles
species
Percentage of mortality (Susceptibility Status)Reference
OrganochlorineOrganophosphateCarbamatePyrethroid
DDT (%)Malathion (%)Bendiocarb
(%)
Propoxur
(%)
Permethrin
(%)
Deltamethrin
(%)
Lambda-
cyhalothrin
(%)
Cyfluthrin
(%)
Etofenprox
(%)
1An. stephensi*31-60 (R)47-97 (R)87-100 (PR)NA87-91 (PR)66-78 (R)24
45 (R)NANANA92.3 (PR)96(PR)88.4 (PR)55 (R)91 (PR)27
62 (R)NANANANA96 (PR)89 (PR)82 (PR)100 (S)22
2An. superpictus*50-86.7 (R-PR)61.7-88.3 (R-PR)68.3-91.7
(R-PR)
NANANANANA32
100 (S)100 (S)92 (PR)NA100 (S)85 (PR)NANANA24
3An. culicifacies*6.6-26.6 (R)65.4-100 (R-S)NANANA71.6-94.1 (R-PR)NANANA8
11.4-15.3 (R)60.4-76.2 (R)NANANA72.6-84 (R-PR)NANANA19
37.1 (R)74 (R)NANA91.3 (PR)83.8 (PR)59.9 (R)70.2 (R)NA25
81 (PR)95 (PR)100 (S)89 (PR)64(R)24
4An. annularis11.9-28.3 (R)NANANANA97.7-98.1(PR-S)NANANA21
NANANANANANANANANA26
100 (S)20
5An. minimus*NANANANANANANANANA26
NANANANANA92 (PR)NANANA20
98-100 (S)NANANA100 (S)100 (S)NANANA28
6An. hyrcanus*57 (R)NANANA48 (R)33 (R)NANANA20
72-83 (R-PR)NANANA65-87 (R-PR)45-85 (R-PR)NANANA17
90 (PR)NANANANANANANANA28
7An. barbirostris*69 (R)NANANANA97-100 (PR-S)NANANA17
74 (R)NANANA84 (PR)72 (R)NANANA20
8An. vagus*34-61 (R)NANANA89-95 (PR)79-95 (R-PR)NANANA28
67.1-88.8 (R-PR)77.3-88.9 (R-PR)NANANANANANANA29
97 (PR)NANANA95 (PR)75 (R)NANANA20
NANANANANA97.9-100 (S)NANANA29
NANANANANA100 (S)NANANA17
9An. maculatus*86-100 (PR-S)NANANANANANANANA28
NANANANA97 (PR)85 (PR)NANANA20
NANANANANA100 (PR)NANANA28
NANANANANA100 (PR)NANANA17
10An. jamessiNANANANANA87 (PR)NANANA20
11An. nivipes0-100 (R-S)NANANA90-100 (PR)100 (S)NANANA28
NANANANA100 (S)NANANANA17
12An. philippinenses33-100 (R-S)NANANA100 (S)NANANANA28
100 (S)NANANA100 (S)100 (S)NANANA17
13An. umbrosus63 (R)NANANA86 (PR)100 (S)NANANA28
14An. sinensis*30.4 (R)86.6 (PR)NANANA35.8 (R)NA32.4 (R)NA30
72.7-78.4 (R)NANANANA85.8-91(PR)NANANA29
15An. subpictus*16-35 (R)49-69 (R)NANANA82-96 (PR)72-97 (R-PR)NANA31
16An. sacharovi*55-78.3(R)58.3-90 (R-PR)NA68.3-90
(R-PR)
NANANANANA32
17An.scanloni84 (PR)NANANANANANANANA20
18An.kochi82-100 (PR-S)NANANA100 (S)100 (S)NANANA28
NANANANANA98 (S)NANANA20
19An.tessellatus14 (R)NANANA100 (S)NANANANA28
NANANANANA98 (S)NANANA20
20An.sundaicus38-47 (R)93-98 (PR-S)NANANA97-100 (S)100 (S)NANA31
21An.aconitus100 (S)NANANA100 (S)100 (S)NANANA28
22An.dirusNANANANA100 (S)NANANA17
23An.karwariNANANANA100 (S)NANANA17

*Main vector

DDT=dichlorodiphenyltrichloroethane. NA=not available, S=Susceptible (90-97% mortality suggest), P=Possible Resistance, R=Resistance= < 90%.

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.

Table 5. Insecticide resistance strategies.

CountryStudy locationLocation
characteristic
Insecticide resistance strategiesReference
AfganistanNangarhar, 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
IndiaMadhya PradeshForestResistance 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 districtForest
ThailandChiang Mai-Chiang Dao, Mae Hongsom,
Phrae
Paddy fields and rivuletVector 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 BorderAgriculture
Khong Chiam, Sirindhorn, Buntharik, and
Nachaluay
Forest and rice field
IranChabahar Seaport, southeast corner of IranSeaportBiological, 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 BaluchistanCoastal
LaoPhongsaly, Bokeo, LuangPrabang,
Vientiane Pro, Borlikhamxay, Khammouane,
Savannakhet, Saravane, Sekong, Attapeu.
Forest, villageRoutine 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
ChinaHainan IslandMountainous 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 ProvinceIrrigated ricefield,
aquatic habitat, and
small ponds
Sri LankaBatticaloa, Puttalam, Trincomalee and
Ampara
Coastal and inlandMonitoring 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
TurkeySoutheastern 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

Discussion

Study sites

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.

Type of insecticide

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.

Insecticide resistance level

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.

Mortality rate of the Anopheles

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.

Intervention

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.

Limitations

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.

Conclusion

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.

Data availability

Underlying data

All data underlying the results are available as part of the article and no additional source data are required.

Extended data

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:

  • - PRISMA flow diagram of systematic review inclusion and exclusion process

Reporting guidelines

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).

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Susanna D and Pratiwi D. Current status of insecticide resistance in malaria vectors in the Asian countries: a systematic review [version 1; peer review: 2 approved with reservations]. F1000Research 2021, 10:200 (https://doi.org/10.12688/f1000research.46883.1)
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ApprovedThe paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approvedFundamental flaws in the paper seriously undermine the findings and conclusions
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Reviewer Report 01 Oct 2021
Charles M. Mbogo, Kenya Medical Research Institute-Wellcome Trust Research Program, Nairobi, Kenya 
Approved with Reservations
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The authors are reporting on insecticide resistance data compiled through systematic review from Asian countries. The purpose of this systematic review was to understand the current status of insecticide resistance among malaria vectors and the implementation of the interventions.
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Mbogo CM. Reviewer Report For: Current status of insecticide resistance in malaria vectors in the Asian countries: a systematic review [version 1; peer review: 2 approved with reservations]. F1000Research 2021, 10:200 (https://doi.org/10.5256/f1000research.49960.r93580)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.
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Reviewer Report 30 Jun 2021
Josiane Etang, Organization for Coordination of the Fight Against Endemic Diseases in Central Africa (OCEAC), Yaoundé, Cameroon;  Faculty of Medicine and Pharmaceutical Sciences, University of Douala, Douala, Cameroon 
Approved with Reservations
VIEWS 22
The emergence and spread of Anopheles resistance to insecticides is a growing issue, that jeopardizes the effectiveness of currently available core malaria vector control tools, i.e. Long Lasting Insecticidal nets (LLINs) and Indoor Residual Spraying (IRS).

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Etang J. Reviewer Report For: Current status of insecticide resistance in malaria vectors in the Asian countries: a systematic review [version 1; peer review: 2 approved with reservations]. F1000Research 2021, 10:200 (https://doi.org/10.5256/f1000research.49960.r87116)
NOTE: it is important to ensure the information in square brackets after the title is included in all citations of this article.

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Approved - the paper is scientifically sound in its current form and only minor, if any, improvements are suggested
Approved with reservations - A number of small changes, sometimes more significant revisions are required to address specific details and improve the papers academic merit.
Not approved - fundamental flaws in the paper seriously undermine the findings and conclusions
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