Knockdown resistance (kdr)-associated organochlorine resistance in mosquito-borne diseases (Culex pipiens): A systematic study of reviews and meta-analysis

doi:10.21203/rs.3.rs-4023980/v1

Background

Culex pipiens is the vector of a large number of pathogens in humans. Use of insecticides to deal with this vector is the most important way to controlling it. However, in recent decades, resistance to insecticides has been reported in this vector. One of the main insecticides used to fight this vector is organochlorine insecticides. Accordingly, this study was conducted to investigate the prevalence of Knockdown resistance (kdr) in Culex pipiens against organochlorine insecticides.

Methods

This study was conducted via systematic review and meta-analysis approach in the field of kdr prevalence in Culex pipiens against organochlorine insecticides. Accordingly, during the search in the scientific databases PubMed, Web of Science, Biooan.org, Embase, ProQuest, Scopus, and Google Scholar without time limit until the end of November 2023, all related articles were extracted and analyzed. The statistical analysis of the data was performed using random and fixed effects model in the meta-analysis, Cochran's test, I² index, and meta-regression by STATA software version 17.

Results

seven studies with a sample size of 2,029 Culex pipiens were included in the meta-analysis process. Based on the findings, the kdr resistance prevalence against Deltamethrin, Malathion, Permethrin, and DDT insecticides was estimated as 30.6%, 42%, 17.9%, and 76.3% respectively. Among them, the highest resistance was observed to DDT and the lowest to Permethrin.

Conclusion

Based on the findings, a large proportion of Culex pipiens mosquitoes were resistant to DDT insecticide. However, this vector was highly sensitive to Deltamethrin, Malathion, and Permethrin insecticides. Given the different resistance ratios in different regions of the world, it is recommended to conduct studies on the prevalence of kdr in Culex pipiens.

Knockdown resistance

Organochlorine insecticide

Culex pipiens

Systematic study of reviews and meta-analysis

Culex is one of the most widespread mosquito species in the world (1). They opportunistically feed on humans and animals, which provides suitable conditions for the transmission of common diseases between humans and animals and is a serious threat to public health (2). Culex has adapted to human habitats over the years and is expanding in the urban environment due to the rapid and unplanned expansion of cities as well as the lack of suitable environmental conditions, the presence of stagnant water, drains, organically polluted places, and pits (3, 4). Culex pipiens is one of the most important groups of Culex, which includes six members of Cx. pallens Coquillet, Cx. Quinquefasciatus Say, Cx. australicus Dobrotworsky & Drummond, Cx. molestus Forskell, Cx. pipiens Linneaus and Cx. Globocoxitus is Dobrotworsky (5, 6). Culex pipiens is an important vector of a large number of pathogenic pathogens and parasites in the world. This mosquito is known as a vector of West Nile virus (WNV), Rift Valley fever virus (RVFV), Wuchereria bancrofti (Cobbald, the causative agent of filariasis), and Japanese and St. Louis encephalitis (7–9).

Diseases transmitted through vectors (mosquitoes) continue to affect the public health of humans. Due to the lack of vaccination to prevent vector-borne diseases, combating them is considered the best method of intervention. As a result, nowadays chemical insecticides are mainly used to control the vectors. Four groups of insecticides including organochlorines, organophosphates, carbamates, and pyrethroids are the main insecticides used to fighting vectors (10). Pyrethroids account for about 15% of the insecticides used to combat vectors in the world. Pyrethroids are widely used to control vectors due to their low toxicity to humans and high lethal effect on insects (11). Organochlorines have also been widely used since the distant past to fight against vectors. By acting on the central and peripheral nervous system of insects, these insecticides lead to paralysis and death of carriers through interaction with the voltage-gated sodium channel (VGSC) as well as increasing its sensitivity to depolarization by inhibiting inactivation processes (12, 13).

In response to the long-term, extensive, and incomplete use of these insecticides over time, it has led to the natural selection of insects and a reduction in the sensitivity of the target site to them, which is known as "KDR". It is caused by the insensitivity of the target site due to the mutation in the voltage-sensitive sodium channel gene (Vssc) (14). Resistance to DDT and deltamethrin is often associated with mutations in the sodium channel gene, which reduces neuronal sensitivity to these insecticides (15). In the studies conducted worldwide, kdr resistance was reported in Culex pipiens and it was shown that the ratio of resistance is different in different countries (16). Studies have mentioned that three groups of glutathione-S-trans-ferases (GST), esterase, and cytochrome P450 oxidases play a role in creating metabolic resistance to organochlorine, organophosphate, and pyrethroids in Culex pipiens (17). In the field of Kdr resistance in Culex pipiens, it has been reported that two mutations L1014F and L1014S cause Kdr resistance in it (18).

Identifying mutations related to resistance is essential for managing together with using appropriate and effective insecticides to control insects. Note that Culex pipiens is a carrier of some pathogenic pathogens for humans and is now spreading in the world (19, 20). Determining the level of sensitivity or resistance to insecticides is essential to dealing with this vector. Accordingly, the present study was conducted to investigate the prevalence of kdr resistance in Culex pipiens against organochlorine insecticides via a systematic review and meta-analysis.

This study was performed via systematic review and meta-analysis based on the guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) in the field of kdr prevalence in Culex pipiens against organochlorine insecticides (21). This research has been registered in the International Prospective Register of Systematic Review (PROSPERO) under the code CRD42021231605.

Search Strategy

The two researchers extract papers from scientific databases of PubMed, Web of Science, Biooan.org, Embase, ProQuest, Scopus, and Google Scholar using keywords Resistance, knockdown resistance, KDR, insecticide, Organochlorine insecticide, chlorinated insecticide, chlorophenyl, dichloroethane, DDT, parachlorophenyl, dichlorodiphenyldichloroethane, dieldrin, permethrin, deltamethrin, malathion, Culex and Culex pipiens. They then investigated the title, abstract and full text of the articles singularly and in combination using OR, AND and NOT operators without time limit until the end of November 2023.

Inclusion and Exclusion Criteria

Based on the PICO model, published English-language articles conducted on Culex pipiens as well as examining kdr resistance to organochlorine insecticides, and the prevalence of resistance or mortality in exposure to organochlorine insecticides as well as showing good quality were included in the study. The articles that were conducted on other insects, and other insecticides (except organochlorine insecticides), those not dealing with kdr resistance, lacking the desired quality, and in the review method, case report or Letters to the editor were excluded from the study.

Quality Assessment

The quality assessment of the articles was done based on 22 parts of the STROBE (Strengthening the Reporting of Observational Studies in Epidemiology) checklist, which investigated compliance with the principles of writing and implementation in the title, the method of reporting findings, limitations, and conclusions. Each part of this checklist is given a score based on its importance; the maximum possible score is 33. Based on the obtained score, the studies were divided into three levels low, medium, and high quality (22).

Data Extraction

Initially, the articles were investigated by two researchers independently by examining the title and abstract, taking into account the inclusion and exclusion criteria. Then, the full text of the articles was inspected by these researchers, and if the articles were rejected by two researchers, the reason was mentioned. Also, in case of disagreement between them, the article was refereed by a third researcher. Data extraction was performed using a pre-prepared checklist which included the first author's name, study place, study year, sample size, insecticide type, kdr resistance prevalence, and mortality.

Selection of Studies

A total of 14536 studies were extracted by searching the databases. At first, the articles were entered into the Endnote software, and after the initial review, 6528 articles were excluded from the study due to being duplicates. Next, by checking the titles and abstract of the articles, 7839 articles were removed as they were not relevant, and after reviewing the full text of the articles, 162 articles were removed due to lack of investigation of the prevalence of kdr resistance or resistance to organochlorine insecticide. Finally, 7 articles met the inclusion criteria and included in the meta-analysis process (Fig. 1).

Statistical Analysis

Statistical analysis of the data was done using random and fixed effects models in meta-analysis, plus I² index and Cochran's test. Further, funnel plot was used to investigate the publication bias and Meta regression to explore the relationship between the sample size and the prevalence of KDR. Data analysis was done using STATA software version 17.

Seven studies with a sample size of 2029 Culex pipiens mosquitoes that were conducted between 2006 and 2023 were included in the study. Two studies were conducted in China, two in Iran, and one study each in Morocco, Egypt, and America. The characteristics of the reviewed articles are presented in Table 1.

Table 1- characteristics of the articles included in the meta-analysis

Author	Year of study	Place of study	Sample size	Mortality rate (%)
Author	Year of study	Place of study	Sample size	Deltamethrin	DDT	Permethrin	Malathion
Tmimi FZ (33)	2018	Morocco	531	-	16.00	63.00	52.00
Zeidabadinezhad R (34)	2019	Iran	239	96.90	-	-	-
McAbee RD (8)	2023	USA	60	-	67.00	87.00	-
Xing W (35)	2018	China	364	68.57	11.20	-	53.78
Rahimi S (36)	2019	Iran	120	49.00	12.00	66.70	29.70
Liu H (37)	2019	China	595	39.04-98.96	-	-	-
Zayed ABB (38)	2006	Egypt	120	90.60	17.80	72.90	96.00

Based on the findings of the meta-analysis of the six studies conducted on the prevalence of kdr resistance in Culex pipiens against Deltamethrin insecticide, the ratio of sensitivity to Deltamethrin insecticide was estimated at 69.4%. showing 30.6% of Culex pipiens mosquitoes were resistant to Deltamethrin. In terms of heterogeneity between studies, the I² index was estimated at 98.41%, indicating existence of heterogeneity between studies (Fig. 2). The investigation of the prevalence of Culex pipiens resistance against Malathion insecticide revealed that the prevalence of sensitivity in Culex pipiens mosquitoes was 58.1%, demonstrating that about 42% of Culex pipiens have kdr resistance to Malathion (Fig. 3).

In the context of the prevalence of kdr resistance in Culex pipiens against Permethrin insecticide, the findings revealed that 72.1% of Culex pipiens were sensitive to Permethrin and it shows that 17.9% of them had kdr resistance (Fig. 4). The attenuation ratio against DDT insecticide was estimated at 23.7%, which shows that 76.3% of Culex pipiens have kdr resistance against DDT (Fig. 5).

The publication bias was examined using the funnel plot and Egger's test. Due to the symmetry of the funnel plot, it can be mentioned that publication bias did not occur, and the result of Egger's test was not significant in this regard (P = 0.14) (Fig. 6). Also, using meta-regression, the relationship between sample size and mortality ratio was investigated. According to the slope of the graph, the mortality ratio diminished with the increase of the sample size, showing the resistance ratio was higher in larger populations (Fig. 7).

This study was conducted on the prevalence of kdr resistance in Culex pipiens against Deltamethrin, Permethrin, Malathion, and DDT insecticides via meta-analysis method. Based on the findings, the kdr resistance ratio against Deltamethrin, Malathion, Permethrin, and DDT insecticides was estimated as 30.6%, 42%, 17.9%, and 76.3% respectively. Among them, the highest resistance was observed to DDT and the lowest to Permethrin. It can be mentioned that the most effective insecticide to deal with Culex pipiens is Permethrin and Deltamethrin. In studies of insecticide target sites in Culex pipiens, G119S ace-1 and L1014F kdr mutants. Regarding resistance to DDT, these mutations were identified and shown to play a role in creating resistance in Culex pipiens (23, 24). Studies have also shown that the L1014F kdr mutation is widely present in Culex pipiens. This mutation plays an important role in resistance to organochlorine and organophosphate insecticides (25). The mutation from leucine to serine (TTA to TCA) is another mutation identified in Culex pipiens resistance, which has been observed in different countries including China, America, and Japan (26–28). The L1014C mutation with the substitution of leucine (TTA) for cysteine (TGT) is another mutation identified in Culex pipiens (26). Mosquitoes with the Phe/kdr mutation also showed high resistance to pyrethroids and DDT, but the Ser/kdr mutation confers high resistance to DDT and low resistance to pyrethroids (29). The presence of various mutations in Culex pipiens indicates the presence of high resistance and their spread in different regions of the world. Because under selection pressure, carriers can acquire resistance and transfer it to the next generations, as a result, this phenomenon can lead to an increase in the prevalence of kdr resistance in Culex pipiens mosquitoes in the world. In a study conducted in northern Iran, the sensitivity ratio of Culex pipiens mosquitoes to DDT was low, but a large ratio of them was sensitive to deltamethrin (30). In another study by Salim-Abadi et al. (2016) in Iran, Culex pipiens were sensitive to Deltamethrin and resistant to DDT (31). In the study of Akiner et al. (2009) in Turkey, Culex pipiens was highly sensitive to Malathion, Deltamethrin, and Permethrin insecticides, but highly resistant to DDT (32).

In general, based on the findings of the present study, it can be mentioned that Culex pipiens is highly sensitive to Deltamethrin, Malathion, and Permethrin insecticides, but it has high KDR resistance to DDT insecticide. Accordingly, it is recommended to use effective insecticides to fight and control this vector. Also, due to the different resistance ratios in different regions of the world, it is recommended to conduct studies on the prevalence ratio of kdr resistance.

According to the findings, a large proportion of Culex pipiens mosquitoes were resistant to DDT insecticide. However, this vector was highly sensitive to Deltamethrin, Malathion, and Permethrin insecticides. Since few studies have been done in this field, it is recommended to conduct studies to evaluate the prevalence of resistance in countries where this vector is endemic.

Ethical considerations

Ethical approval for this study was obtained from the Shiraz University of Medical Sciences (Iran) Ethics Committee.

Conflict of interest

The authors declare no conflict of interest.

Funding

It was funded by the Vice-Chancellor for Research of Shiraz University of Medical Sciences.

Availability of data and materials

All obtained data are included in the text.

Authors' contributions

EA determined the title, wrote and registered the protocol, and submitted the article. EA, M.M and FM extracted the files from the databases. AT, MH, and EA, screening, and selection of final articles. AA and EA, data extraction. SD wrote the article. All authors read and approved the final manuscript.

Acknowledgments

The authors thank the Research Vice-Chancellor of Shiraz University of Medical Sciences.

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No competing interests reported.

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Knockdown resistance (kdr)-associated organochlorine resistance in mosquito-borne diseases (Culex pipiens): A systematic study of reviews and meta-analysis

Status:

Version 1

Abstract

Background

Methods

Results

Conclusion

Figures

Introduction

Materials and Methods

Search Strategy

Inclusion and Exclusion Criteria

Quality Assessment

Data Extraction

Selection of Studies

Statistical Analysis

Results

Discussion

Conclusion

Declarations

References

Additional Declarations

Supplementary Files

Status:

Version 1