Indication of pyrethroid resistance in the main malaria vector, Anopheles stephensi from Iran

A quantitative and systematic analysis of Anopheles stephensi bionomics and control approaches

Anopheles stephensi is a mosquito endemic to South Asia and the Arabian Peninsula that has recently been detected in eight African countries, posing a significant threat to global malaria control efforts. A challenge with An. stephensi is that it requires unique surveillance and control tools when compared to other malaria vectors. Through a systematic literature review, we investigated the efficacy of trapping methods and controls for An. stephensi mosquitoes, with a focus on studies of its behavior and biology. Data from 83 articles (native range: Afghanistan, India, Iran, Iraq, Pakistan, and Qatar; invasive range: Djibouti, Ethiopia, Sri Lanka, Saudi Arabia, and Sudan) met our study inclusion criteria. Data from these studies revealed that using host-seeking animal baited traps increased the number of mosquitoes collected per trap per day in the native range when compared to host-seeking human baited traps. However, these differences were not present in data collection rate assessments from the invasive range. We also found that An. stephensi equally used a large variety of breeding habitats in the native range, but that it tended to prefer water reservoirs and wastewater in the invasive range. Finally, we found that temephos, fenthion, Bacillus thuringiensis israelensis, and Beauveri bassiana were more effective at reducing larvae in their native range compared to the approaches found in our systematic literature search, but the relative effectiveness of these approaches in the invasive range was less clear. Understanding proven historical surveillance and control approaches is essential to the advancement of invasive An. stephensi mitigation efforts, but continued investigations in the invasive range are critical to reducing the impacts of malaria morbidity and mortality.

Possible potential spread of Anopheles stephensi, the Asian malaria vector

BACKGROUND

Anopheles stephensi is native to Southeast Asia and the Arabian Peninsula and has emerged as an effective and invasive malaria vector. Since invasion was reported in Djibouti in 2012, the global invasion range of An. stephensi has been expanding, and its high adaptability to the environment and the ongoing development of drug resistance have created new challenges for malaria control. Climate change is an important factor affecting the distribution and transfer of species, and understanding the distribution of An. stephensi is an important part of malaria control measures, including vector control.

METHODS

In this study, we collected existing distribution data for An. stephensi, and based on the SSP1-2.6 future climate data, we used the Biomod2 package in R Studio through the use of multiple different model methods such as maximum entropy models (MAXENT) and random forest (RF) in this study to map the predicted global An. stephensi climatically suitable areas.

RESULTS

According to the predictions of this study, some areas where there are no current records of An. stephensi, showed significant areas of climatically suitable for An. stephensi. In addition, the global climatically suitability areas for An. stephensi are expanding with global climate change, with some areas changing from unsuitable to suitable, suggesting a greater risk of invasion of An. stephensi in these areas, with the attendant possibility of a resurgence of malaria, as has been the case in Djibouti.

CONCLUSIONS

This study provides evidence for the possible invasion and expansion of An. stephensi and serves as a reference for the optimization of targeted monitoring and control strategies for this malaria vector in potential invasion risk areas.

Evaluation of the knockdown resistance locus (kdr) in Anopheles stephensi (Diptera: Culicidae) in southeastern Iran

Background & objectives

The resistance to insecticide among Anopheles stephensi population due to insecticide selection pressure has been previously reported from Iran. The current study was performed to evaluate the susceptibility of different insecticide reagents against An. stephensi by bioassay and molecular methods in Saravan County, a malaria-endemic area in southeastern Iran.

Methods

An. stephensi mosquitoes were collected from different larval habitats in Saravan City, southeastern Iran in 2022. At first, the susceptibility of collected samples for DDT, permethrin, and deltamethrin were evaluated by bioassay test. The collected mosquitoes were then evaluated for the presence of different kdr mutations.

Results

Insecticide susceptibility tests were conducted on the field population of An. stephensi from Saravan, revealing its potential resistance to pyrethroids and DDT. Of the 150 An. stephensi samples, 4 % carried the kdr L1014F mutation as heterozygous and the rest of them were homozygous L1014 wild type.

Interpretation & conclusion

The current study revealed the presence of L1014F mutation for the first time in Iran. So, further monitoring of kdr mutations in the VGSC gene and resistance phenotypes should be performed.

Current Situation of Malaria and Resistance of Main Vectors to WHO Recommended Insecticides in an Endemic Area, Southeastern Iran

Although malaria is endemic in some areas of southeastern Iran, following the successful national malaria elimination plan, the local transmission area has been shrunk. The main cases in Iran are due to Plasmodium vivax followed by P. falciparum. This study was aimed to determine the current situation of malaria in Kerman Province of Iran and evaluate the insecticide resistance of main vectors. The field study was conducted in 2019. Data of new malaria cases were obtained from the health centers for the period of 2009-2018. Susceptibility status of Anopheles stephensi and An. dthali was evaluated against dichlorodiphenyltrichloroethane, Dieldrin, Malathion, Bendiocarb, Deltamethrin, and Temephos at the diagnostic dose. A total of 522 malaria cases were recorded and divided into indigenous (33.14%) and imported (66.86%) categories. The highest incidence of the disease was reported from the southern areas of the province, where all indigenous cases occurred. Adults of An. stephensi were resistant to dichlorodiphenyltrichloroethane while its resistance to be confirmed to dieldrin, bendiocarb and deltamethrin. As An. dthali had less than 98% mortality against bendiocarb, the resistance status should be confirmed with more tests. Our findings showed both species had less than 98% mortality against bendiocarb and deltamethrin insecticides which are used in malaria vector control program in Iran. Due to the susceptibility of these vectors to temephos, larviciding can be advised for vector control in this area.

Insecticidal Efficacy of Metarhizium anisopliae Derived Chemical Constituents against Disease-Vector Mosquitoes

Insecticides can cause significant harm to both terrestrial and aquatic environments. The new insecticides derived from microbial sources are a good option with no environmental consequences. Metarhizium anisopliae (mycelia) ethyl acetate extracts were tested on larvae, pupae, and adult of Anopheles stephensi (Liston, 1901), Aedes aegypti (Meigen, 1818), and Culex quinquefasciatus (Say, 1823), as well as non-target species Eudrilus eugeniae (Kinberg, 1867) and Artemia nauplii (Linnaeus, 1758) at 24 h post treatment under laboratory condition. In bioassays, Metarhizium anisopliae extracts had remarkable toxicity on all mosquito species with LC50 values, 29.631 in Ae. aegypti, 32.578 in An. stephensi and 48.003 in Cx. quinquefasciatus disease-causing mosquitoes, in A. nauplii shows (5.33-18.33 %) mortality were produced by the M. anisopliae derived crude extract. The LC50 and LC90 values were, 620.481; 6893.990 μg/mL. No behavioral changes were observed. A low lethal effect was observed in E. eugeniae treated with the fungi metabolites shows a 14.0 % mortality. The earthworm E. eugeniae mid-gut histology revealed that M. anisopliae extracts had no more harmful effects on the epidermis, circular muscle, setae, mitochondrion, and intestinal lumen tissues than chemical pesticides. By Liquid chromatography mass spectrometry (LC-MS) analysis, camphor (25.4 %), caprolactam (20.68 %), and monobutyl phthalate (19.0 %) were identified as significant components of M. anisopliae metabolites. Fourier transform infrared (FT-IR) spectral investigations revealed the presence of carboxylic acid, amides, and phenol groups, all of which could be involved in mosquito toxicity. The M. anisopliae derived chemical constituents are effective on targeted pests, pollution-free, target-specific, and are an alternative chemical insecticide.

Situation of insecticide resistance in malaria vectors in the World Health Organization of Eastern Mediterranean region 1990-2020

Malaria is the most important mosquito-borne disease, which is transmitted by Anopheles species. According to the recent report of World Health Organization, there were an estimated 229 million malaria cases in 2019 in 87 malaria endemic countries. There are several vector control method specially using pesticides. The aim of this study was to collect all the data about insecticide resistant of malaria vectors in the Eastern Mediterranean region countries. In this study, all the published papers related to insecticide resistance of malaria vectors in the region were collected and resistant status of vectors in the countries was mapped. Resistance to different insecticide classes such as pyrethroids, organophosphate, organochlorine and carbamates were evaluated using World Health Organization guidelines. Results showed a wide variety of susceptibility/resistance status to these chemicals according to the location, historical context of pesticide used, genetic background of vectors, age and abdominal conditions of adults may play a role in the susceptibility status of these species to different insecticides. The results of this study is providing a guideline for countries to manage their vector control activities against insecticide resistance of malaria vectors and provide novel approaches such as male sterility, using Wolbachia, using new insecticide with new mode of action.

Bioefficacy of bendiocarb WP80 in vector-borne and zoonotic diseases areas in borderline of Iran and Pakistan

Malaria and leishmaniasis are the public health problems in southern Iran. The main activity of vector control is indoor residual spraying using pyrethroids, using different insecticides as larviciding and impregnated bednets. The aim of study was to evaluate the biological assays of bendiocarb wettable powder (WP) at different surfaces of wall. The residual effect of bendiocarb WP80 at 400 milligram/meter square (mg/m²) was evaluated on various local surfaces of rooms such as mud and plaster as well as thatch roofs and wooden. World Health Organization standard cones using contact bioassays were carried out using laboratory reared sugar-fed, 48-72 h old females of Anopheles stephensi. Contact bioassays were carried out on sprayed surfaces for 150 days. Contact bioassay on surfaces treated with bendiocarb WP80 at different surfaces was estimated about 2 months. Fumigant tests of bendiocarb WP80 at 400 mg/m² revealed 50-93.83% mortality with 1 month persistency. The results showed that carbamate insecticide could be used as rotation with pyrethroids for malaria vector control. Monitoring and evaluation of environmental toxicology of pesticides is important for decision making for choosing appropriate pesticides for disease vector control.

Spatial Modelling of Malaria in South of Iran in Line with the Implementation of the Malaria Elimination Program: A Bayesian Poisson-Gamma Random Field Model

Background:

Malaria is the third most important infectious disease in the world. WHO propose programs for controlling and elimination of the disease. Malaria elimination program has begun in first phase in Iran from 2010. Climate factors play an important role in transmission and occurrence of malaria infection. The main goal is to investigate the spatial distribution of incidence of malaria during April 2011 to March 2018 in Hormozgan Province and its association with climate covariates.

Methods:

The data included 882 confirmed cases gathered from CDC in Hormozgan University of Medical Sciences. A Poisson-Gamma Random field model with Bayesian approach was used for modeling the data and produces the smoothed standardized incidence rate (SIR).

Results:

The SIR for malaria ranged from 0 (Abu Musa and Haji Abad districts) to 280.57 (Bandar–e-Jask). Based on model, temperature (RR= 2.29; 95% credible interval: (1.92–2.78)) and humidity (RR= 1.04; 95% credible interval: (1.03–1.06)) had positive effect on malaria incidence, but rainfall (RR= 0.92; 95% credible interval: (0.90–0.95)) had negative impact. Also, smoothed map represent hot spots in the east of the province and in Qeshm Island.

Conclusion:

Based on the analysis of the study results, it was found that the ecological conditions of the region (temperature, humidity and rainfall) and population displacement play an important role in the incidence of malaria. Therefore, the malaria surveillance system should continue to be active in the region, focusing on high-risk areas of malaria.

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

Background: The application of insecticides for malaria vector control has led to a global problem, which is the current trend of increased resistance against these chemicals. This study aimed to review the insecticide resistance status was previously determined 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 organochlorine (DDT), organophosphate (malathion), and pyrethroids resistance in several Anopheles species with a less than 80% mortality rate. Conclusion: This review found multiple resistance in several Anopheles includes resistance to pyrethroid. The reports of pyrethroid resistance were quite challenging because it is considered effective in the malaria vector control. Several countries in Asia are implementing an insecticide resistance management (IRM) strategy against malaria vectors following the Global Plan for IRM.

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

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.

Monitoring and Mapping of Insecticide Resistance in Medically Important Mosquitoes (Diptera: Culicidae) in Iran (2000-2020): A Review

BACKGROUND

Mosquitos due to their role in the transmission of different pathogens to humans are considered as an important group in the phylum Arthropoda. According to the WHO and FAO guideline different groups of insecticide applied for controlling pests in both the agricultural and public health sectors.

METHODS

All the data published about resistant status of the mosquitoes Anopheles, Culex, Aedes and Culiseta species were searched on PubMed, Elsevier, Web of Science, Magiran and google scholar. The objectives of this study was to review the trend of resistance to insecticides during 2000-2020 in medically important mosquitoes in Iran. The criteria for resistant are followed according to WHO guideline.

RESULTS

The Results showed that there are widespread, multiple resistances in the country to different organochlorine, organophosphates, carbamate and pyrethroids insecticides in the mosquitoes.

CONCLUSION

The effect of pesticide residues on the environment could be a cause for selection pressure on mosquitos and lead to insecticides resistance to them. Insecticides resistance is main challenge of the vector control program. Also result will provide a guideline for control of the mosquito-borne diseases in the country as well as the world.

Hidden genomic features of an invasive malaria vector, Anopheles stephensi, revealed by a chromosome-level genome assembly

BACKGROUND

The mosquito Anopheles stephensi is a vector of urban malaria in Asia that recently invaded Africa. Studying the genetic basis of vectorial capacity and engineering genetic interventions are both impeded by limitations of a vector's genome assembly. The existing assemblies of An. stephensi are draft-quality and contain thousands of sequence gaps, potentially missing genetic elements important for its biology and evolution.

RESULTS

To access previously intractable genomic regions, we generated a reference-grade genome assembly and full transcript annotations that achieve a new standard for reference genomes of disease vectors. Here, we report novel species-specific transposable element (TE) families and insertions in functional genetic elements, demonstrating the widespread role of TEs in genome evolution and phenotypic variation. We discovered 29 previously hidden members of insecticide resistance genes, uncovering new candidate genetic elements for the widespread insecticide resistance observed in An. stephensi. We identified 2.4 Mb of the Y chromosome and seven new male-linked gene candidates, representing the most extensive coverage of the Y chromosome in any mosquito. By tracking full-length mRNA for > 15 days following blood feeding, we discover distinct roles of previously uncharacterized genes in blood metabolism and female reproduction. The Y-linked heterochromatin landscape reveals extensive accumulation of long-terminal repeat retrotransposons throughout the evolution and degeneration of this chromosome. Finally, we identify a novel Y-linked putative transcription factor that is expressed constitutively throughout male development and adulthood, suggesting an important role.

CONCLUSION

Collectively, these results and resources underscore the significance of previously hidden genomic elements in the biology of malaria mosquitoes and will accelerate the development of genetic control strategies of malaria transmission.

Vector-borne diseases in Iran: epidemiology and key challenges

Vector-borne diseases have become a global health concern in recent decades as a result of global warming, globalization, growth in international trade and travel, use of insecticide and drug resistance. This review study addressed the key vector-borne diseases and their current status in Iran to emphasize the requirements for further research on vector-borne diseases. The dispersion patterns of these diseases differ in various regions. Some of them such as Crimean-Congo hemorrhagic fever, and Q fever are distributed all across Iran, whereas some others such as plague, leishmaniasis, tularemia, and malaria are restricted to specific areas. The high prevalence of vectors throughout the country necessitates enhancing the monitoring and surveillance of emerging and reemerging vector-borne diseases and their potential vectors.

Ecology of Malaria Vectors in an Endemic Area, Southeast of Iran

Background:

Malaria has long been regarded as one of the most important public health issues in Iran. Although the country is now in the elimination phase, some endemic foci of malaria are still present in the southeastern areas of the country. In some endemic foci, there are no data on the malaria vectors. To fill this gap, the present study was designed to provide basic entomological data on malaria vectors in the southeastern areas of Iran.

Methods:

Adult and larval stages of Anopheles mosquitoes were collected by using different catch methods. Resistance of the main malaria vector in the study area to selected insecticides was evaluated using diagnostic doses advised by the World Health Organization in 2013–2014.

Results:

A total of 3288 larvae and 1055 adult Anopheles mosquitoes were collected, and identified as: Anopheles stephensi (32.1%), Anopheles culicifacies s.l. (23.4%), Anopheles dthali (23.2%), Anopheles superpictus s.l. (12.7%), and Anopheles fluviatilis s.l. (8.6%). Anopheles stephensi was the most predominant mosquito species collected indoors at the study area, with two peaks of activity in May and November. This species was found to be resistant to DDT 4%, tolerant to malathion 5% and susceptible to other tested insecticides.

Conclusion:

All the five malaria vectors endemic to the south of Iran were collected and identified in the study area. Our findings on the ecology and resting/feeding habitats of these malaria vectors provide information useful for planning vector control program in this malarious area.

Evolution of insecticide resistance and its mechanisms in Anopheles stephensi in the WHO Eastern Mediterranean Region

BACKGROUND

While Iran is on the path to eliminating malaria, the disease with 4.9 million estimated cases and 9300 estimated deaths in 2018 remains a serious health problem in the World Health Organization (WHO) Eastern Mediterranean Region. Anopheles stephensi is the main malaria vector in Iran and its range extends from Iraq to western China. Recently, the vector invaded new territories in Sri Lanka and countries in the Horn of Africa. Insecticide resistance in An. stephensi is a potential issue in controlling the spread of this vector.

METHODS

Data were collated from national and international databases, including PubMed, Google Scholar, Scopus, ScienceDirect, SID, and IranMedex using appropriate search terms.

RESULTS

Indoor residual spaying (IRS) with DDT was piloted in Iran in 1945 and subsequently used in the malaria eradication programme. Resistance to DDT in An. stephensi was detected in Iran, Iraq, Pakistan, and Saudi Arabia in the late 1960s. Malathion was used for malaria control in Iran in 1967, then propoxur in 1978, followed by pirimiphos-methyl from 1992 to 1994. The pyrethroid insecticide lambda-cyhalothrin was used from 1994 to 2003 followed by deltamethrin IRS and long-lasting insecticidal nets (LLINs). Some of these insecticides with the same sequence were used in other malaria-endemic countries of the region. Pyrethroid resistance was detected in An. stephensi in Afghanistan in 2010, in 2011 in India and in 2012 in Iran. The newly invaded population of An. stephensi in Ethiopia was resistant to insecticides of all four major insecticide classes. Different mechanisms of insecticide resistance, including metabolic and insecticide target site insensitivity, have been developed in An. stephensi. Resistance to DDT was initially glutathione S-transferase based. Target site knockdown resistance was later selected by pyrethroids. Esterases and altered acetylcholinesterase are the underlying cause of organophosphate resistance and cytochrome p450s were involved in pyrethroid metabolic resistance.

CONCLUSIONS

Anopheles stephensi is a major malaria vector in Iran and many countries in the region and beyond. The species is leading in terms of development of insecticide resistance as well as developing a variety of resistance mechanisms. Knowledge of the evolution of insecticide resistance and their underlying mechanisms, in particular, are important to Iran, considering the final steps the country is taking towards malaria elimination, but also to other countries in the region for their battle against malaria. This systematic review may also be of value to countries and territories newly invaded by this species, especially in the Horn of Africa, where the malaria situation is already dire.

Evaluation of Susceptibility of Aedes caspius (Diptera: Culicidae) to Insecticides in a Potent Arboviral-Prone Area, Southern Iran

Background:

Southern part of the country is a high risk for mosquito transmitted Arboviruses. This study was carried out to determine the base line susceptibility of the Aedini mosquitoes to the WHO-recommended insecticide.

Methods:

Larval collection was carried out by dipping method and adult collection occurred by suction tube from January to December 2017. The adult susceptibility test was assessed to Bendiocarb 0.1%, DDT 4%, Deltamethrin 0.05%, Lambda-cyhalothrin 0.05%, Malathion 5% and, Permethrin 0.75% at different interval times as well as at discriminative dose recommended by WHO. The larval susceptibility test was occurred using Temephos and Bacillus thuringiensis serotype H-14, at different concentrations. The LT₅₀, LT₉₀ and LC₅₀, LC₉₀ values were calculated for plotting the regression line using Microsoft office Excel software ver. 2007.

Results:

Aedes caspius was quite resistant to DDT, Malathion, Bendiocarb and showed susceptible or tolerant to other insecticides.The LT₅₀ and LT₉₀ values to DDT in this species were 157.896, and 301.006 minutes, respectively. The LC₅₀ and LC₉₀ values of Ae. caspius to Temephos were 0.000068, and 0.000130ppm, the figures for B. thuringiensis was 111.62 and 210.2ppm, respectively.

Conclusion:

A routine and continuous study for monitoring and evaluation of different species of Aedes to insectides is recommend at different parts of country for decision making.

Autogeny in Culiseta longiareolata (Culicidae: Diptera) mosquitoes in laboratory conditions in Iran

Objectives

Culiseta longiareolata is a cosmopolitan species and has implicated in the transmission of avian malaria, tularemia, and arboviruses. Despite the wide distribution of Cs. longiareolata in Iran, little is known about its biology and physiology. The current research was conducted to study the autogeny behavior in this potential vector. During 2018, larvae and pupae were collected from Nazloo region in Urmia City using standard methods. Mosquitoes were reared in cages and fed by 5% sugar in laboratory conditions and were then dissected in phosphate-buffered saline (PBS) under a stereo microscope.

Results

In total, 230 adult female Cs. longiareolata mosquitoes were dissected. Egg rafts were observed in the ovary of only 10.86% unfed female mosquitoes. Autogeny behavior is a significant factor in the growth of population without a blood feeding. Therefore, it is necessary to study how autogenous reproduction affects mosquito-borne diseases.

Malaria situation in Iran: 2002-2017

Background

Malaria is considered as a major threat to health systems. It is still considered as one of the most important infectious diseases in Iran, but with an elimination goal in 2025. This study aimed to review the malaria situation in Iran over the 16 years.

Methods

The data was collected from epidemiological registration forms that had been completed by physicians and malaria focal points in the National Centers for Disease Control and Prevention.

Results

During the study period, 134,273 malaria cases were reported. The malaria incidence decreased from 0.24/1000 cases in 2002 to 0.01/1000 in 2017. From 2009 onward, the number of imported cases increased in comparison with the autochthonous and indigenous cases. Most cases were seen in males and people over 15 years of age. Moreover, the dominant registered reports were from rural areas. Most malaria cases were reported from the south and southeastern of Iran. Plasmodium vivax was the dominant species.

Conclusion

The dramatic drop in the incidence of autochthonous cases can hopefully support malaria elimination as a major goal in the near future.

Predicting environmentally suitable areas for Anopheles superpictus Grassi (s.l.), Anopheles maculipennis Meigen (s.l.) and Anopheles sacharovi Favre (Diptera: Culicidae) in Iran

BACKGROUND

Malaria is an important mosquito-borne disease, transmitted to humans by Anopheles mosquitoes. The aim of this study was to gather all records of three main malaria vectors in Iran during the last decades, and to predict the current distribution and the environmental suitability for these species across the country.

METHODS

All published documents on An. superpictus Grassi (s.l.), An. maculipennis Meigen (s.l.) and An. sacharovi Favre during 1970-2016 in Iran were obtained from different online data bases and academic libraries. A database was created in ArcMap 10.3. Ecology of these species was analyzed and the ecological niches were predicted using MaxEnt model.

RESULTS

Anopheles superpictus (s.l.) is the most widespread malaria vector in Iran, and exists in both malaria endemic and non-endemic areas. Whereas An. maculipennis (s.l.) is reported from the northern and northwestern parts, Anopheles sacharovi is mostly found in the northwestern Iran, although there are some reports of this species in the western, southwestern and eastern parts. The area under receiver operating characteristic (ROC) curve (AUC) for training and testing data was calculated as 0.869 and 0.828, 0.939 and 0.915, and 0.921 and 0.979, for An. superpictus (s.l.), An. maculipennis (s.l.) and An. sacharovi, respectively. Jackknife test showed the environmental variable with highest gain in the predicting power of the model when used in isolation was annual precipitation for An. superpictus (s.l.) and An. maculipennis (s.l.), and precipitation of the driest quarter for An. sacharovi.

CONCLUSIONS

Despite this range, global warming may increase the potential risk for malaria transmission in some cleared-up areas, where these proven vectors are active. Mapping and prediction of spatial/temporal distribution of these vectors will be beneficial for decision makers to be aware of malaria transmission risk, especially in the western parts of the country.

Wash resistance and bio-efficacy of Olyset® Plus, a long-lasting insecticide-treated mosquito net with synergist against malaria vector, Anopheles stephensi

OBJECTIVE

To determine the wash resistance of Olyset^® Plus using World Health Organization Pesticide Evaluation Scheme standard washing procedure and to assess the value of knock down and mortality rates of Anopheles stephensi at different regimens of long lasting insecticide treated nets washings.

METHODS

The study was conducted at the Bioassay Laboratory of Culicidae Insectary, School of Public Health, Tehran University of Medical Sciences, Iran. The net was made of polyester impregnated with permethrin and piperonyl butoxide at a ratio of 2:1. The washing resistance was assessed using Le Chat^® soap and a shaker incubator set at a speed of 155 r/min, 30 °C for 10 min. The cone bioassay test was carried out according to World Health Organization recommended guideline with tolerant field strain of female Anopheles stephensi to pyrethroids.

RESULTS

The knockdown and mortality rates of female mosquitoes exposed to Olyset^® Plus from un-washed nets to 2 washings were 79.7% and 88.8% respectively. Mortality was dropped to zero while active ingredient estimated 0.532 μg/100 cm² to 0.481 μg/100 cm² after 15 washings. A positive correlation was seen between residues of permethrin on nets, knockdown rate and mortality rate of female Anopheles stephensi exposed to different regimes of washed Olyset^® Plus (r = 0.954, P = 0.001).

CONCLUSIONS

It is recommended that a preliminary survey conducted on resistance level of Anopheles vectors before the distribution of Olyset^® Plus in malaria endemic communities.

Insecticide susceptibility of Anopheles stephensi to DDT and current insecticides in an elimination area in Iran

BACKGROUND

Iran has recently initiated a malaria elimination program with emphasis on vector control strategies which are heavily reliant on indoor residual spraying and long-lasting insecticidal nets. Insecticide resistance seriously threatens the efficacy of vector control strategies. This study was conducted to determine the insecticide susceptibility of Anopheles stephensi to DDT and current insecticides in Jask county as an active malaria focus in southeastern Iran.

METHODS

In this study, the anopheline larvae were collected from different aquatic habitats in Jask county and transported to insectarium, fed with sugar and then 3-day-old adults were used for susceptibility tests. WHO insecticide susceptibility tests were performed with DDT (4 %), malathion (5 %), lambda-cyhalothrin (0.05 %), deltamethrin (0.05 %) and permethrin (0.75 %).

RESULTS

The field strain of An. stephensi was found resistant to DDT and lambda-cyhalothrin. The LT50 values for DDT and lambda-cyhalothrin in this species were 130.25, and 37.71 min, respectively. Moreover, An. stephensi was completely susceptible to malathion and permethrin and tolerant to deltamethrin.

CONCLUSION

The present study results confirm the resistance of the major malaria vector, An. stephensi, to DDT and lambda-cyhalothrin, and tolerance to deltamethrin, which could gradually increase and spread into other malaria endemic areas. Thus, there is a need for regular monitoring of insecticide resistance in order to select suitable insecticides for vector control interventions towards malaria elimination.

Molecular characterization, biological forms and sporozoite rate of Anopheles stephensi in southern Iran

OBJECTIVE

To identify the biological forms, sporozoite rate and molecular characterization of the Anopheles stephensi (An. stephensi) in Hormozgan and Sistan-Baluchistan provinces, the most important malarious areas in Iran.

METHODS

Wild live An. stephensi samples were collected from different malarious areas in southern Iran. The biological forms were identified based on number of egg-ridges. Molecular characterization of biological forms was verified by analysis of the mitochondrial cytochrome oxidase subunit I and II (mtDNA-COI/COII). The Plasmodium infection was examined in the wild female specimens by species-specific nested-PCR method.

RESULTS

Results showed that all three biological forms including mysorensis, intermediate and type are present in the study areas. Molecular investigations revealed no genetic variation between mtDNA COI/COII sequences of the biological forms and no Plasmodium parasites was detected in the collected mosquito samples.

CONCLUSIONS

Presence of three biological forms with identical sequences showed that the known biological forms belong to a single taxon and the various vectorial capacities reported for these forms are more likely corresponded to other epidemiological factors than to the morphotype of the populations. Lack of malaria parasite infection in An. stephensi, the most important vector of malaria, may be partly due to the success and achievement of ongoing active malaria control program in the region.

Some ecological attributes of malarial vector Anopheles superpictus Grassi in endemic foci in southeastern Iran

OBJECTIVE

To determine the bionomics and susceptibility status of the malarial vector Anopheles superpictus (An. superpictus) to different insecticides in the Sistan-Baluchestan province which has the highest malarial prevalence in Iran.

METHODS

Different sampling methods, in addition to scoring abdominal conditions, were used to define the seasonal activity and endo/exophilic behavior of this species. In addition, the standard WHO susceptibility tests were applied on adult field strains.

RESULTS

Most adult mosquitoes were collected from outdoor shelters. The peak of seasonal activity of An. superpictus occurred at the end of autumn. Most larvae were collected from natural and permanent breeding places with full sunlight and no vegetation. Blood feeding activities occurred around midnight. Compared with the abdominal conditions of adult mosquitoes collected indoors, the abdominal conditions of adult mosquitoes collected outdoors were gravid and semigravid. This species was suspected to be resistant to DDT, but was susceptible to other insecticides.

CONCLUSIONS

An. superpictus was present in almost all outdoor shelters, and the ratios of gravid, semigravid/unfed, and freshly fed confirmed that this species had a higher tendency to rest outdoors than indoors. This behavior can protect An. superpictus from indoor residual spraying in this malarious area. To the best of our knowledge, this is the first report on the susceptibility status of An. superpictus in Southeastern Iran. We do not suggest the use of DDT for indoor residual spraying in southeast Iran.