Malaria Vector Control Programmes Research Articles

Transcriptomic analysis of Anopheles gambiae from Benin reveals overexpression of salivary and cuticular proteins associated with cross-resistance to pyrethroids and organophosphates

BackgroundInsecticide resistance (IR) is one of the major threats to malaria vector control programs in endemic countries. However, the mechanisms underlying IR are poorly understood. Thus, investigating gene expression patterns related to IR can offer important insights into the molecular basis of IR in mosquitoes. In this study, RNA-Seq was used to characterize gene expression in Anopheles gambiae surviving exposure to pyrethroids (deltamethrin, alphacypermethrin) and an organophosphate (pirimiphos-methyl).ResultsLarvae of An. gambiae s.s. collected from Bassila and Djougou in Benin were reared to adulthood and phenotyped for IR using a modified CDC intensity bottle bioassay. The results showed that mosquitoes from Djougou were more resistant to pyrethroids (5X deltamethrin: 51.7% mortality; 2X alphacypermethrin: 47.4%) than Bassila (1X deltamethrin: 70.7%; 1X alphacypermethrin: 77.7%), while the latter were more resistant to pirimiphos-methyl (1.5X: 48.3% in Bassila and 1X: 21.5% in Djougou). RNA-seq was then conducted on resistant mosquitoes, non-exposed mosquitoes from the same locations and the laboratory-susceptible An. gambiae s.s. Kisumu strain. The results showed overexpression of detoxification genes, including cytochrome P450s (CYP12F2, CYP12F3, CYP4H15, CYP4H17, CYP6Z3, CYP9K1, CYP4G16, and CYP4D17), carboxylesterase genes (COEJHE5E, COE22933) and glutathione S-transferases (GSTE2 and GSTMS3) in all three resistant mosquito groups analyzed. Genes encoding cuticular proteins (CPR130, CPR10, CPR15, CPR16, CPR127, CPAP3-C, CPAP3-B, and CPR76) were also overexpressed in all the resistant groups, indicating their potential role in cross resistance in An. gambiae. Salivary gland protein genes related to ‘salivary cysteine-rich peptide’ and ‘salivary secreted mucin 3’ were also over-expressed and shared across all resistant groups.ConclusionOur results suggest that in addition to metabolic enzymes, cuticular and salivary gland proteins could play an important role in cross-resistance to multiple classes of insecticides in Benin. These genes warrant further investigation to validate their functional role in An. gambiae resistance to insecticides.

First Observations of Plasmodium malariae on the Long-Term Malaria Vector Control Program on Villages of the Balombo Region of Angola

First Observations of Plasmodium malariae on the Long-Term Malaria Vector Control Program on Villages of the Balombo Region of Angola

Mitotic metaphase karyotype of the mosquito Anopheles arabiensis Patton (Diptera: Culicidae) from Kassala State, eastern Sudan

The mosquito Anopheles arabiensis Patton is the most important malaria vector in Sudan. The study was conducted for the first time to describe numerically the karyotype of An. arabiensis from Kassala State, eastern Sudan. Adults An. arabiensis were caught from human dwellings during the rainy season of 2022. We examined for the first time the utility of brain ganglia tissues of adult mosquitoes for mitotic chromosomal preparations using Giemsa stain - spreading technique. High-quality chromosomal preparations were examined and photographed. Chromosome measurements were carried out using computer software and analyzed statistically using SPSS® software. The diploid mitotic chromosome complement of An. arabiensis consists of three pairs of chromosomes, two pairs of metacentric autosomes (chromosome II and chromosome III) and one acrocentric dot-shaped pair, sex chromosome, which is homomorphic in females (XX) and heteromorphic in males (XY). Chromosome II was described as the longest (2.61±0.07) of the complement and constitute 44.39% of the total length (5.88 μm) of the haploid chromosomes set, while chromosome I (X=1.39 ±0.04; Y=1.04±0.04) as the shortest chromosome. Chromosome X appears in the males significantly larger than chromosome Y (P = 0.00). Chromosome III has an intermediate length (1.88±0.06) compared with the other chromosomes. Comparison of the average lengths of the three chromosome pairs by ANOVA test revealed highly statistical significant differences between them (P < 0.00). The study establishes a strong cytogentic data, which can contribute to accurate identification of the mosquito An. arabiensis and to planning human malaria vector control programs in Kassala State, eastern Sudan.

Challenges in Understanding the Bionomics of Indian Malaria Vectors.

Many factors influence the success or failure of malaria vector control program such as political will, leadership, sustained funding, robustness of healthcare system and others. In addition, updated knowledge and information about the triad of host, parasite, and vector is of paramount importance. Vector bionomics studies that determine mosquito behavior in terms of feeding, resting, biting, mating, breeding, longevity, vectorial capacity, and response to different insecticides are a step towards enhancing our understanding. In the present work, we have compiled studies conducted in India over the past two decades (2000-2020) to identify gaps in our knowledge of malaria vector bionomics and the research that needs to be done in the future. We retrieved district-level data of India's six primary malaria vector species. According to our findings, vector bionomics studies have been undertaken in ∼50% and ∼15% of the country's high (annual parasite index >1) and low (annual parasite index <1) malaria-endemic districts respectively. Most of the research studies focused on mosquito density, insecticide susceptibility status, and parasite detection, whereas other vital bionomics parameters were neglected. Surveys conducted were incomplete, and vector bionomics data were not captured sufficiently. The absence of vector bionomics data can be a blind spot and the lack or inadequate understanding of vector bionomics can lead to use of inappropriate vector control tools. Thus, there is an urgent need to initiate comprehensive bionomics studies on India's primary and secondary malaria vectors.

Insecticide Susceptibility Status of Anopheles and Aedes Mosquitoes in Malaria and Dengue Endemic Areas, Thai–Myanmar Border

The occurrence and spread of insecticide resistance has had a negative effect on the efficacy of insecticide-based tools and is distributed worldwide, including the Greater Mekong Subregion (GMS). This study aims to determine the insecticide susceptibility of malaria and dengue vectors in malaria and dengue hotspots on the Thai-Myanmar border. Mosquito larvae and pupae were obtained from water sources from December 2019 to April 2020 in Tha Song Yang District, Tak province, western Thailand. WHO bioassay susceptibility tests were conducted with three classes of insecticides to evaluate the knockdown and mortality rates of Anopheles and Aedes aegypti female adults. V1016G and F1534C kdr mutations in the voltage-gated sodium channel of Ae. aegypti were identified using a multiplex PCR. A total of 5764 female mosquitoes were bioassayed in this study, including Anopheles spp. (92.63%) and F1 Ae. aegypti (7.37%). After 24 h of observation, An. minimus s.l. (n = 3885) and An. maculatus s.l. (n = 1138) in Suan Oi (SO) and Tala Oka (TO) were susceptible to pyrethroids, organophosphates and carbamates (except bendiocarb) with 98-100% mortality (MR). Resistance to bendiocarb was detected with a mortality rate of 88.80%, 88.77%, and 89.92% for An. minimus s.l. (n = 125, 125) and An. maculatus s.l. (n = 66), respectively. The first generation of Ae. aegypti adult females were suspected of resistance to deltamethrin (n = 225, MR = 96.89%) and confirmed resistance to permethrin (n = 200, MR = 20.00%). V1016G and F1534C mutations were detected in three genotypes, heterozygote and homozygote forms. The correlation between the kdr alleles and deltamethrin resistance was significant. In conclusion, bendiocarb resistance was found in primary malaria vectors, An. minimus s.l. and An. maculatus s.l. F1 Ae. aegypti population was pyrethroids-resistant, associated with kdr alleles. Therefore, molecular analysis should be conducted to gain insights into the mechanism of insecticide resistance. Routine malaria vector control programmes, such as fogging implementation in hotspot villages to induce Aedes resistance available in peri-domestic sites, are questionable.

Potential of Essential Oil-Based Anticholinesterase Insecticides against Anopheles Vectors: A Review.

The insect nervous system is critical for its functional integrity. The cholinergic system, of which acetylcholinesterase (AChE) is a key enzyme, is essential to the Anopheles (consisting of major malaria vector species) nervous system. Furthermore, the nervous system is also the primary target site for insecticides used in malaria vector control programs. Insecticides, incorporated in insecticide-treated nets and used for indoor residual spraying, are a core intervention employed in malaria vector control. However, Anopheles resistance against these insecticides has grown rapidly. Due to this major setback, novel agents with potential activity against resistant Anopheles and/or capacity to overcome resistance against current WHO-approved insecticides are urgently needed. The essential oils have the potential to be natural sources of novel insecticides with potential to inhibit the Anopheles AChE target. In the current review, the scientific evidence highlights the ability of essential oils and specific essential oil constituents to serve as anticholinesterase insecticides. For this reason, the published data from scientific databases on the essential oils and essential oil constituents on anticholinesterase, ovicidal, larvicidal, pupicidal and adulticidal activities were analyzed. The identification of major constituents in active essential oils and their possible influence on the biological activity have also been critically evaluated. Furthermore, the toxicity to mammals as well as potential activity against the mammalian AChE target has also been reviewed. The importance of identifying novel potent insecticides from essential oils has been discussed, in relation to human safety and cost-effectiveness. Finally, the critical insights from this review can be used to inform future researchers towards potent and safe anticholinesterase insecticides for the management of Anopheles malaria vectors.

Malaria vector bionomics and transmission in irrigated and non-irrigated sites in western Kenya

Irrigation not only helps to improve food security but also creates numerous water bodies for mosquito production. This study assessed the effect of irrigation on malaria vector bionomics and transmission in a semi-arid site with ongoing malaria vector control program. The effectiveness of CDC light traps in the surveillance of malaria vectors was also evaluated relative to the human landing catches (HLCs) method. Adult mosquitoes were sampled in two study sites representing irrigated and non-irrigated agroecosystems in western Kenya using a variety of trapping methods. The mosquito samples were identified to species and assayed for host blood meal source and Plasmodium spp. sporozoite infection using polymerase chain reaction. Anopheles arabiensis was the dominant malaria vector in the two study sites and occurred in significantly higher densities in irrigated study site compared to the non-irrigated study site. The difference in indoor resting density of An. arabiensis during the dry and wet seasons was not significant. Other species, including An. funestus, An. coustani, and An. pharoensis, were collected. The An. funestus indoor resting density was 0.23 in irrigated study site while almost none of this species was collected in the non-irrigated study site. The human blood index (HBI) for An. arabiensis in the irrigated study site was 3.44% and significantly higher than 0.00% for the non-irrigated study site. In the irrigated study site, the HBI of An. arabiensis was 3.90% and 5.20% indoor and outdoor, respectively. The HBI of An. funestus was 49.43% and significantly higher compared to 3.44% for An. arabiensis in the irrigated study site. The annual entomologic inoculation rate for An. arabiensis in the irrigated study site was 0.41 and 0.30 infective bites/person/year indoor and outdoor, respectively, whereas no transmission was observed in the non-irrigated study site. The CDC light trap performed consistently with HLC in terms of vector density. These findings demonstrate that irrigated agriculture may increase the risk of malaria transmission in irrigated areas compared to the non-irrigated areas and highlight the need to complement the existing malaria vector interventions with novel tools targeting the larvae and both indoor and outdoor biting vector populations.Graphical abstract

The Durable Lining: A New Tool for Malaria Vector Control Compared to Other Classical Methods (Long Lasting Insecticide Treated Nets “LLIN” During a Village Scale Long Term Trial in Angola. I. Entomological Evaluation.

Background: Deltamethrin (“δ”) treated durable lining (“DL”) or “insecticide treated plastic sheeting” (“δITPS”) were used for a long term village–scale malaria vector control (VC) program in 8 villages around Balombo town

Plasmodial Prevalence with Respect to Gender in 6 Villages Around Balombo Town, Benguela Province, Angola, before Malaria Vector Control Implementation

Background: The different susceptibility of gender to infectious diseases is still a matter of concern and several studies were devoted to these issues; for malaria, recent studies reported a comparable “Force of Infection” in both gender while women could have a faster elimination of parasite than men.&#x0D; Study Area and duration Period of the Research: The study was done in villages around Balombo town, Benguela Municipality, Angola and initially scheduled for 5 years since year 2007 with 2 years before vector control implementation and 3 years after.&#x0D; Objectives of the research. The village scale malaria vector control program was planned and implemented to compare 4 methods of vector control with comprehensive entomological and parasitological evaluation, focusing on symptomless randomly selected patients, and noticing age and gender during each field survey for further analysis.&#x0D; Study Design: To check an eventual gender difference, we decided to analyze the parasitological data gained during the 56 cross sectional surveys (CSS) done during 2 consecutive years in the 6 villages used as “control” i.e. before implementation of vector control operations (VCO) considering the gender of symptomless patients (≤15 years old) surveyed. We considered 2 indicators: Plasmodial Prevalence (PP) and Parasite Load (PL).&#x0D; Main Results: 6727 thick blood smears (TBS) were prepared during these 56 CSS, and microscopically examined; the sex ratio of this total sample was well balanced with 3406 TBS (=50.6%) from men (“M”) and 3321 TBS (49.4%) from women (W”). The overall Plasmodial prevalence (all Plasmodium sp gathered because P. falciparum infections, as already noticed, are largely preponderant) were similar 41.02% for M and 40.1% for W.&#x0D; The overall plasmodial prevalence significantly decreased from Year 2007 to Year 2008: respectively 47.8% (n= 2686) and 35.7% (n= 4041); but the plasmodial prevalence were similar each year between gender: in year 2007: PP= 48.9% (n=1338) for M and 46.7% (n= 1348) for W and in year 2008: 35.9% (n=2068) for Men and 35.6% (n=1973) for Women.&#x0D; In Year 2007 the PP of Men and Women were similar in each village; in Year 2008 the PP were similar in 5 villages, but in Libata PP was significantly higher in Men than in Women.&#x0D; The trends of change from year to year appeared similar for gender excepted in Capango where the PP remained similar in W and significantly decreased for M.&#x0D; In term of Parasite Load the comparison of median of parasitaemia with the non-parametric Mann-Whitney test showed similar distribution between gender each year in each village and their evolution from year to year appeared also similar in each gender excepted for Men in Libata.&#x0D; Conclusion: These possibilities of changes of plasmodial infections according to gender with time and villages must be taken into consideration when planning, implementing and analyzing parasitological data of symptomless carriers before, and after, a vector control program which must be implemented on a long term basis. They show that an “only one” CSS could lead to wrong information and conclusion of malaria and gender and the recommendation to carry on longitudinal regular field studies for relevant conclusion on malaria infections among communities.&#x0D; The next step will be to analyze the plasmodial infection in both gender after vector control implementation.

Long-term evolution of Plasmodium falciparum gametocytes index during a village scale malaria vector control program comparing durable lining, long-lasting treated net and indoor residual spraying in Angola

Rationale: Due to the serious side effect of some anti-gametocyte drugs on G6PG efficiency carriers, a special attention was given to the possible influence of vector control on the evolution of P. falciparum gametocyte index (GI) in the framework of the long-term village scale malaria vector control project implemented in 8 villages around the Balombo town (Angola). The aim of the project was to compare, in paired villages, the epidemiological efficacy of Long lasting deltamethrin Insecticide Treated Nets (δLLIN), lambdacyhalothrin Inside Residual Spraying (ʎIRS), and deltamethrin Insecticide Treated Plastic Sheeting (δITPS) applied on the indoor walls of houses, used alone, or associated with δLLIN or after the 2 rounds of λIRS. Methods: The program started in 2007 and full vector control (VC) implementation was done in December 2008 owing two years of baseline data collection in the 8 selected villages around Balombo city. Parasitological evaluation was based upon regular cross-sectional surveys (CSS) on randomized samples of population for each survey, focusing ≤ 15 years children, to compare GI before/after and here/there according to each VC method. Field made thick blood smears (TBS) were microscopically examined by the same team of the Medical Department of the Angolese Sonamet Company, which supported the trial, with 10% of randomized slides double-checked in OCEAC, Yaoundé (Cameroon). Results: 234 cross-sectional surveys were carried between 2007 and 2018. P. falciparum gametocytes were observed in 574 of the 23,822 thick blood smears examined for a GI of 2.41%. During the 3 years following the VC full implementation, the GI decreased by 71%, from 4.05% (n= 6,697) before VC to 1.17% (n= 7,667 after VC) with similar influence of each VC method. During the 5 following years GI remained at a very low level (0.23%; n=2,992). Due to the national malaria outbreak, an increase was noticed after 2015. The general CSS survey done in February 2018, 11 years after the first one (February 2007), showed in the same 5 villages a significant 80% decrease of GI, from 6.98% (n=773) to 1.42% (n=421). Conclusion: The trial showed that a long-term malaria village scale vector control program had a long lasting and significant impact on P. falciparum gametocytes and the influence of VC on GI could therefore be recommended as another relevant objective of the National Malaria Control Program.

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.

Population genetics of Anopheles arabiensis, the primary malaria vector in the Republic of Sudan

BackgroundAnopheles arabiensis is a member of Anopheles gambiae complex and the main malaria vector in Sudan. There is insufficient population genetics data available on An. arabiensis for an understanding of vector population structure and genetics, which are important for the malaria vector control programmes in this country. The objective of this investigation is to study the population structure, gene flow and isolation by distance among An. arabiensis populations for developing control strategies.MethodsMosquitoes were collected from six sites located in three different states in Sudan, Khartoum, Kassala and Sennar, using pyrethrum spray catch of indoor resting mosquitoes. Anopheline mosquitoes were identified morphologically and based on species specific nucleotide sequences in the ribosomal DNA intergenic spacers (IGS). Seven published An. gambiae microsatellite loci primers were used to amplify the DNA of An. arabiensis samples.ResultsPCR confirmed that An. arabiensis was the main malaria vector found in the six localities. Of the seven microsatellite loci utilized, six were found to be highly polymorphic across populations, with high allelic richness and heterozygosity with the remaining one being monomorphic. Deviation from Hardy–Weinberg expectations were found in 21 out of 42 tests in the six populations due to heterozygote deficiency. Bayesian clustering analysis revealed two gene pools, grouping samples into two population clusters; one includes four and the other includes two populations. The clusters were not grouped according to the three states but were instead an admixture. The genetic distances between pairs of populations ranged from 0.06 to 0.24. Significant FST was observed between all pairwise analyses of An. arabiensis populations. The Kassala state population indicated high genetic differentiation (FST ranged from 0.17 to 0.24) from other populations, including one which is also located in the same state. High gene flow (Nm = 1.6–8.2) was detected among populations within respective clusters but limited between clusters particularly with respect to Kassala state. There was evidence of a bottleneck event in one of the populations (Al Haj Yousif site). No isolation by distance pattern was detected among populations.ConclusionsThis study revealed low levels of population differentiation with high gene flow among the An. arabiensis populations investigated in Sudan, with the exception of Kassala state.

Pyrethroid Resistance in Anopheles gambiae Not Associated with Insecticide-Treated Mosquito Net Effectiveness Across Sub-Saharan Africa.

Pyrethroid resistance is a major concern for malaria vector control programs that predominantly rely on insecticide-treated mosquito nets (ITNs). Contradictory results of the impact of resistance have been observed during field studies. We combined continent-wide estimates of pyrethroid resistance in Anopheles gambiae from 2006 to 2017, with continent-wide survey data to assess the effect of increasing pyrethroid resistance on the effectiveness of ITNs to prevent malaria infections in sub-Saharan Africa. We used a pooled-data approach and a meta-regression of survey regions to assess how pyrethroid resistance affects the association between ITN ownership and malaria outcomes for children 6 to 59 months of age. ITN ownership reduced the risk of malaria outcomes according to both the pooled and meta-regression approaches. According to the pooled analysis, there was no observed interaction between ITN ownership and estimated level of pyrethroid resistance (likelihood ratio [LR] test, 1.127 for malaria infection confirmed by the rapid diagnostic test, P = 0.2885; LR test = 0.161 for microscopy-confirmed malaria infection, P = 0.161; LR test = 0.646 for moderate or severe anemia, P = 0.4215). Using the meta-regression approach to determine the level of pyrethroid resistance did not explain any of the variance in subnational estimates of ITN effectiveness for any of the outcomes. ITNs decreased the risk of malaria independent of the levels of pyrethroid resistance in malaria vector populations.

Co-Evolution of the Presence of Long Lasting Insecticide Treated Nets and Plasmodium falciparum Welch, 1897 Prevalence in Cahata Village (Benguela Province, Angola) during a Village Scale Long-Term of Malaria Vector Control Program

A long term village scale vector control programme was implemented since 2007 in 8 villages around Balombo town (Benguela Province) to compare the efficacy of 4 methods of vector control (1,2). One of them are deltamethrin treated Long Lasting Nets (“LLIN”) “Perma©Net 2.0” with a complete coverage of every sleeping units in 2008 in 2 villages, Caala and Cahata. Cahata was surveyed for 10 years with regular parasitological cross sectional parasitological surveys. During the 3 years following LLIN implementation, a check of their actual usage in every house, or on sleeping units of each patient examined during every parasitological surveys showed that 3 years after the full LLIN distribution less than 50% were still in use, and this percentage regularly decreased to reach 10% and less in 2015 (with 0% during the survey done in October 2005). But Plasmodium falciparum prevalence still decreased with low level until 2014 then it started (slightly) increasing in 2015, and the following years, which correspond to both the National malaria outbreak and the least percentage of LLIN used! But even at that time the plasmodial load was significantly lower in “LLIN users” than in non users showing some maintained personal protection.&#x0D; Even 10 years after the full coverage in LLIN no rebound effect was actually noticed in such natural conditions of life and plasmodial prevalence was even 2 times lower than before the implementation of vector control.&#x0D; Information gained were of great importance for the National Malaria Control program in term of nets replacement with 50% missing in 3 years underlining the need of “stronger” nets and community sensitization for the sustainability of positive results gained with LLIN.

Evaluation of the « Time/Risk » Probability of being Infected and its Evolution Before/After a Long Term Village Scale Malaria Vector Control Programme in Angola

Three main entomological indicators are classically used in the epidemiology of malaria: the inoculation rate (“h”) of Ross, the vectorial capacity (“C”) of Garrett-Jones and the reproduction rate (“z”) of Macdonald. In spite of their undoubtfully usefulness it appeared that their formulae did not integrate the key parameter of “t” i.e. the time of exposure and therefore the probabilities of being infected according to the entomological condition (density, infectivity, longevity of the vectors) but also the time/risk and the reduction of this risk when some village-scale vector control measures are implemented.&#x0D; To deal with this approach we used the Briley’s formula, elaborated some years ago, to analyze the time/risk of being infected in the framework of a long term village scale vector control programme implemented around Balombo (Benguela Province, Angola) with classical method (inside residual spraying) and newly developed tool s (insecticide treated plastic sheeting) used alone or in association with the classical long lasting insecticide treated nets.&#x0D; Before vector control the risk was almost 20% in one week, 60% in one month and 100% in 3 months and this explain why plasmodic index are so high in this area without any organized vector control programme.&#x0D; The 3 methods actually reduced the risks which become of the order of 2% in one week, 10% in one month, 26% in one trimester but 70% in one year; the three methods had the same efficacy in reducing these risks. The fact that the risk reach 70% in one year even with right vector control shows the needs of renewing regularly the operations, the needs of other than entomological methods of prevention but also that immunity could be maintained and feared “rebound” was not observed even during the long term of the programme.

Characterization of resistance profile (intensity and mechanisms) of Anopheles gambiae in three communes of northern Benin, West Africa

BackgroundThe selection and the spread of insecticide resistance in malaria vectors to the main classes of insecticides used in vector control tools are a major and ongoing challenge to malaria vector control programmes. This study aimed to determine the intensity of vector resistance to insecticides in three regions of Benin with different agro-ecological characteristics.MethodsLarvae of Anopheles gambiae sensu lato (s.l.) were collected from September to November 2017 in different larval sites in three northern Benin communes: Parakou, Kandi and Malanville. Two to five-day-old, non-blood-fed, female mosquitoes were exposed to papers impregnated with deltamethrin, permethrin and bendiocarb at dosages of 1 × the diagnostic dose, 5 × and 10 × to determine the intensity of resistance in these vectors. Molecular frequencies of the kdr L1014F and ace-1R G119S insecticide resistance mutations and levels of detoxification enzymes were determined for mosquitoes sampled at each study site.ResultsResistance to pyrethroids (permethrin and deltamethrin) was recorded in all three communes with mortality rates below 60% using the diagnostic dose (1x). The results obtained after exposure of An. gambiae to permethrin 10 × were 99% in Kandi, 98% in Malanville and 99% in Parakou. With deltamethrin 10x, mortality rates were 100% in Kandi, 96% in Malanville and 73% in Parakou. For the diagnostic dose of bendiocarb, suspected resistance was recorded in the communes of Malanville (97%) and Kandi (94%) while sensitivity was observed in Parakou (98%).Using the 10 × dose, mortality was 98% in Kandi, 100% in Malanville and 99% in Parakou. The frequencies of the kdr L1014F allele varied between 59 and 83% depending on the sites and species of the An. gambiae complex, while the frequency of the ace-1R G119S gene varied between 0 and 5%. Biochemical tests showed high levels of oxidase and esterase activity compared to the susceptible colony strain of An. gambiae sensu stricto (Kisumu strain).ConclusionAnopheles gambiae showed a generalized loss of susceptibility to permethrin and deltamethrin but also showed moderate to high intensity of resistance in different regions of Benin. This high intensity of resistance is a potential threat to the effectiveness of vector control.

Distribution and The Habitat Characteristics of Anopheles vagus (Diptera: Culicidae) Larvae at Paddy Fields in The Vicinity of Dramaga IPB University Campus Dramaga Bogor West Java

Dramaga sub-district is an area that has rice fields close to buffalo stalls and a population of wild Macaca fascicularis as natural hosts for several species of Plasmodium. This causes the Dramaga sub-district to become a potential vector habitat for malaria, including Anopheles vagus. This study aims to analyze distribution of An. vagus larval stage in 4 villages (Cikarawang, Babakan, Margajaya, and Ciherang) in Dramaga subdistrict which have paddy field areas. Larvae were collected using a dipper, and each collection sites of the larvae habitat were marked using Global Positioning System. The physical characteristics of the water habitat measured were temperature, pH, total dissolved solids and the electrical conductivity of the water. Pearson's correlation test was used to analyze the relationship between the number of larvae An. vagus with each of the parameters water physical characteristics. The results of this study obtained 309 An. vagus larvae from the 27 collection points. Larvae of An. vagus was found in 3 villages (i.e. Cikarawang, Babakan and Ciherang), but was not found in Margajaya village. The habitat characteristics of An. vagus in paddy fields showed a water temperature of 26.6-31.7oC, pH 6.40-8.10, the total dissolved solid 36-285 ppm, and the electrical conductivity 72-262 μm/cm. The Pearsons correlation test results did not show a significant difference between the number of An. vagus larvae and each parameter (r= -0.26, 0.13, -0.15 and -0.16, respectively). The presence of An. vagus in this area could be considered in malaria vector control programs.

Lessons from the Malaria Vector Control Program Based on Indoors Residual Spraying with DDT or Dieldrin in the Pilot Zone of Bobo-Dioulasso: Failure or Success?

RésuméPendant cinq ans, à partir de 1953, un grand programme d'aspersions pariétales intradomiciliaires s'est déroulé dans la zone pilote de Bobo-Dioulasso avec du DDT ou de la dieldrine (DLN) avec une évaluation conceptuellement entomologique et parasitologique [18].Par rapport à la zone témoin, le DDT a induit une réduction d'environ 95% et 67% du taux de piqûres d'Anopheles gambiae, respectivement à l'intérieur et à l'extérieur des maisons. Mais du fait de son action irritante, le DDT a augmenté de cinq fois le coefficient d'exophagie de ce vecteur. La DLN n'a eu aucun impact sur le taux de piqûres d'An. gambiae aussi bien à l'intérieur qu'à l'extérieur, vu la résistance de l'espèce anophélienne à cet insecticide. L'indice sporozoïtique d'An. gambiae a été réduit de 96% dans les zones traitées au DDT et de 70% dans le secteur traité à la DLN.Le DDT a réduit de 98% et de 91% le taux de piqûres d'Anopheles funestus, respectivement dans les maisons traitées et à l'extérieur. Avec la DLN, ces réductions ont été respectivement de 98% et 97%. L'indice sporozoïtique d'An. funestus a été réduit de 95% dans les zones traitées au DDT.La lutte antivectorielle a permis de réduire la transmission due à An. gambiae et An. funestus de quelques 99,8% dans les villages traités au DDT par rapport aux villages témoins. La DLN a permis de réduire de 99,9% la transmission due à An. funestus, mais quasiment pas celle due à An. gambiae . La lutte antivectorielle basée sur les aspersions intradomiciliaires de DDT ou de DLN a permis de réduire de 99,9% la transmission des Plasmodium humains assurée par les deux vecteurs majeurs, An. gambiae et An. funestus dans les villages de la zone pilote.Chez les enfants de 2–9 ans l'indice splénique a été de 84,3% (n= 979) en zone témoin et 44,4% (n = 8920) en zones traitées (différence: -47,3%), la prévalence plasmodiale a été de 60,6% (n = 946) en zone témoin et 38,0% (n = 7242) en zones traitées (différence: – 37%) mais les indices gamétocytiques sont restés aux mêmes niveaux (3,28%, n = 946 en zone témoin et 3,04%, n = 7242 en zones traitées) indiquant le maintien du « réservoir de virus » et des possibilités de transmission.Par rapport à la zone témoin, « l'indice de contamination nouvelle » a été significativement moindre chez les nourrissons de 0-3 mois et de 4 à 6 mois dans les villages traités au DDT mais pas chez les nourrissons 7 à 12 mois démontrant que la lutte antivectorielle avait eu une certaine efficacité dans la prévention de l'infection plasmodiale mais « tous les nouveau-nés étaient infectés dans l'année », donc la transmission de P. falciparum n'avait pas été complètement stoppée.Les aspersions intradomiciliaires avec le DDT ont été d'une grande efficacité dans la réduction de la transmission mais les vecteurs sont restés présents et la transmission, même fortement réduite, s'est maintenue de sorte que dans l'optique de l'éradication, le programme avait été considéré comme un « semi–échec » avec la décision d'adopter un changement complet de stratégie de lutte contre le paludisme et de se centrer sur la chimiothérapie de masse plutôt que sur la lutte antivectorielle.Ces opérations de lutte antivectorielle d'aspersions pariétales de DDT peuvent être considérées comme un succès entomologique, avec ses limites indiquées par le maintien d'un certain niveau de transmission et des indices spléniques et plasmodiques ainsi que d'une incidence observée chez les nourrissons. Cinquante ans après, en l'absence de vaccins, cette recommandation de lutte intégrée et coordonnée contre les vecteurs et les Plasmodium est toujours d'actualité en bénéficiant, entre autres, des moustiquaires imprégnées et des traitements à base d'artémisine.

Outdoor residual spray for the control of monkey malaria vectors in Sarawak, Malaysia

The increase in cases of monkey malaria in humans, especially in Malaysia Borneo which is believed to be due to infection by the malaria vector that took place outdoor, shows the importance of outdoor residual spraying in controlling this vector. This study aims to evaluate the effectiveness of the new formulation deltamethrin K-Othrine® (PolyZone) and examine its suitability in the control of knowlesi malaria vector in Sarawak, in comparison to deltamethrin K-Othrine® WG250 wettable granule, the insecticide currently use in the vector control programme. The study was performed at three sites in Sarawak having similar type of houses made out of wood and concrete. Houses of two sites were sprayed outdoor with deltamethrin K-Othrine® (PolyZone) at two different dosages, one site with 25 mg/m2 and the other site with 30 mg/m2. Houses of the third site (control house) were sprayed indoor with deltamethrin K-Othrine® WG 250 wettable granule at 25 mg/m2. Residual activity on different walls was assessed using WHO standard cone bioassay techniques. For vector surveillances, larvae and adult surveillance were conducted pre and post spraying. Nested and semi-nested PCR was conducted to detect the malaria parasite in adult mosquitoes. Outdoor residual sprayed of Deltamethrin K-Othrine® (PolyZone) presented higher efficacy compared to indoor residual sprayed of Deltamethrin K-Othrine® WG 250. The efficacy of different type of wall surfaces (wood and concrete) was found varied. Deltamethrin K-Othrine® (PolyZone) at 30 mg/m2 was the most effective with regards to ability to cause higher mortality. Spraying activity conducted during this study, has resulted in malaria cases in Julau reduced significantly. Based on findings of this study, it is recommended to consider outdoor residual spraying on wall surfaces in the community for improved effectiveness of malaria vector control programme.

New assessment of Anopheles vector species identification using MALDI-TOF MS

BackgroundAnopheles species identification is essential for an effective malaria vector control programme. Matrix-assisted laser desorption ionization-time of flight (MALDI-TOF) mass spectrometry (MS) has been developed to identify adult Anopheles species, using the legs or the cephalothorax. The protein repertoire from arthropods can vary according to compartment, but there is no general consensus regarding the anatomic part to be used.MethodsTo determine the body part of the Anopheles mosquitoes best suited for the identification of field specimens, a mass spectral library was generated with head, thorax with wings and legs of Anopheles gambiae, Anopheles arabiensis and Anopheles funestus obtained from reference centres. The MSL was evaluated using two independent panels of 52 and 40 An. gambiae field-collected in Mali and Guinea, respectively. Geographic variability was also tested using the panel from Mali and several databases containing added specimens from Mali and Senegal.ResultsUsing the head and a database without specimens from the same field collection, the proportion of interpretable and correct identifications was significantly higher than using the other body parts at a threshold value of 1.7 (p < 0.0001). The thorax of engorged specimens was negatively impacted by the blood meal after frozen storage. The addition of specimens from Mali into the database significantly improved the results of Mali panel (p < 0.0001), which became comparable between head and legs. With higher identification scores, the using of the head will allow to decrease the number of technical replicates of protein extract per specimen, which represents a significant improvement for routine use of MALDI-TOF MS.ConclusionsThe using of the head of Anopheles may improve the performance of MALDI-TOF MS. Region-specific mass spectrum databases will have to be produced. Further research is needed to improve the standardization in order to share online spectral databases.