scholarly journals Species Composition, Phenotypic and Genotypic Resistance Levels in Major Malaria Vectors in Teso North and Teso South Subcounties in Busia County, Western Kenya

2020 ◽  
Vol 2020 ◽  
pp. 1-17 ◽  
Author(s):  
Edward K. Githinji ◽  
Lucy W. Irungu ◽  
Paul N. Ndegwa ◽  
Maxwell G. Machani ◽  
Richard O. Amito ◽  
...  
Keyword(s):  
Species Composition ◽  
Insecticide Resistance ◽  
Anopheles Gambiae ◽  
Selection Pressure ◽  
Sensu Stricto ◽  
Allelic Frequency ◽  
Assay Method ◽  
Genotypic Frequency ◽  
Western Kenya ◽  
Significant Difference

Introduction. Knockdown resistance (kdr) is strongly linked to pyrethroid insecticide resistance in Anopheles gambiae in Africa, which may have vital significance to the current increased use of pyrethroid-treated bed net programmes. The study is aimed at determining species composition, levels of insecticide resistance, and knockdown patterns in Anopheles gambiae sensu lato in areas with and areas without insecticide resistance in Teso North and Teso South subcounties, Western Kenya. Materials and Methods. For WHO vulnerability tests, mosquito larvae were sampled using a dipper, reared into 3-5-day-old female mosquitoes (4944 at 100 mosquitoes per insecticide) which were exposed to 0.75% permethrin, 0.05% deltamethrin, and 0.1% bendiocarb using the WHO tube assay method. Species identification and kdr East gene PCRs were also performed on randomly selected mosquitoes from the collections; including adult mosquitoes (3448) sampled using standard collection methods. Results. Anopheles gambiae sensu stricto were the majority in terms of species composition at 78.9%. Bendiocarb caused 100% mortality while deltamethrin had higher insecticidal effects (77%) on female mosquitoes than permethrin (71%). Susceptible Kengatunyi cluster had higher proportion of An. arabiensis (20.9%) than resistant Rwatama (10.7%). Kengatunyi mosquitoes exposed to deltamethrin had the highest KDT50 R of 8.2. Both Anopheles gambiae sensu stricto and Anopheles arabiensis had equal S allelic frequency of 0.84. Indoor resting mosquitoes had 100% mortality rate after 24 h since exposure. Overall SS genotypic frequency in Teso North and Teso South subcounties was 79.4% against 13.7% homozygous LL genotype and 6.9% heterozygous LS genotype. There was a significant difference (ρ<0.05) in S allele frequencies between Kengatunyi (0.61) and Rwatama (0.95). Mosquito samples collected in 2013 had the highest S allelic frequency of 0.87. Discussion. Most likely, the higher the selection pressure exerted indoors by insecticidal nets, the higher were the resistance alleles. Use of pyrethroid impregnated nets and agrochemicals may have caused female mosquitoes to select for pyrethroid resistance. Different modes of action and chemical properties in different types of pyrethroids aggravated by a variety of edaphic and climatic factors may have caused different levels of susceptibility in both indoor and outdoor vectors to pyrethroids and carbamate. Species composition and populations in each collection method may have been influenced by insecticide resistance capacity in different species. Conclusions and Recommendations. Both phenotypic and genotypic insecticide resistance levels have been confirmed in Teso North and Teso South subcounties in Western Kenya. Insecticide resistance management practices in Kenya should be fast tracked and harmonized with agricultural sector agrochemical-based activities and legislation, and possibly switch to carbamate use in order to ease selection pressure on pyrethroids which are useable in insecticidal nets and indoor residual spray due to their low human toxicity. The implication of such high resistance levels in mosquitoes collected in Teso subcounties is that resistance is likely to persist and or even increase if monomolecules of permethrin and deltamethrin or both continue to be used in all net- and nonnet-based mosquito control purposes. Usage of mutually reinforcing piperonyl butoxide (PBO) that prohibits particular enzymes vital in metabolic activities inside mosquito systems and has been integrated into pyrethroid-LLINs to create pyrethroid-PBO nets is an extremely viable option.

scholarly journals Impact of Insecticide Resistance on P. falciparum Vectors’ Biting, Feeding, and Resting Behaviour in Selected Clusters in Teso North and South Subcounties in Busia County, Western Kenya

2020 ◽  
Vol 2020 ◽  
pp. 1-11
Author(s):  
Edward K. Githinji ◽  
Lucy W. Irungu ◽  
Paul N. Ndegwa ◽  
Maxwell G. Machani ◽  
Richard O. Amito ◽  
...  
Keyword(s):  
Insecticide Resistance ◽  
Human Blood ◽  
World Health ◽  
Assay Method ◽  
Genotypic Frequency ◽  
Western Kenya ◽  
Resting Behaviour ◽  
Significant Difference ◽  
Homozygous Resistant ◽  
The Impact

Introduction. Behavioural resistance to insecticides restrains the efficacy of vector control tools against mosquito-transmitted diseases. The current study is aimed at determining the impact of insecticide resistance on major malaria vectors’ biting, feeding, and resting behaviour in areas with and areas without insecticide resistance in Teso North and Teso South, Busia County, Western Kenya. Methods. Mosquito larvae were sampled using a dipper, reared into 3-5-day-old female mosquitoes [4944] which were exposed to 0.75% permethrin and 0.05% deltamethrin using World Health Organization tube assay method. Blood meal, species identification, and kdr Eastgene PCRs were also performed on adult mosquitoes sampled using mosquito collection methods [3448]. Biting, feeding, resting, and exiting behaviours of field-collected mosquitoes from five selected clusters were analysed. Results. The lowest Kdr genotypic frequency (SS) proportion was found in female Anophelines collected in Kengatunyi at 58% while Rwatama had the highest genotypic frequency at 93%, thus susceptible and resistant clusters, respectively. The peak hour for mosquito seeking a human bite was between 0300 and 0400 hrs in the resistant cluster and 0400-0500 hrs in the susceptible cluster. The heterozygous mosquitoes maintained the known 2100-2200 hrs peak hour. There was a higher proportion of homozygous susceptible vectors (86.4%) seeking humans indoor than outdoor bitters (78.3%). Mosquito blood meals of human origin were 60% and 87% in susceptible Kengatunyi and resistant Rwatama cluster, respectively. There was significant difference between homozygous-resistant vectors feeding on human blood compared to homozygous susceptible mosquitoes (p≤0.05). The proportion of bovine blood was highest in the susceptible cluster. A higher proportion of homozygous-resistant anophelines were feeding and resting indoors. No heterozygous mosquito was found resting indoor while 4.2% of the mosquitoes were caught while exiting the house through the window. Discussion. A shift in resistant Anopheles gambiae sl highest peak hour of aggressiveness from 2100-2200 hrs to 0300-0400 hrs is a key change in its biting pattern. Due to the development of resistance, mosquitoes no longer have to compete against the time the human host enters into the formerly lethal chemical and or physical barrier in the form of long-lasting insecticide-treated net. No heterozygous LS mosquito rested indoors possibly due to disadvantages of heterozygosity which could have increased their fitness costs as well as energy costs in the presence of the insecticidal agents in the treated nets. Conclusions and recommendations. Out of bed biting by female mosquitoes and partial susceptibility may contribute to residual malaria transmission. Insecticide-resistant vectors have become more endophagic and anthropophillic. Hence, insecticidal nets, zooprophylaxis, and novel repellents are still useful chemical, biological, and physical barriers against human blood questing female mosquitoes. Further studies should be done on genetic changes in mosquitoes and their effects on changing mosquito behaviour.

scholarly journals Phenotypic, genotypic and biochemical changes during pyrethroid resistance selection in Anopheles gambiae mosquitoes

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Maxwell G. Machani ◽  
Eric Ochomo ◽  
Daibin Zhong ◽  
Guofa Zhou ◽  
Xiaoming Wang ◽  
...  
Keyword(s):  
Public Health ◽  
Insecticide Resistance ◽  
Anopheles Gambiae ◽  
Selection Pressure ◽  
Pyrethroid Resistance ◽  
Natural Populations ◽  
Biochemical Changes ◽  
Moderate Intensity ◽  
Agricultural System ◽  
Selection For

Abstract The directional selection for insecticide resistance due to indiscriminate use of insecticides in public health and agricultural system favors an increase in the frequency of insecticide-resistant alleles in the natural populations. Similarly, removal of selection pressure generally leads to decay in resistance. Past investigations on the emergence of insecticide resistance in mosquitoes mostly relied on field survey of resistance in vector populations that typically had a complex history of exposure to various public health and agricultural pest control insecticides in nature, and thus the effect of specific insecticides on rate of resistance emergency or resistance decay rate is not known. This study examined the phenotypic, genotypic, and biochemical changes that had occurred during the process of selection for pyrethroid resistance in Anopheles gambiae, the most important malaria vector in Africa. In parallel, we also examined these changes in resistant populations when there is no selection pressure applied. Through repeated deltamethrin selection in adult mosquitoes from a field population collected in western Kenya for 12 generations, we obtained three independent and highly pyrethroid-resistant An. gambiae populations. Three susceptible populations from the same parental population were generated by removing selection pressure. These two lines of mosquito populations differed significantly in monooxygenase and beta-esterase activities, but not in Vgsc gene mutation frequency, suggesting metabolic detoxification mechanism plays a major role in generating moderate-intensity resistance or high-intensity resistance. Pre-exposure to the synergist piperonyl butoxide restored the susceptibility to insecticide among the highly resistant mosquitoes, confirming the role of monooxygenases in pyrethroid resistance. The rate of resistance decay to become fully susceptible from moderate-intensity resistance took 15 generations, supporting at least 2-years interval is needed when the rotational use of insecticides with different modes of action is considered for resistance management.

scholarly journals Anopheles gambiae and Anopheles arabiensis population densities and infectivity in Kopere village, Western Kenya

2012 ◽  
Vol 6 (08) ◽  
pp. 637-643 ◽  
Author(s):  
Andrew Ambogo Obala ◽  
Helen L Kutima ◽  
Henry D.N. Nyamogoba ◽  
Anne W Mwangi ◽  
Chrispinus J Simiyu ◽  
...  
Keyword(s):  
Anopheles Gambiae ◽  
Malaria Vector ◽  
Anopheles Arabiensis ◽  
Mosquito Species ◽  
Sensu Stricto ◽  
Malaria Vector Control ◽  
Insecticide Treated Nets ◽  
Western Kenya ◽  
Endemic Malaria ◽  
Vector Mosquito

Introduction: This study was conducted in a sugar belt region of western Kenya interfacing epidemic and endemic malaria transmission. We investigated Anopheles gambiae sensu stricto (ss) and Anopheles arabiensis species compositions and densities, human host choice, and infectivity. Methodology: Mosquitoes were captured using pyrethrum spray catch technique and first identified based on morphology; species were confirmed by PCR. Blood meal preference and sporozoite rates were determined by ELISA. Parity rates and entomological inoculation rates (EIR) were determined. Seasonal densities were compared against environmental temperatures, relative humidity and rainfall. Results: In total 2,426 An. gambiae were collected.  Out of 1,687 female blood-fed mosquitoes, 272 were randomly selected for entomological tests. An. gambiae ss and An. arabiensis comprised 75% (205/272) and 25% (68/272) of the selection, respectively. An. gambiae ss had higher preference for human blood (97%; n=263/272) compared with An. arabiensis, which mostly fed on bovines (88%; n=239/272).  The sporozoite and parity rates were 6% (16/272) and 66% (179/272) for An. gambiae ss and 2% (4/272) and 53% (144/272) for An. arabiensis respectively, while EIR was 0.78 infective bites/person/night.  Climate (ANOVA; F=14.2; DF=23) and temperature alone (r=0.626; t=3.75; p=0.001) were significantly correlated with vector densities. Conclusion: An. gambiae ss are the most efficient malaria vector mosquito species in Kopere village. Because An. gambiae ss largely rests and feeds indoors, use of indoor residual spray and insecticide-treated nets is likely the most suitable approach to malaria vector control in Kopere village and other parts of Kenya where this species is abundant. 

scholarly journals Repellency and Composition of Essential Oils of Selected Ethnobotanical Plants Used in Western Kenya against Bites of Anopheles gambiae Sensu Stricto

2020 ◽  
Vol 23 (3) ◽  
pp. 432-441
Author(s):  
David O. Ywaya ◽  
Michael A. Birkett ◽  
John A. Pickett ◽  
John B. Ochola ◽  
Lwande Wilber ◽  
...  
Keyword(s):  
Essential Oils ◽  
Anopheles Gambiae ◽  
Sensu Stricto ◽  
Western Kenya ◽  
Anopheles Gambiae Sensu Stricto

scholarly journals Molecular Characterization and Genotype Distribution of Thioester-containing Protein 1 Gene, A Key Regulator of Malaria Transmission in An. Gambiae Mosquitoes in Western Kenya

2021 ◽  
Author(s):  
Shirley A. Onyango ◽  
Kevin O. Ochwedo ◽  
Maxwell G. Machani ◽  
Collince J. Omondi ◽  
Isaiah Debrah ◽  
...  
Keyword(s):  
Population Structure ◽  
Anopheles Gambiae ◽  
Malaria Transmission ◽  
Mosquito Species ◽  
Malaria Vectors ◽  
Fixation Index ◽  
Genotype Distribution ◽  
Low Frequencies ◽  
Western Kenya ◽  
Significant Difference

Abstract BackgroundEvolutionary pressures lead to the selection of efficient malaria vectors either resistant or susceptible to Plasmodiumparasites.These forcesmay elevate the introduction of new species genotypes that adapt to new breeding habitats which could have serious implications on malaria transmission.Thioester-containing protein 1 (TEP1) of Anopheles gambiaeplays an important role in innate immune defenses against parasites. This study aims to characterize the distribution pattern of TEP1 polymorphisms determining vector competence and subsequently malaria transmission in western Kenya. MethodsAnopheles gambiaeadult and larvae were collected using pyrethrum spray catches (PSC) and plastic dippers respectivelyfrom Homa Bay, Kakamega, Bungoma, and Kisumu countiesbetween 2017 and 2020.Collected adults and larvae reared to the adult stage were morphologically identified and then identified to sibling species by PCR.TEP1 alleles were determined using restriction fragment length polymorphisms-polymerase chain reaction (RFLP-PCR) and to validate the TEP1 genotyping results, a representative sample of alleles was sequenced.ResultsTwo TEP1 alleles (TEP1*S1 and TEP1*R2)and three corresponding genotypes (*S1/S1, *R2/S1, and *R2/R2)were identified. TEP1*S1 and TEP1*R2 with their corresponding genotypes, homozygous *S1/S1 and heterozygous *R2/S1 were widely distributed across all sites with allele frequencies of approximately 80% and 20%, respectively bothin An. gambiaeand An. arabiensis. There was no significant difference detected among the population and between the two mosquito species in TEP1 allele frequency and genotype frequency. The overall low levels in population structure (FST= 0.019) across all sites corresponded to an effective migration index (Nm= 12.571) and lowNei’s genetic distance values (<0.500) among the subpopulation.The comparative fixation index values revealed minimal genetic differentiation between speciesand high levels of gene flow among populations.ConclusionThere is a low genetic diversity and population structure in western Kenya. TEP1* R2 and TEP1*S1 were the most common alleles in both species which may have been maintained through generations in time, However, the TEP1*R2 allele was in low frequencies and may be used to estimatemalaria prevalence. Continued surveillance of the distribution of TEP1 is essential for monitoring the population dynamics of local vectors and their implications on malaria transmission and hence designing targeted vector interventions.

scholarly journals First Report of Target Site Insensitivity in Pyrethroid Resistant Anopheles gambiae from Southern Guinea Savanna, Northern-Nigeria

2020 ◽  
Author(s):  
Mustapha Ahmed-Yusuf ◽  
Hassan Vatandoost ◽  
Mohammad Ali Oshaghi ◽  
Ahmad Ali Hanafi-Bojd ◽  
Ahmad Ali Enayati ◽  
...  
Keyword(s):  
Anopheles Gambiae ◽  
Public Health Problem ◽  
Allelic Frequency ◽  
Target Site ◽  
Major Public Health Problem ◽  
Genotypic Frequency ◽  
Northern Nigeria ◽  
Guinea Savanna ◽  
L1014f Kdr ◽  
Anopheles Gambiae S.L

Background: Malaria is a major public health problem and life threatening parasitic vector-borne disease. For the first time, we established and report the molecular mechanism responsible for Anopheles gambiae s.l. resistance to pyrethroids and DDT from Yamaltu Deba, Southern Guinea Savanna, Northern-Nigeria. Methods: The susceptibility profile of An. gambiae s.l. to four insecticides (DDT 4%, bendiocarb 0.1%, malathion 5% and deltamethrin 0.05%) using 2–3 days old females from larvae collected from study area between August and November, 2018 was first established. Genomic DNA was then extracted from 318 mosquitoes using Livak DNA extraction protocol for specie identification and kdr genotyping. The mosquitoes were identified to species level and then 96 genotyped for L1014F and L1014S kdr target site mutations. Results: The mosquitoes were all resistant to DDT, bendiocarb and deltamethrin but fully susceptible to malathion. An. coluzzii was found to be the dominant sibling species (97.8%) followed by An. arabiensis (1.9%) and An. gambiae s.s (0.3%). The frequency of the L1014F kdr mutation was relatively higher (83.3%) than the L1014S (39%) in the threespecies studied. The L1014F showed a genotypic frequency of 75% resistance (RR), 17% heterozygous (RS) and 8% susceptible (SS) with an allelic frequency of 87% RR and 13% SS while the L1014S showed a genotypic frequency of RR (16%), RS (38%) and SS (46%) with an allelic frequency of 40% RR and 60% SS, respectively. Conclusion: This study reveals that both kdr mutations present simultaneously in Northern-Nigeria, however contribution of L1014F which is common in West Africa was more than twice of L1014S mutation found in East Africa.

scholarly journals Anopheles gambiae sensu stricto Aquatic Stages Development Comparison between Insectary and Semifield Structure

2015 ◽  
Vol 2015 ◽  
pp. 1-6
Author(s):  
Eliningaya J. Kweka ◽  
Filemoni Tenu ◽  
Frank Magogo ◽  
Leonard E. G. Mboera
Keyword(s):  
Anopheles Gambiae ◽  
Malaria Vector ◽  
Adult Emergence ◽  
Sensu Stricto ◽  
Malaria Vector Control ◽  
Clear Understanding ◽  
Fish Food ◽  
Anopheles Gambiae Sensu Stricto ◽  
Significant Difference ◽  
Larvae Development

Effective malaria vector control initiatives need a clear understanding of mosquito behaviour and its ecology. This study compared larvae development to adult emergence in insectary and malaria-sphere (SFS). This is the preliminary study which gives an insight to forthcoming studies. Anopheles gambiae sensu stricto eggs were hatched in insectary and transferred in densities of 20 and 50 per microhabitat with twenty replicates of each density. Both densities of larvae were reared in semifield structure and in insectary from the same batch of eggs. They were provided with tetramin fish food. In both densities of 20 and 50, pupation rate and time were found to be similar in SFS and insectary, but, in survivorship from larvae to pupae at density of 50, more larvae survived significantly to pupae stage in SFS than in insectary (P=0.002). The adult emergence rates were similar for densities of 20 and 50 between SFS and Insectary. There was a significant difference between SFS and insectary in light intensity (P=0.001) and temperatures (P=0.001), with SFS having higher rates than insectary. The findings of this study have shown that larvae development rates are encouraging having semifield structures for malaria vector rearing for behavioural studies toward malaria control.

scholarly journals Species composition and insecticide resistance status of Anopheles gambiae (s.l.) (Culicidae) in Kome, southern Chad and the implications for malaria control

2016 ◽  
Vol 9 (1) ◽  
Author(s):  
Samuel Dadzie ◽  
Maxwell A. Appawu ◽  
Clement Kerah-Hinzoumbe ◽  
Martin C. Akogbeto ◽  
Michele Adimazoya ◽  
...  
Keyword(s):  
Species Composition ◽  
Insecticide Resistance ◽  
Anopheles Gambiae ◽  
Malaria Control ◽  
Anopheles Gambiae S.L

scholarly journals Western Kenyan Anopheles gambiae showing intense permethrin resistance harbour distinct microbiota

2021 ◽  
Vol 20 (1) ◽  
Author(s):  
Diana Omoke ◽  
Mathew Kipsum ◽  
Samson Otieno ◽  
Edward Esalimba ◽  
Mili Sheth ◽  
...  
Keyword(s):  
Insecticide Resistance ◽  
Anopheles Gambiae ◽  
High Throughput Sequencing ◽  
Pyrethroid Resistance ◽  
Sensu Stricto ◽  
Malaria Vector Control ◽  
Rrna Gene ◽  
Vector Surveillance ◽  
Bacterial Composition ◽  
Microbial Analysis

Abstract Background Insecticide resistance poses a growing challenge to malaria vector control in Kenya and around the world. Following evidence of associations between the mosquito microbiota and insecticide resistance, the microbiota of Anopheles gambiae sensu stricto (s.s.) from Tulukuyi village, Bungoma, Kenya, with differing permethrin resistance profiles were comparatively characterized. Methods Using the CDC bottle bioassay, 133 2–3 day-old, virgin, non-blood fed female F1 progeny of field-caught An. gambiae s.s. were exposed to five times (107.5 µg/ml) the discriminating dose of permethrin. Post bioassay, 50 resistant and 50 susceptible mosquitoes were subsequently screened for kdr East and West mutations, and individually processed for microbial analysis using high throughput sequencing targeting the universal bacterial and archaeal 16S rRNA gene. Results 47 % of the samples tested (n = 133) were resistant, and of the 100 selected for further processing, 99 % were positive for kdr East and 1 % for kdr West. Overall, 84 bacterial taxa were detected across all mosquito samples, with 36 of these shared between resistant and susceptible mosquitoes. A total of 20 bacterial taxa were unique to the resistant mosquitoes and 28 were unique to the susceptible mosquitoes. There were significant differences in bacterial composition between resistant and susceptible individuals (PERMANOVA, pseudo-F = 2.33, P = 0.001), with presence of Sphingobacterium, Lysinibacillus and Streptococcus (all known pyrethroid-degrading taxa), and the radiotolerant Rubrobacter, being significantly associated with resistant mosquitoes. On the other hand, the presence of Myxococcus, was significantly associated with susceptible mosquitoes. Conclusions This is the first report of distinct microbiota in An. gambiae s.s. associated with intense pyrethroid resistance. The findings highlight differentially abundant bacterial taxa between resistant and susceptible mosquitoes, and further suggest a microbe-mediated mechanism of insecticide resistance in mosquitoes. These results also indicate fixation of the kdr East mutation in this mosquito population, precluding further analysis of its associations with the mosquito microbiota, but presenting the hypothesis that any microbe-mediated mechanism of insecticide resistance would be likely of a metabolic nature. Overall, this study lays initial groundwork for understanding microbe-mediated mechanisms of insecticide resistance in African mosquito vectors of malaria, and potentially identifying novel microbial markers of insecticide resistance that could supplement existing vector surveillance tools.

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