Last data update: Nov 04, 2024. (Total: 48056 publications since 2009)
Records 1-30 (of 96 Records) |
Query Trace: Lenhart A[original query] |
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Locally acquired (autochthonous) mosquito-transmitted plasmodium vivax malaria - Saline County, Arkansas, September 2023
Courtney AP , Boyanton BL Jr , Strebeck PV , Blount K , Ledford S , Ridpath AD , Mace KE , Smith C , Garner K , Waters C , Cima MJ , Patil N , McElroy PD , Raphael BH , Sapp SGH , Qvarnstrom Y , Lenhart A , Sutcliffe A , Dulski TM , Rothfeldt L . MMWR Morb Mortal Wkly Rep 2024 73 (42) 646-649 A case of locally acquired (autochthonous) mosquito-transmitted Plasmodium vivax malaria was diagnosed in Arkansas in September 2023. This represents the 10th autochthonous case identified nationally in 2023, after 20 years without recorded local mosquitoborne malaria transmission in the United States. The public health response included case investigation, active case surveillance, mosquito surveillance and control, assessment of medical countermeasures, and clinical and public outreach. Prompt diagnosis and appropriate treatment of malaria can improve clinical outcomes and, in addition to vector control, minimize risk for local transmission. Clinicians should consider malaria among patients who have traveled to countries where malaria is endemic, or with unexplained fever regardless of travel history. Although the risk for autochthonous malaria in the United States remains very low, its reemergence highlights the importance of vectorborne disease preparedness and response. Examples of such efforts include improving awareness among clinicians, access to diagnostics and antimalarial medications, and capacity for mosquito surveillance and control. Collaboration and communication among CDC, health departments, local jurisdictions, clinicians, hospitals, laboratories, and the public can support rapid malaria diagnosis, prevention, and control. Before traveling internationally to areas where malaria is endemic, travelers should consult with their health care provider regarding recommended malaria prevention measures, including chemoprophylaxis and precautions to avoid mosquito bites, to reduce both personal and community risk. |
The TIRS trial: Enrollment procedures and baseline characterization of a pediatric cohort to quantify the epidemiologic impact of targeted indoor residual spraying on Aedes-borne viruses in Merida, Mexico
Earnest JT , Kirstein OD , Mendoza AC , Barrera-Fuentes GA , Puerta-Guardo H , Parra-Cardeña M , Yam-Trujillo K , Collins MH , Pavia-Ruz N , Ayora-Talavera G , Gonzalez-Olvera G , Medina-Barreiro A , Bibiano-Marin W , Lenhart A , Halloran ME , Longini I , Dean N , Waller LA , Crisp AM , Correa-Morales F , Palacio-Vargas J , Granja-Perez P , Villanueva S , Delfın-Gonzalez H , Gomez-Dantes H , Manrique-Saide P , Vazquez-Prokopec GM . PLoS One 2024 19 (9) e0310480 Aedes mosquito-borne viruses (ABVs) place a substantial strain on public health resources in the Americas. Vector control of Aedes mosquitoes is an important public health strategy to decrease or prevent spread of ABVs. The ongoing Targeted Indoor Residual Spraying (TIRS) trial is an NIH-sponsored clinical trial to study the efficacy of a novel, proactive vector control technique to prevent dengue virus (DENV), Zika virus (ZIKV), and chikungunya virus (CHIKV) infections in the endemic city of Merida, Yucatan, Mexico. The primary outcome of the trial is laboratory-confirmed ABV infections in neighborhood clusters. Despite the difficulties caused by the COVID-19 pandemic, by early 2021 the TIRS trial completed enrollment of 4,792 children aged 2-15 years in 50 neighborhood clusters which were allocated to control or intervention arms via a covariate-constrained randomization algorithm. Here, we describe the makeup and ABV seroprevalence of participants and mosquito population characteristics in both arms before TIRS administration. Baseline surveys showed similar distribution of age, sex, and socio-economic factors between the arms. Serum samples from 1,399 children were tested by commercially available ELISAs for presence of anti-ABV antibodies. We found that 45.1% of children were seropositive for one or more flaviviruses and 24.0% were seropositive for CHIKV. Of the flavivirus-positive participants, most were positive for ZIKV-neutralizing antibodies by focus reduction neutralization testing which indicated a higher proportion of participants with previous ZIKV than DENV infections within the cohort. Both study arms had statistically similar seroprevalence for all viruses tested, similar socio-demographic compositions, similar levels of Ae. aegypti infestation, and similar observed mosquito susceptibility to insecticides. These findings describe a population with a high rate of previous exposure to ZIKV and lower titers of neutralizing antibodies against DENV serotypes, suggesting susceptibility to future outbreaks of flaviviruses is possible, but proactive vector control may mitigate these risks. |
Widespread geographic distribution of Aedes aegypti (Diptera: Culicidae) kdr variants in Panama
García J , Chong M , Rojas AL , McMillan WO , Bennett KL , Lenhart AE , Chaves LF , Loaiza JR . J Med Entomol 2024 We searched for evidence of knockdown resistance (kdr) mutations in the voltage-gated sodium channel gene of Aedes aegypti (Linnaeus) (Diptera: Culicidae) and Aedes albopictus (Skuse) (Diptera: Culicidae) mosquitoes from Panama. Conventional PCR was performed on 469 Ae. aegypti and 349 Ae. albopictus. We did not discover kdr mutations in Ae. albopictus, but 2 nonsynonymous kdr mutations, V1016I (found in 101 mosquitoes) and F1534C (found in 29 of the mosquitoes with the V1016I), were detected in Ae. aegypti. These kdr mutations were present in all specimens that were successfully sequenced for both IIS5-S6 and IIIS6 regions, which included samples collected from 8 of the 10 provinces of Panama. No other kdr mutations were found in Ae. aegypti, including V1016G, which has already been reported in Panama. Findings suggest that the V1016I-F1534C variant is prevalent in Panama, which might be related to the introduction and passive movement of mosquitoes as part of the used-tire trade. However, we cannot rule out the possibility that selection on de novo replacement of kdr mutations also partially explains the widespread distribution pattern of these mutations. These 2 ecological and evolutionary processes are not mutually exclusive, though, as they can occur in tandem. Research in Panama needs to calculate the genotypic and allelic frequencies of kdr alleles in local Ae. aegypti populations and to test whether some combinations confer phenotypic resistance or not. Finally, future studies will have to track the introduction and spreading of new kdr mutations in both Aedes species. |
Key gene modules and hub genes associated with pyrethroid and organophosphate resistance in Anopheles mosquitoes: a systems biology approach
Odhiambo CA , Derilus D , Impoinvil LM , Omoke D , Saizonou H , Okeyo S , Dada N , Mulder N , Nyamai D , Nyanjom S , Lenhart A , Djogbénou LS , Ochomo E . BMC Genomics 2024 25 (1) 665 Indoor residual spraying (IRS) and insecticide-treated nets (ITNs) are the main methods used to control mosquito populations for malaria prevention. The efficacy of these strategies is threatened by the spread of insecticide resistance (IR), limiting the success of malaria control. Studies of the genetic evolution leading to insecticide resistance could enable the identification of molecular markers that can be used for IR surveillance and an improved understanding of the molecular mechanisms associated with IR. This study used a weighted gene co-expression network analysis (WGCNA) algorithm, a systems biology approach, to identify genes with similar co-expression patterns (modules) and hub genes that are potential molecular markers for insecticide resistance surveillance in Kenya and Benin. A total of 20 and 26 gene co-expression modules were identified via average linkage hierarchical clustering from Anopheles arabiensis and An. gambiae, respectively, and hub genes (highly connected genes) were identified within each module. Three specific genes stood out: serine protease, E3 ubiquitin-protein ligase, and cuticular proteins, which were top hub genes in both species and could serve as potential markers and targets for monitoring IR in these malaria vectors. In addition to the identified markers, we explored molecular mechanisms using enrichment maps that revealed a complex process involving multiple steps, from odorant binding and neuronal signaling to cellular responses, immune modulation, cellular metabolism, and gene regulation. Incorporation of these dynamics into the development of new insecticides and the tracking of insecticide resistance could improve the sustainable and cost-effective deployment of interventions. |
Insecticide susceptibility status of Anopheles albimanus populations in historical malaria foci in Quintana Roo, Mexico
Escobar D , González-Olvera G , Gómez-Rivera Á S , Navarrete-Carballo J , Mis-Ávila P , Baack-Valle R , Escalante G , Reyes-Cabrera G , Correa-Morales F , Che-Mendoza A , Vazquez-Prokopec G , Lenhart A , Manrique-Saide P . Malar J 2024 23 (1) 165 BACKGROUND: Mexico has experienced a significant reduction in malaria cases over the past two decades. Certification of localities as malaria-free areas (MFAs) has been proposed as a steppingstone before elimination is achieved throughout the country. The Mexican state of Quintana Roo is a candidate for MFA certification. Monitoring the status of insecticide susceptibility of major vectors is crucial for MFA certification. This study describes the susceptibility status of Anopheles albimanus, main malaria vector, from historically important malaria foci in Quintana Roo, using both phenotypic and genotypic approaches. METHODS: Adult mosquito collections were carried out at three localities: Palmar (Municipality of Othon P. Blanco), Buenavista (Bacalar) and Puerto Morelos (Puerto Morelos). Outdoor human-landing catches were performed by pairs of trained staff from 18:00 to 22:00 during 3-night periods at each locality during the rainy season of 2022. Wild-caught female mosquitoes were exposed to diagnostic doses of deltamethrin, permethrin, malathion, pirimiphos-methyl or bendiocarb using CDC bottle bioassays. Mortality was registered at the diagnostic time and recovery was assessed 24 h after exposure. Molecular analyses targeting the Voltage-Gated Sodium Channel (vgsc) gene and acetylcholinesterase (ace-1) gene were used to screen for target site polymorphisms. An SNP analysis was carried out to identify mutations at position 995 in the vgsc gene and at position 280 in the ace-1 gene. RESULTS: A total of 2828 anophelines were collected. The main species identified were Anopheles albimanus (82%) and Anopheles vestitipennis (16%). Mortalities in the CDC bottle bioassay ranged from 99% to 100% for all the insecticides and mosquito species. Sequence analysis was performed on 35 An. albimanus across the three localities; of those, 25 were analysed for vgsc and 10 for ace-1 mutations. All individuals showed wild type alleles. CONCLUSION: The results demonstrated that An. albimanus populations from historical malaria foci in Quintana Roo are susceptible to the main insecticides used by the Ministry of Health. |
Chemical control of medically important arthropods in Panama: A systematic literature review of historical efforts
Tuñon A , García J , Carrera LC , Chaves LF , Lenhart AE , Loaiza JR . Acta Trop 2024 107217 Vector-borne diseases are a major source of morbidity in Panama. Herein, we describe historical usage patterns of synthetic insecticides to control arthropod disease vectors in this country. We examine the influence of interventions by vector control programs on the emergence of insecticide resistance. Chemical control has traditionally focused on two mosquito species: Anopheles albimanus, a major regional malaria vector, and Aedes aegypti, a historical vector of yellow fever, and current vector of dengue, chikungunya, and Zika. Countrywide populations of An. albimanus depict hyperirritability to organochlorine insecticides administered by indoor residual spraying, although they appear susceptible to these insecticides in bioassays settings, as well as to organophosphate and carbamate insecticides in field tests. Populations of Ae. aegypti show resistance to pyrethroids, particularly in areas near Panama City, but the spread of resistance remains unknown in Ae. aegypti and Aedes albopictus. A One Health approach is needed in Panama to pinpoint the insecticide resistance mechanisms including the frequency of knockdown mutations and behavioral plasticity in populations of Anopheles and Aedes mosquitoes. This information is necessary to guide the sustainable implementation of chemical control strategies and the use of modern vector control technologies such as genetically modified mosquitoes, and endosymbiont Wolbachia-based biological control. |
Physical durability and insecticidal activity of long-lasting insecticidal nets in Cruzeiro do Sul, Brazil
Feio-Dos-Santos AC , Reis CC , Sucupira IMC , Lenhart A , Santos MMM , Reis ER , do Carmo EL , Daniel S , Mesones Lapouble OM , de Oliveira AM , Povoa MM . Sci Rep 2024 14 (1) 9044 Vector control is one of the principal strategies used for reducing malaria transmission. Long-lasting insecticidal bed nets (LLINs) are a key tool used to protect populations at risk of malaria, since they provide both physical and chemical barriers to prevent human-vector contact. This study aimed to assess the physical durability and insecticidal efficacy of LLINs distributed in Cruzeiro do Sul (CZS), Brazil, after 4 years of use. A total of 3000 LLINs (PermaNet 2.0) were distributed in high malaria risk areas of CZS in 2007. After 4 years of use, 27 'rectangular' LLINs and 28 'conical' LLINs were randomly selected for analysis. The evaluation of physical integrity was based on counting the number of holes and measuring their size and location on the nets. Insecticidal efficacy was evaluated by cone bioassays, and the amount of residual insecticide remaining on the surface of the LLINs was estimated using a colorimetric method. After 4 years of use, physical damage was highly prevalent on the rectangular LLINs, with a total of 473 holes detected across the 27 nets. The upper portion of the side panels sustained the greatest damage in rectangular LLINs. The overall mosquito mortality by cone bioassay was < 80% in 25/27 rectangular LLINs, with panel A (at the end of the rectangular bednet) presenting the highest mortality (54%). The overall mean insecticide concentration was 0.5 µg/sample, with the bednet roof containing the highest average concentration (0.61 µg/sample). On the conical LLINs, 547 holes were detected, with the bottom areas sustaining the greatest damage. The cone bioassay mortality was < 80% in 26/28 of the conical LLINs. The mean insecticide concentration was 0.3 µg/sample. After 4 years of use, the insecticidal efficacy of the LLINs was diminished to below acceptable thresholds. |
Transcriptomic analysis of Anopheles gambiae from Benin reveals overexpression of salivary and cuticular proteins associated with cross-resistance to pyrethroids and organophosphates
Saizonou H , Impoinvil LM , Derilus D , Omoke D , Okeyo S , Dada N , Corredor C , Mulder N , Lenhart A , Ochomo E , Djogbénou LS . BMC Genomics 2024 25 (1) 348 BACKGROUND: Insecticide 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). RESULTS: Larvae 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. CONCLUSION: Our 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. |
Whole transcriptomic analysis reveals overexpression of salivary gland and cuticular proteins genes in insecticide-resistant Anopheles arabiensis from Western Kenya
Omoke D , Impoinvil LM , Derilus D , Okeyo S , Saizonou H , Mulder N , Dada N , Lenhart A , Djogbénou L , Ochomo E . BMC Genomics 2024 25 (1) 313 BACKGROUND: Effective vector control is key to malaria prevention. However, this is now compromised by increased insecticide resistance due to continued reliance on insecticide-based control interventions. In Kenya, we have observed heterogenous resistance to pyrethroids and organophosphates in Anopheles arabiensis which is one of the most widespread malaria vectors in the country. We investigated the gene expression profiles of insecticide resistant An. arabiensis populations from Migori and Siaya counties in Western Kenya using RNA-Sequencing. Centers for Disease Control and Prevention (CDC) bottle assays were conducted using deltamethrin (DELTA), alphacypermethrin (ACYP) and pirimiphos-methyl (PMM) to determine the resistance status in both sites. RESULTS: Mosquitoes from Migori had average mortalities of 91%, 92% and 58% while those from Siaya had 85%, 86%, and 30% when exposed to DELTA, ACYP and PMM, respectively. RNA-Seq analysis was done on pools of mosquitoes which survived exposure ('resistant'), mosquitoes that were not exposed, and the insecticide-susceptible An. arabiensis Dongola strain. Gene expression profiles of resistant mosquitoes from both Migori and Siaya showed an overexpression mainly of salivary gland proteins belonging to both the short and long form D7 genes, and cuticular proteins (including CPR9, CPR10, CPR15, CPR16). Additionally, the overexpression of detoxification genes including cytochrome P450s (CYP9M1, CYP325H1, CYP4C27, CYP9L1 and CYP307A1), 2 carboxylesterases and a glutathione-S-transferase (GSTE4) were also shared between DELTA, ACYP, and PMM survivors, pointing to potential contribution to cross resistance to both pyrethroid and organophosphate insecticides. CONCLUSION: This study provides novel insights into the molecular basis of insecticide resistance in An. arabiensis in Western Kenya and suggests that salivary gland proteins and cuticular proteins are associated with resistance to multiple classes of insecticides. |
Postintervention immunological and entomological survey of lymphatic filariasis in the City of Olinda, Brazil, 2015-2016
Ramesh A , Oliveira P , Cameron M , Castanha PMS , Walker T , Lenhart A , Impoinvil L , Alexander N , Medeiros Z , Sá A , Rocha A , Souza WV , Maciel A , Braga C . Am J Trop Med Hyg 2024 Lymphatic filariasis (LF) is a leading cause of disability due to infectious disease worldwide. The Recife Metropolitan Region (RMR) is the only remaining focus of LF in Brazil, where the parasite Wuchereria bancrofti is transmitted solely by the mosquito Culex quinquefasciatus. This study reports the results of transmission assessment surveys and molecular xenomonitoring in the city of Olinda, RMR, after nearly 15 years (2015-2016) of interventions for LF elimination. Participants were screened for W. bancrofti antigen via immunochromatographic card tests (ICT) in: 1) door-to-door surveys conducted for all children aged 5-7 years from 4 out of 17 intervention areas treated with at least five annual doses of mass drug administration (MDA), and 2) a two-stage cluster sampling survey of residents aged 5 years and older in non-MDA areas. Mosquitoes were collected via handheld aspirators in four MDA areas, differentiated by species, sex, and physiological status, pooled into groups of up to 10 blood-fed, semigravid, and gravid mosquitoes, and screened for W. bancrofti infection by real-time quantitative polymerase chain reaction (RT-qPCR). All 1,170 children from MDA areas and the entire population sample of 990 residents in non-MDA areas were ICT negative. In MDA areas, a total of 3,152 female Cx. quinquefasciatus mosquitoes in 277 households (range, 0-296 mosquitoes per house) were collected via aspiration. RT-qPCR of 233 pools of mosquitos were negative for W. bancrofti RNA; an independent reference laboratory confirmed these results. These results provide evidence that LF transmission has been halted in this setting. |
Building the vector in: construction practices and the invasion and persistence of Anopheles stephensi in Jigjiga, Ethiopia
Yared S , Gebresilassie A , Aklilu E , Abdulahi E , Kirstein OD , Gonzalez-Olvera G , Che-Mendoza A , Bibiano-Marin W , Waymire E , Lines J , Lenhart A , Kitron U , Carter T , Manrique-Saide P , Vazquez-Prokopec GM . Lancet Planet Health 2023 7 (12) e999-e1005 Anopheles stephensi is a major vector of malaria in Asia and the Arabian Peninsula, and its recent invasion into Africa poses a major threat to malaria control and elimination efforts on the continent. The mosquito is well adapted to urban environments, and its presence in Africa could potentially lead to an increase in malaria transmission in cities. Most of the knowledge about An stephensi ecology in Africa has been generated from studies conducted during the rainy season, when vectors are most abundant. Here, we provide evidence from the peak of the dry season in the city of Jigjiga in Ethiopia, and report An stephensi immature stages infesting predominantly in water reservoirs made to support construction operations (ie, in construction sites or associated with brick-manufacturing businesses). Political and economic changes in Ethiopia (particularly the Somali Region) have fuelled an unprecedented construction boom since 2018 that, in our opinion, has been instrumental in the establishment, persistence, and propagation of An stephensi via the year-round availability of perennial larval habitats associated with construction. We argue that larval source management during the dry season might provide a unique opportunity for focused control of An stephensi in Jigjiga and similar areas. |
Notes from the field: Locally acquired mosquito-transmitted (autochthonous) plasmodium falciparum malaria - national capital region, Maryland, August 2023
Duwell M , DeVita T , Torpey D , Chen J , Myers RA , Mace K , Ridpath AD , Odongo W , Raphael BH , Lenhart A , Tongren JE , Stanley S , Blythe D . MMWR Morb Mortal Wkly Rep 2023 72 (41) 1123-1125 Although malaria was eliminated in the United States in the mid-1950s, approximately 2,000 malaria cases are imported into the United States from regions with endemic disease transmission each year, including approximately 200 in Maryland* (Figure) (1). Anopheles mosquito species that can transmit malaria exist in many areas in the United States (2). Locally acquired mosquito-transmitted (i.e., autochthonous) cases have not been identified since 2003; however, these imported cases represent a potential source of infection. In mid-2023, eight autochthonous malaria cases (Plasmodium vivax) were identified in Florida and Texas (3); in both states, the autochthonous cases occurred in the vicinity of an imported malaria case. |
Outbreak of locally acquired mosquito-transmitted (autochthonous) malaria - Florida and Texas, May-July 2023
Blackburn D , Drennon M , Broussard K , Morrison AM , Stanek D , Sarney E , Ferracci C , Huard S , Brennan W , Eaton J , Nealeigh S , Barber N , Zimler RA , Adams JN , Blackmore C , Gordillo M , Mercado R , Vore H , Scanlan K , Motie I , Stanfield L , Farooq A , Widel K , Tomson K , Kerr N , Nasir J , Cone M , Rice C , Larkin T , Hernandez E , Bencie J , Lesser CR , Dersch M , Ramirez-Lachmann S , Clark M , Rollo S , Bashadi A , Tyler R , Bolling B , Moore B , Sullivan B , Fonken E , Castillo R , Gonzalez Y , Olivares G , Mace KE , Sayre D , Lenhart A , Sutcliffe A , Dotson E , Corredor C , Rogers E , Raphael BH , Sapp SGH , Qvarnstrom Y , Ridpath AD , McElroy PD . MMWR Morb Mortal Wkly Rep 2023 72 (36) 973-978 Eight cases of locally acquired, mosquito-transmitted (i.e., autochthonous) Plasmodium vivax malaria, which has not been reported in the United States since 2003, were reported to CDC from state health departments in Florida and Texas during May 18-July 17, 2023. As of August 4, 2023, case surveillance, mosquito surveillance and control activities, and public outreach and education activities continue in both states. U.S. clinicians need to consider a malaria diagnosis in patients with unexplained fever, especially in areas where autochthonous malaria has been recently reported, although the risk for autochthonous malaria in the United States remains very low. Prompt diagnosis and treatment of malaria can prevent severe disease or death and limit ongoing transmission to local Anopheles mosquitoes and other persons. Preventing mosquito bites and controlling mosquitoes at home can prevent mosquitoborne diseases, including malaria. Before traveling internationally to areas with endemic malaria, travelers should consult with a health care provider regarding recommended malaria prevention measures, including potentially taking malaria prophylaxis. Malaria is a nationally notifiable disease; continued reporting of malaria cases to jurisdictional health departments and CDC will also help ensure robust surveillance to detect and prevent autochthonous malaria in the United States. |
Comparative transcriptomic analysis of insecticide-resistant Aedes aegypti from Puerto Rico reveals insecticide-specific patterns of gene expression
Derilus D , Impoinvil LM , Muturi EJ , McAllister J , Kenney J , Massey SE , Hemme R , Kothera L , Lenhart A . Genes (Basel) 2023 14 (8) Aedes aegypti transmits major arboviruses of public health importance, including dengue, chikungunya, Zika, and yellow fever. The use of insecticides represents the cornerstone of vector control; however, insecticide resistance in Ae. aegypti has become widespread. Understanding the molecular basis of insecticide resistance in this species is crucial to design effective resistance management strategies. Here, we applied Illumina RNA-Seq to study the gene expression patterns associated with resistance to three widely used insecticides (malathion, alphacypermethrin, and lambda-cyhalothrin) in Ae. aegypti populations from two sites (Manatí and Isabela) in Puerto Rico (PR). Cytochrome P450s were the most overexpressed detoxification genes across all resistant phenotypes. Some detoxification genes (CYP6Z7, CYP28A5, CYP9J2, CYP6Z6, CYP6BB2, CYP6M9, and two CYP9F2 orthologs) were commonly overexpressed in mosquitoes that survived exposure to all three insecticides (independent of geographical origin) while others including CYP6BY1 (malathion), GSTD1 (alpha-cypermethrin), CYP4H29 and GSTE6 (lambda-cyhalothrin) were uniquely overexpressed in mosquitoes that survived exposure to specific insecticides. The gene ontology (GO) terms associated with monooxygenase, iron binding, and passive transmembrane transporter activities were significantly enriched in four out of six resistant vs. susceptible comparisons while serine protease activity was elevated in all insecticide-resistant groups relative to the susceptible strain. Interestingly, cuticular-related protein genes (chinase and chitin) were predominantly downregulated, which was also confirmed in the functional enrichment analysis. This RNA-Seq analysis presents a detailed picture of the candidate detoxification genes and other pathways that are potentially associated with pyrethroid and organophosphate resistance in Ae. aegypti populations from PR. These results could inform development of novel molecular tools for detection of resistance-associated gene expression in this important arbovirus vector and guide the design and implementation of resistance management strategies. |
Rapid Evolution of Knockdown Resistance Haplotypes in Response to Pyrethroid Selection in Aedes aegypti (preprint)
Baltzegar J , Vella M , Gunning C , Vasquez G , Astete H , Stell F , Fisher M , Scott TW , Lenhart A , Lloyd AL , Morrison A , Gould F . bioRxiv 2021 2021.04.02.438212 This study describes the evolution of knockdown resistance (kdr) haplotypes in Aedes aegypti in response to pyrethroid insecticide use over the course of 18 years in Iquitos, Peru. Based on the duration and intensiveness of sampling (∼10,000 samples), this is the most thorough study of kdr population genetics in Ae. aegypti to date within a city. We provide evidence for the direct connection between programmatic citywide pyrethroid spraying and the increase in frequency of specific kdr haplotypes by identifying two evolutionary events in the population. The relatively high selection coefficients, even under infrequent insecticide pressure, emphasizes how quickly populations can evolve. The observed rapid increase in frequency of resistance alleles might have been aided by the incomplete dominance of resistance-conferring alleles over corresponding susceptibility alleles. In addition to dramatic temporal shifts, spatial suppression experiments reveal that genetic heterogeneity existed not only at the citywide scale, but also on a very fine scale within the city.Competing Interest StatementThe authors have declared no competing interest. |
A whole transcriptomic approach reveals novel mechanisms of organophosphate and pyrethroid resistance in Anopheles arabiensis from Ethiopia (preprint)
Messenger LA , Impoinvil LM , Derilus D , Yewhalaw D , Irish S , Lenhart A . bioRxiv 2021 2021.07.09.451871 The development of insecticide resistance in malaria vectors is of increasing concern in Ethiopia because of its potential implications for vector control failure. To better elucidate the specificity of resistance mechanisms and to facilitate the design of control strategies that minimize the likelihood of selecting for cross-resistance, a whole transcriptomic approach was used to explore gene expression patterns in a multi-insecticide resistant population of Anopheles arabiensis from Oromia Region, Ethiopia. This field population was resistant to the diagnostic doses of malathion (average mortality of 71.9%) and permethrin (77.4%), with pools of survivors and unexposed individuals analyzed using Illumina RNA-sequencing, alongside insecticide susceptible reference strains. This population also demonstrated deltamethrin resistance but complete susceptibility to alpha-cypermethrin, bendiocarb and propoxur, providing a phenotypic basis for detecting insecticide-specific resistance mechanisms. Transcriptomic data revealed overexpression of genes including cytochrome P450s, glutathione-s-transferases and carboxylesterases (including CYP4C36, CYP6AA1, CYP6M2, CYP6M3, CYP6P4, CYP9K1, CYP9L1, GSTD3, GSTE2, GSTE3, GSTE4, GSTE5, GSTE7 and two carboxylesterases) that were shared between malathion and permethrin survivors. We also identified nineteen highly overexpressed cuticular-associated proteins (including CYP4G16, CYP4G17 and chitinase) and eighteen salivary gland proteins (including D7r4 short form salivary protein), which may be contributing to a non-specific resistance phenotype by either enhancing the cuticular barrier or promoting binding and sequestration of insecticides, respectively. These findings provide novel insights into the molecular basis of insecticide resistance in this lesser well-characterized major malaria vector species.Importance Insecticide-resistant mosquito populations remain a significant challenge to global malaria vector control. While substantial progress has been made unraveling resistance mechanisms in major vector species, such as Anopheles gambiae and An. funestus, comparatively less is known about An. arabiensis populations. Using a whole transcriptomic approach, we investigated genes associated with resistance to insecticides used to control An. arabiensis in Ethiopia. Study findings revealed shared detoxification genes between organophosphate- and pyrethroid-resistant vectors and highly overexpressed cuticular-associated proteins and salivary gland proteins, which may play a role in enhancing insecticide resistance. The whole transcriptomic analysis detected novel resistance-associated genes, which warrant functional validation to determine their specificity to particular insecticides and their potential to confer cross-resistance between different insecticides with the same mode of action. These genes may contribute to the development of diagnostic markers to monitor insecticide resistance dynamics in the field. |
Western Kenyan Anopheles gambiae s.s. showing intense permethrin resistance harbor distinct microbiota (preprint)
Omoke D , Kipsum M , Otieno S , Esalimba E , Sheth M , Lenhart A , Njeru EM , Ochomo E , Dada N . bioRxiv 2020 2020.11.12.378760 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, we comparatively characterized the microbiota of An. gambiae s.s. from Tulukuyi village, Bungoma, Kenya, with differing permethrin resistance profiles.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 (107.5μg/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 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 (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.Conclusion 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. Our 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 malaria vectors, and potentially identifying novel microbial markers of insecticide resistance that could supplement existing vector surveillance tools.Competing Interest StatementThe authors have declared no competing interest. |
Evaluation of the durability of long-lasting insecticidal nets in Guatemala (preprint)
Castellanos ME , Rodas S , Juárez JG , Lol JC , Chanquin S , Morales Z , Vizcaino L , Smith SC , Vanden Eng J , Woldu HG , Lenhart A , Padilla N . medRxiv 2020 2020.07.30.20165316 Background Insecticide-treated bednets (ITNs) are widely used for the prevention and control of malaria. In Guatemala, since 2006, ITNs have been distributed free of charge in the highest risk malaria-endemic areas and constitute one of the primary vector control measures in the country. Despite relying on ITNs for almost 15 years, there is a lack of data to inform the timely replacement of ITNs whose effectiveness becomes diminished by routine use.Methods We assessed the survivorship, physical integrity, insecticide content and bio-efficacy of ITNs through cross-sectional surveys conducted at 18, 24 and 32 months after a 2012 distribution of PermaNet® 2.0 in a malaria focus in Guatemala. A total of 988 ITNs were analyzed (290 at 18 months, 349 at 24 months and 349 at 32 months).Results The functional survivorship of bednets decreased over time, from 92% at 18 months, to 81% at 24 months and 69% at 32 months. Independent of the time of the survey, less than 80% of the bednets that were still present in the household were reported to have been used the night before. Most of the bednets had been washed at least once (88% at 18 months, 92% at 24 months and 96% at 32 months). The proportion of bednets categorized as “in good condition” per WHO guidelines of the total hole surface area, diminished from 77% at 18 months to 58% at 32 months. The portion of ITNs with deltamethrin concentration less than 10mg/m2 increased over time (14% at 18 months, 23% at 24 months, and 35% at 32 months). Among the bednets for which bioassays were conducted, the percentage that met WHO criteria for efficacy dropped from 90% at 18 months to 52% at 32 months.Conclusion While our assessment demonstrated that nets were in relatively good physical condition over time, the combination of declining bio-efficacy over time and low use rates limited the overall effectiveness of the LLINs. Efforts to encourage the community to retain, use, and properly care for the LLINs may improve their impact. Durability assessments should be included in future campaigns.Competing Interest StatementThe authors have declared no competing interest.Funding StatementThe funding for this study was provided by the United States Agency for International Development (USAID) via the Amazon Malaria Initiative (AMI), Centers for Disease Control and Prevention (CDC) of the United States of America, Guatemalan Ministry of Public Health and Social Welfare and Center for Health Studies and Universidad del Valle de Guatemala. The funding bodies had no role in the design of the study and collection, analysis, and interpretation of the data and in writing the manuscript.Author DeclarationsI confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained.YesThe details of the IRB/oversight body that provided approval or exemption for the research described are given below:Oral informed consent was obtained from all participants prior to study inclusion. This study was approved by the Ethics Committee of the Center for Health Studies at Universidad del Valle de Guatemala (Approval Number: 081-06-2013); CDC investigators were not considered to be engaged in human subjects research.All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived.YesI understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance).YesI have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable.YesThe data that support the findings of this study are availa le on request from the senior author, NP. The data are not publicly available due to containing information that could compromise the privacy of participants.GISgeographic information systemGISgeographic information systemGPSGlobal positioning systemIQRinterquartile rangeITNInsecticide-treated bednetLLINlong-lasting insecticide-treated bednetLOESSLocally Weighted Scatterplot SmoothingMoHMinistry of HealthPDApersonal digital assistantTHSAtotal hole surface areatmmedian survival timeWHOWorld Health OrganizationXRFx-ray fluorescence |
Geographic heterogeneity in Anopheles albimanus microbiota is lost within one generation of laboratory colonization (preprint)
Dada N , Benedict AC , López F , Lol JC , Sheth M , Dzuris N , Padilla N , Lenhart A . bioRxiv 2020 2020.06.02.129619 Research on mosquito-microbe interactions may lead to new tools for mosquito and mosquito-borne disease control. To date, such research has largely utilized laboratory-reared mosquitoes that may lack the microbial diversity of wild populations. To better understand how mosquito microbiota may vary across different geographic locations and upon laboratory colonization, we characterized the microbiota of F1 progeny of wild-caught adult Anopheles albimanus from four locations in Guatemala using high throughput 16S rRNA amplicon sequencing. A total of 132 late instar larvae and 135 2-5day old, non-blood-fed virgin adult females were reared under identical laboratory conditions, pooled (3 individuals/pool) and analyzed. Larvae from mothers collected at different sites showed different microbial compositions (p=0.001; F = 9.5), but these differences were no longer present at the adult stage (p=0.12; F = 1.6). This indicates that mosquitoes retain a significant portion of their field-derived microbiota throughout immature development but shed them before or during adult eclosion. This is the first time the microbiota of F1 progeny of wild-caught mosquitoes has been characterized in relation to parental collection site, and our findings provide evidence that geographically associated heterogeneity in microbiota composition persists for a single generation, but only until the end of the larval stage. These findings advance our understanding of how the mosquito microbiota is altered upon first laboratory colonization, and raises considerations for how mosquito microbiome research may be extended beyond the laboratory to field settings.Competing Interest StatementThe authors have declared no competing interest. |
Insecticide resistance status of Aedes aegypti in Bangladesh (preprint)
Al-Amin HM , Johora FT , Irish SR , Hossainey MRH , Vizcaino L , Paul KK , Khan WA , Haque R , Alam MS , Lenhart A . bioRxiv 2020 2020.07.31.231076 Background Arboviral diseases including dengue and chikungunya are major public health concern in Bangladesh, with unprecedented levels of transmission reported in recent years. The primary approach to control these diseases is control of Aedes aegypti using pyrethroid insecticides. Although chemical control is long-practiced, no comprehensive analysis of Ae. aegypti susceptibility to insecticides has previously been conducted. This study aimed to determine the insecticide resistance status of Ae. aegypti in Bangladesh and investigate the role of detoxification enzymes and altered target site sensitivity as resistance mechanisms.Methods Aedes eggs were collected using ovitraps from five districts across the country and in eight neighborhoods of the capital city Dhaka from August to November 2017. CDC bottle bioassays were conducted for permethrin, deltamethrin, malathion, and bendiocarb using 3-5-day old F0-F2 non-blood fed female mosquitoes. Biochemical assays were conducted to detect metabolic resistance mechanisms and real-time PCR was performed to determine the frequencies of the knockdown resistance (kdr) mutations Gly1016, Cys1534, and Leu410.Results High levels of resistance to permethrin were detected in all Ae. aegypti populations, with mortality ranging from 0 – 14.8% at the diagnostic dose. Substantial resistance continued to be detected against higher (2X) doses of permethrin (5.1 – 44.4% mortality). Susceptibility to deltamethrin and malathion varied between populations while complete susceptibility to bendiocarb was observed in all populations. Significantly higher levels of esterase and oxidase activity were detected in most of the test populations as compared to the susceptible reference Rockefeller strain. A significant association was detected between permethrin resistance and the presence of Gly1016 and Cys1534 homozygotes. The frequency of kdr alleles varied across the Dhaka populations, and Leu410 was not detected in any of the tested populations.Conclusions The detection of widespread pyrethroid resistance and multiple mechanisms highlights the urgency for implementing alternate Ae. aegypti control strategies. In addition, implementing routine monitoring of insecticide resistance in Ae. aegypti in Bangladesh will lead to a greater understanding of susceptibility trends over space and time, thereby enabling the development of improved control strategies.Competing Interest StatementThe authors have declared no competing interest.AChEacetylcholine esterase;BIBreteau Index;β-ESTβ esterase;CIconfidence intervals;DDTdichlorodiphenyltrichloroethane;DTNBdithio-bis-2-nitrobenzoic acid;GSTsglutathione S-transferases;HWEHardy-Weinberg equilibrium;IRSindoor residual spraying;IACHEinsensitive acetylcholine esterase;icddr,bInternational Centre for Diarrhoeal Disease Research, Bangladesh;kdrknockdown resistance:LLINslong-lasting insecticidal nets:MFOsmixed-function oxidases;ODoptical density;ROCKRockefeller;CDCU.S. Centers for Disease Control and Prevention;VGSCvoltage-gated sodium channel;WHOWorld Health Organization |
Pyrethroid exposure alters Anopheles albimanus microbiota and resistant mosquitoes harbor more insecticide-metabolizing bacteria (preprint)
Dada N , Lol JC , Benedict AC , Lopez F , Sheth M , Dzuris N , Padilla N , Lenhart A . bioRxiv 2019 537480 A deeper understanding of the mechanisms underlying insecticide resistance is needed to mitigate its threat to malaria vector control. Building upon our earlier identified associations between mosquito microbiota and insecticide resistance, we demonstrate for the first time, type-specific effects of pyrethroid exposure on internal and cuticle surface bacteria in adult progeny of field-collected Anopheles albimanus. In contrast, larval cuticle surface—but not internal—bacteria were affected by pyrethroid exposure. Being over five-folds more abundant in pyrethroid resistant adults, as compared to susceptible or non-insecticide-exposed mosquitoes, Klebsiella (alphacypermethrin), Pantoea and Asaia (permethrin) were identified as potential markers of pyrethroid resistance in An. albimanus. We also show for the first time that An. albimanus larvae and adult cuticles harbor more diverse bacterial communities than their internal microbial niches. Our findings indicate insecticide selection pressures on mosquito microbiota, and support the hypothesis of an undescribed microbe-mediated mechanism of insecticide metabolism in mosquitoes. |
Mechanisms associated with pyrethroid resistance in populations of Aedes aegypti (Diptera: Culicidae) from the Caribbean coast of Colombia (preprint)
Pareja-Loaiza PX , Santacoloma Varon L , Rey Vega G , Gómez-Camargo D , Maestre-Serrano R , Lenhart A . bioRxiv 2020 2020.01.23.916577 Aedes aegypti is the main vector of dengue, chikungunya, and Zika viruses, which are of great public health importance in Colombia. Aedes control strategies in Colombia rely heavily on the use of organophosphate and pyrethroid insecticides, providing constant selection pressure and the emergence of resistant populations. In recent years, insecticide use has increased due to the increased incidence of dengue and recent introductions of chikungunya and Zika. In the present study, pyrethroid resistance was studied across six populations of A. aegypti from the Caribbean coast of Colombia. Susceptibility to λ-cyhalothrin, deltamethrin, and permethrin was assessed, and resistance intensity was determined. Activity levels of enzymes associated with resistance were measured, and the frequencies of three kdr alleles (V1016I, F1534C, V410L) were calculated. Results showed variations in pyrethroid susceptibility across A. aegypti populations and altered enzyme activity levels were detected. The kdr alleles were detected in all populations, with high variations in frequencies: V1016I (frequency ranging from 0.15–0.70), F1534C (range 0.94–1.00), and V410L (range 0.05–0.72). In assays of phenotyped individuals, associations were observed between the presence of V1016I, F1534C, and V410L alleles and resistance to the evaluated pyrethroids, as well as between the VI1016/CC1534/VL410 tri-locus genotype and λ-cyhalothrin and permethrin resistance. The results of the present study contribute to the knowledge of the mechanisms underlying the resistance to key pyrethroids used to control A. aegypti along the Caribbean coast of Colombia. |
Building the vector in? Construction practices contribute to the invasion and persistence of Anopheles stephensi in Jigjiga, Ethiopia (preprint)
Yared S , Gebresilassie A , Aklilu E , Abdulahi E , Kirstein OD , Gonzalez-Olvera G , Che-Mendoza A , Bibiano-Marin W , Waymire E , Lines J , Lenhart A , Kitron U , Carter T , Manrique-Saide P , Vazquez-Prokopec GM . bioRxiv 2023 24 Anopheles stephensi is a major vector of malaria in Asia and the Arabian Peninsula, and its recent invasion into Africa poses a significant threat to malaria control and elimination efforts on the continent. The mosquito is well-adapted to urban environments, and its presence in Africa could potentially lead to an increase in malaria transmission in cities. Most of the knowledge about An. stephensi ecology in Africa has been generated from studies conducted during the rainy season, when vectors are most abundant. Here, we provide evidence from the peak of the dry season in the city of Jigjiga, Ethiopia, and report the finding of An. stephensi immature stages infesting predominantly water reservoirs made to support construction operations (in construction sites or associated with brick manufacturing businesses). Political and economic changes in Ethiopia (and particularly the Somali Region) have fueled an unprecedented construction boom since 2018 that, in our opinion, has been instrumental in the establishment, persistence and propagation of An. stephensi via the year-round availability of perennial larval habitats associated with construction. We argue that larval source management during the dry season may provide a unique opportunity for focused control of An. stephensi in Jigjiga and similar areas. Copyright The copyright holder for this preprint is the author/funder, who has granted bioRxiv a license to display the preprint in perpetuity. It is made available under a CC-BY-NC-ND 4.0 International license. |
Insecticide resistance levels and associated mechanisms in three Aedes aegypti populations from Venezuela
Rubio-Palis Y , Dzuris N , Sandi C , Vizcaino-Cabarrus RL , Corredor-Medina C , González JA , Lenhart AE . Mem Inst Oswaldo Cruz 2023 118 e220210 BACKGROUND: The massive use of insecticides in public health has exerted selective pressure resulting in the development of resistance in Aedes aegypti to different insecticides in Venezuela. Between 2010 and 2020, the only insecticides available for vector control were the organophosphates (Ops) fenitrothion and temephos which were focally applied. OBJECTIVES: To determine the state of insecticide resistance and to identify the possible biochemical and molecular mechanisms involved in three populations of Ae. aegypti from Venezuela. METHODS: CDC bottle bioassays were conducted on Ae. aegypti collected between October 2019 and February 2020 in two hyperendemic localities for dengue in Aragua State and in a malaria endemic area in Bolívar State. Insecticide resistance mechanisms were studied using biochemical assays and polymerase chain reaction (PCR) to detect kdr mutations. FINDINGS: Bioassays showed contrasting results among populations; Las Brisas was resistant to malathion, permethrin and deltamethrin, Urbanización 19 de Abril was resistant to permethrin and Nacupay to malathion. All populations showed significantly higher activity of mixed function oxidases and glutathione-S-transferases (GSTs) in comparison with the susceptible strain. The kdr mutations V410L, F1534C, and V1016I were detected in all populations, with F1534C at higher frequencies. MAIN CONCLUSION: Insecticide resistance persists in three Ae. aegypti populations from Venezuela even in the relative absence of insecticide application. |
Public health impact of the spread of Anopheles stephensi in the WHO Eastern Mediterranean Region countries in Horn of Africa and Yemen: need for integrated vector surveillance and control
Al-Eryani SM , Irish SR , Carter TE , Lenhart A , Aljasari A , Montoya LF , Awash AA , Mohammed E , Ali S , Esmail MA , Hussain A , Amran JG , Kayad S , Nouredayem M , Adam MA , Azkoul L , Assada M , Baheshm YA , Eltahir W , Hutin YJ . Malar J 2023 22 (1) 187 BACKGROUND: Anopheles stephensi is an efficient vector of both Plasmodium falciparum and Plasmodium vivax in South Asia and the Middle East. The spread of An. stephensi to countries within the Horn of Africa threatens progress in malaria control in this region as well as the rest of sub-Saharan Africa. METHODS: The available malaria data and the timeline for the detection of An. stephensi was reviewed to analyse the role of An. stephensi in malaria transmission in Horn of Africa of the Eastern Mediterranean Region (EMR) in Djibouti, Somalia, Sudan and Yemen. RESULTS: Malaria incidence in Horn of Africa of EMR and Yemen, increased from 41.6 in 2015 to 61.5 cases per 1000 in 2020. The four countries from this region, Djibouti, Somalia, Sudan and Yemen had reported the detection of An. stephensi as of 2021. In Djibouti City, following its detection in 2012, the estimated incidence increased from 2.5 cases per 1000 in 2013 to 97.6 cases per 1000 in 2020. However, its contribution to malaria transmission in other major cities and in other countries, is unclear because of other factors, quality of the urban malaria data, human mobility, uncertainty about the actual arrival time of An. stephensi and poor entomological surveillance. CONCLUSIONS: While An. stephensi may explain a resurgence of malaria in Djibouti, further investigations are needed to understand its interpretation trends in urban malaria across the greater region. More investment for multisectoral approach and integrated surveillance and control should target all vectors particularly malaria and dengue vectors to guide interventions in urban areas. |
Insecticide resistance compromises the control of Aedes aegypti in Bangladesh.
Al-Amin HM , Gyawali N , Graham M , Alam MS , Lenhart A , Hugo LE , Rašić G , Beebe NW , Devine GJ . Pest Manag Sci 2023 79 (8) 2846-2861 BACKGROUND: With no effective drugs or widely available vaccines, dengue control in Bangladesh is dependent on targeting the primary vector Aedes aegypti with insecticides and larval source management. Despite these interventions, the dengue burden is increasing in Bangladesh, and the country experienced its worst outbreak in 2019 with 101,354 hospitalized cases. This may be partially facilitated by the presence of intense insecticide resistance in vector populations. Here, we describe the intensity and mechanisms of resistance to insecticides commonly deployed against Ae. aegypti in Dhaka, Bangladesh. RESULTS: Dhaka Ae. aegypti colonies exhibited high-intensity resistance to pyrethroids. Using CDC bottle assays, we recorded 2 - 24% mortality (recorded at 24 hours) to permethrin and 48 - 94% mortality to deltamethrin, at 10x the diagnostic dose. Bioassays conducted using insecticide-synergist combinations suggested that metabolic mechanisms were contributing to pyrethroid resistance, specifically multi-function oxidases, esterases, and glutathione S-transferases. In addition, kdr alleles were detected, with a high frequency (78-98%) of homozygotes for the V1016G mutation. A large proportion (≤ 74%) of free-flying and resting mosquitoes from Dhaka colonies survived exposure to standard applications of pyrethroid aerosols in an experimental free-flight room. Although that exposure affected Ae. aegypti's immediate host-seeking behavior, the effect was transient in surviving mosquitoes. CONCLUSION: The intense resistance characterized in this study is likely compromising the operational effectiveness of pyrethroids against Ae. aegypti in Dhaka. Switching to alternative chemical classes may offer a medium-term solution, but ultimately a more sustainable and effective approach to controlling dengue vectors is required. This article is protected by copyright. All rights reserved. |
A new WHO bottle bioassay method to assess the susceptibility of mosquito vectors to public health insecticides: results from a WHO-coordinated multi-centre study
Corbel V , Kont MD , Ahumada ML , Andréo L , Bayili B , Bayili K , Brooke B , Pinto Caballero JA , Lambert B , Churcher TS , Duchon S , Etang J , Flores AE , Gunasekaran K , Juntarajumnong W , Kirby M , Davies R , Lees RS , Lenhart A , Lima JBP , Martins AJ , Müller P , N'Guessan R , Ngufor C , Praulins G , Quinones M , Raghavendra K , Verma V , Rus AC , Samuel M , Ying KS , Sungvornyothin S , Uragayala S , Velayudhan R , Yadav RS . Parasit Vectors 2023 16 (1) 21 BACKGROUND: The continued spread of insecticide resistance in mosquito vectors of malaria and arboviral diseases may lead to operational failure of insecticide-based interventions if resistance is not monitored and managed efficiently. This study aimed to develop and validate a new WHO glass bottle bioassay method as an alternative to the WHO standard insecticide tube test to monitor mosquito susceptibility to new public health insecticides with particular modes of action, physical properties or both. METHODS: A multi-centre study involving 21 laboratories worldwide generated data on the susceptibility of seven mosquito species (Aedes aegypti, Aedes albopictus, Anopheles gambiae sensu stricto [An. gambiae s.s.], Anopheles funestus, Anopheles stephensi, Anopheles minimus and Anopheles albimanus) to seven public health insecticides in five classes, including pyrethroids (metofluthrin, prallethrin and transfluthrin), neonicotinoids (clothianidin), pyrroles (chlorfenapyr), juvenile hormone mimics (pyriproxyfen) and butenolides (flupyradifurone), in glass bottle assays. The data were analysed using a Bayesian binomial model to determine the concentration-response curves for each insecticide-species combination and to assess the within-bioassay variability in the susceptibility endpoints, namely the concentration that kills 50% and 99% of the test population (LC(50) and LC(99), respectively) and the concentration that inhibits oviposition of the test population by 50% and 99% (OI(50) and OI(99)), to measure mortality and the sterilizing effect, respectively. RESULTS: Overall, about 200,000 mosquitoes were tested with the new bottle bioassay, and LC(50)/LC(99) or OI(50)/OI(99) values were determined for all insecticides. Variation was seen between laboratories in estimates for some mosquito species-insecticide combinations, while other test results were consistent. The variation was generally greater with transfluthrin and flupyradifurone than with the other compounds tested, especially against Anopheles species. Overall, the mean within-bioassay variability in mortality and oviposition inhibition were < 10% for most mosquito species-insecticide combinations. CONCLUSION: Our findings, based on the largest susceptibility dataset ever produced on mosquitoes, showed that the new WHO bottle bioassay is adequate for evaluating mosquito susceptibility to new and promising public health insecticides currently deployed for vector control. The datasets presented in this study have been used recently by the WHO to establish 17 new insecticide discriminating concentrations (DCs) for either Aedes spp. or Anopheles spp. The bottle bioassay and DCs can now be widely used to monitor baseline insecticide susceptibility of wild populations of vectors of malaria and Aedes-borne diseases worldwide. |
Pyrethroid resistance in the New World malaria vector Anopheles albimanus is mediated by cytochrome P450 CYP6P5
Kusimo MO , Mackenzie-Impoinvil L , Ibrahim SS , Muhammad A , Irving H , Hearn J , Lenhart AE , Wondji CS . Pestic Biochem Physiol 2022 183 105061 Pyrethroid resistance in the malaria vector Anopheles albimanus presents an obstacle to malaria elimination in the Americas. Here, An. albimanus CYP6P5 (the most overexpressed P450 in a Peruvian population) was functionally characterized. Recombinant CYP6P5 metabolized the type II pyrethroids, deltamethrin and α-cypermethrin with comparable affinities (K(M) of 3.3 μM ± 0.4 and 3.6 μM ± 0.5, respectively), but exhibited a 2.7-fold higher catalytic rate for α-cypermethrin (k(cat) of 6.02 min(-1) ± 0.2) versus deltamethrin (2.68 min(-1) ± 0.09). Time-course assays revealed progressive depletion of the above pyrethroids with production of four HPLC-detectable metabolites. Low depletion was obtained with type I pyrethroid, permethrin. Transgenic expression in Drosophila melanogaster demonstrated that overexpression of CYP6P5 alone conferred type II pyrethroid resistance, with only 16% and 55.3% mortalities in flies exposed to 0.25% α-cypermethrin and 0.15% deltamethrin, respectively. Synergist bioassays using P450 inhibitor piperonylbutoxide significantly recovered susceptibility (mortality = 73.6%, p < 0.001) in synergized flies exposed to 4% piperonylbutoxide, plus 0.25% α-cypermethrin, compared to non-synergized flies (mortality = 4.9%). Moderate resistance was also observed towards 4% DDT. These findings established the preeminent role of CYP6P5 in metabolic resistance in An. albimanus, highlighting challenges associated with deployment of insecticide-based control tools in the Americas. |
Insecticide resistance intensity and efficacy of synergists with pyrethroids in Anopheles gambiae (Diptera: Culicidae) from Southern Togo.
Apetogbo Y , Ahadji-Dabla KM , Soma DD , Amoudji AD , Koffi E , Akagankou KI , Bamogo R , Ngaffo KL , Maiga S , Atcha-Oubou RT , Dorkenoo AM , Vizcaino L , Lenhart A , Diabaté A , Dabiré RK , Ketoh GK . Malar J 2022 21 (1) 353 BACKGROUND: This study was designed to provide insecticide resistance data for decision-making in terms of resistance management plans in Togo. METHODS: The susceptibility status of Anopheles gambiae sensu lato (s.l.) to insecticides used in public health was assessed using the WHO tube test protocol. Pyrethroid resistance intensity bioassays were performed following the CDC bottle test protocol. The activity of detoxification enzymes was tested using the synergists piperonyl butoxide, S.S.S-tributlyphosphorotrithioate and ethacrinic acid. Species-specific identification of An. gambiae s.l. and kdr mutation genotyping were performed using PCR techniques. RESULTS: Local populations of An. gambiae s.l. showed full susceptibility to pirimiphos methyl at Lomé, Kovié, Anié, and Kpèlè Toutou. At Baguida, mortality was 90%, indicating possible resistance to pirimiphos methyl. Resistance was recorded to DDT, bendiocarb, and propoxur at all sites. A high intensity of pyrethroid resistance was recorded and the detoxification enzymes contributing to resistance were oxidases, esterases, and glutathione-s-transferases based on the synergist tests. Anopheles gambiae sensu stricto (s.s.) and Anopheles coluzzii were the main species identified. High kdr L1014F and low kdr L1014S allele frequencies were detected at all localities. CONCLUSION: This study suggests the need to reinforce current insecticide-based malaria control interventions (IRS and LLINs) with complementary tools. |
Building the capacity of West African countries in Aedes surveillance: inaugural meeting of the West African Aedes Surveillance Network (WAASuN)
Dadzie SK , Akorli J , Coulibaly MB , Ahadji-Dabla KM , Baber I , Bobanga T , Boukhary Aoms , Canelas T , Facchinelli L , Gonalves A , Guelbeogo M , Kamgang B , Keita IK , Konan L , Levine R , Dzuris N , Lenhart A . Parasit Vectors 2022 15 (1) 381 Arboviral diseases such as dengue, Zika and chikungunya transmitted by Aedes mosquitoes have been reported in 34 African countries. Available data indicate that in recent years there have been dengue and chikungunya outbreaks in the West Africa subregion, in countries including Cte d'Ivoire, Burkina Faso, Gabon, Senegal, and Benin. These viral diseases are causing an increased public health burden, which impedes poverty reduction and sustainable development. Aedes surveillance and control capacity, which are key to reducing the prevalence of arboviral infections, need to be strengthened in West Africa, to provide information essential for the formulation of effective vector control strategies and the prediction of arboviral disease outbreaks. In line with these objectives, the West African Aedes Surveillance Network (WAASuN) was created in 2017 at a meeting held in Sierra Leone comprising African scientists working on Aedes mosquitoes. This manuscript describes the proceedings and discusses key highlights of the meeting. |
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