Biology subjects

Lobo, N. F.

Publications and source records attributed to Lobo, N. F..

7 recordsLinked to original sources

bioRxiv2025

A genomic toolkit for surveillance and elimination of the principal malaria vectors in Southeast Asia.

While substantial progress has been made toward malaria elimination in Southeast Asia, major challenges remain. The principal mosquito vectors, Anopheles dirus and Anopheles minimus, inhabit diverse ecological niches and exhibit a wide range of behavioural and physiological insecticide resistance phenotypes, complicating vector control efforts. In Africa, genomic surveillance has transformed our understanding of vector evolution and resistance, supported by open-access tools and data. Comparable resources for Southeast Asian vectors remain limited. Here, we release Adir1.0, a curated, analysis-ready catalog of 540 An. dirus whole-genome sequences, accessible for interactive cloud-based analysis via the malariagen-data-python application programming interface (API). Alongside, we provide an updated Amin1.0 API to enhance functionality and usability, enabling integrated analyses across historical and new datasets. We demonstrate these resources by performing the first exploratory population genomic analysis of An. dirus from Bangladesh, Thailand, and Cambodia, revealing population structure, candidate regions of physiological resistance, and genomic structural variation. Together, these resources provide a foundation for genomic surveillance studies to inform vector control and malaria elimination strategies in Southeast Asia.

genetics↗

bioRxiv2025

Efficacy of the BiteBarrier transfluthrin emanator against susceptible and resistant malaria and arbovirus vectors in the semi-field system in Tanzania

Controlling mosquito-borne diseases is increasingly challenging due to factors such as outdoor and early biting mosquitoes and logistical or behavioral barriers, particularly in displaced populations where the use and efficacy of core interventions are inadequate. This study evaluated the impact of BiteBarrier, a transfluthrin-based spatial emanator, over eight weeks of aging against multiple mosquito species in semi-field system simulating both indoor and outdoor settings. We assessed the protective efficacy using both landing rate and feeding success methods across five mosquito species, including pyrethroid susceptible Anopheles gambiae sensu stricto (s.s.) and Aedes aegypti, An. gambiae s.s. with knock down resistance (KDR), and pyrethroid resistant An. funestus and Culex quinquefasciatus with upregulation of mixed function oxidases. The results show that the feeding endpoint provides more robust estimates of protective efficacy compared to the landing endpoint. The BiteBarrier provided over 93% (95% CI: 92 - 93) protection indoors and 80% (95% CI: 78 - 81) outdoors against mosquito bites and substantial mortality 47% (95% CI: 43 - 53) indoor and 26% (95% CI: 22 - 30) outdoors, regardless of mosquito species or resistance status. Overall, the BiteBarrier shows potential as a tool for reducing mosquito bites and vectorial capacity, offering protection over at least eight weeks of use for both indoor and outdoor environments.

systems biology↗

bioRxiv2024

Field evaluation of a volatile pyrethroid spatial repellent and etofenprox-treated clothing for outdoor protection against forest malaria vectors in Cambodia

Cambodias goal to eliminate malaria by 2025 is challenged by persisting transmission in the countrys forest and forest fringe areas. People living in, or traveling to the forest, are exposed to malaria vector bites during the day due to Anopheles daytime biting; and during the night, due to low bed net use and open sleeping structures. Volatile pyrethroid spatial repellents (VPSRs), and insecticide treated clothing (ITC) may help address these gaps in protection. In this field study the authors evaluated the outdoor application of one passive, transfluthrin-based VPSR, four etofenprox-ITCs paired with a picaridin topical repellent, and a combination of VPSR and ITC against wild Anopheles landing in Cambodia. Mathematical modeling was also used to predict the reduction of vectorial capacity of these interventions. A 7x7 Latin-square (6 interventions and one control) was conducted over 49 collection nights in seven temporary, open structures in a forest in Mondulkiri Province, Cambodia. Pairs of participants conducted human landing catches (HLCs) from 18h00 to 06h00, with each collector conducting collections for six hours. A randomly selected subset of collected Anopheles were identified to species using molecular methods. The rate ratio of each intervention compared to the control on Anopheles landings was estimated using a mixed-effect negative binomial regression with intervention, structure, and collector-pair as fixed-effects, and with collection date and structure-night as random effects. The modeling assessment aims to predict the relative reduction in vectoral capacity. Initial calculations involved establishing a "baseline scenario" without intervention, utilizing biometric parameters for Anopheles dirus. Various scenarios accounting for intervention coverage and adherence were then considered. The study aims to update parameters using field study estimates for wild Anopheles, incorporating multiple semi-field estimates for interventions and accounting for the variability and uncertainty in parameter values. Of the total 8,294 Anopheles specimens collected, 15% (n=1,242) of specimens were confirmed to species or species group via PCR. Fifteen species were confirmed; Anopheles dirus Form A was predominant (n=429), followed by Anopheles maculatus (n=189), and Anopheles minimus (n=60). All six interventions reduced Anopheles landing substantially; protective efficacies ranged between 61% (95% confidence interval (CI): 48 - 71%) (etofenprox-ITC, washed) and 95% (95% CI: 93 - 96%) (combined VPSR and unwashed etofenprox-ITC). Finally, the modelling assessment demonstrates significant reductions in vectoral capacity, with the highest impact observed for the combined ITC and VPSR as well as the VPSR used alone, although effectiveness decreases with intervention aging, and variability exists in the magnitude of predicted reductions due to differences in experimental conditions. These transfluthrin-based VPSR and etofenprox ITC interventions have the potential to reduce outdoor and daytime Anopheles biting by providing substantial protection against Anopheles landing. One or more of these tools may play a valuable role in the push for elimination in Cambodia and the Greater Mekong Subregion if programs can achieve effective coverage.

ecology↗

bioRxiv2023

First detection of Anopheles stephensi in Ghana using molecular surveillance

The invasive Anopheles stephensi mosquito has been rapidly expanding in range in Africa over the last decade, spreading from the Indian sub-continent to several East African countries (Djibouti, Ethiopia, Sudan, Somalia and Kenya) and now in West Africa, Nigeria. The rapid expansion of this invasive vector poses a major threat to current malaria control and elimination efforts. In line with the WHOs strategy to stop the spread of this invasive species by enhancing surveillance and control measures in Africa, we incorporated morphological and molecular surveillance of An. stephensi into routine entomological surveillance of malaria vectors in the city of Accra, Ghana. Here, we report on the first detection of An. stephensi in Ghana. An. stephensi mosquitoes were confirmed using PCR and sequencing of the ITS2 regions. These findings highlight the urgent need for increased surveillance and response strategies to mitigate the spread of An. stephensi in Ghana.

ecology↗

bioRxiv2023

Inference for entomological semi-field experiments: Fitting a mathematical model assessing personal and community protection of vector-control interventions

The effectiveness of vector-control tools is often assessed by experiments as a reduction in mosquito landings using human landing catches (HLCs). However, HLCs alone only quantify a single characteristic and therefore do not provide information on the overall impacts of the intervention product. Using data from a recent semi-field study which used time-stratified HLCs, aspiration of non-landing mosquitoes, and blood feeding, we suggest a Bayesian inference approach for fitting such data to a stochastic model. This model considers both personal protection, through a reduction in biting, and community protection, from mosquito mortality and disarming (prolonged inhibition of blood feeding). Parameter estimates are then used to predict the reduction of vectorial capacity induced by etofenpox-treated clothing, picaridin topical repellents, transfluthrin spatial repellents and metofluthrin spatial repellents, as well as combined interventions for Plasmodium falciparum malaria in Anopleles minimus. Overall, all interventions had both personal and community effects, preventing biting and killing or disarming mosquitoes. This led to large estimated reductions in the vectorial capacity, with substantial impact even at low coverage. As the interventions aged, fewer mosquitoes were killed; however the impact of some interventions changed from killing to disarming mosquitoes. Overall, this inference method allows for additional modes of action, rather than just reduction in biting, to be parameterised and highlights the tools assessed as promising malaria interventions.

systems biology↗

bioRxiv2020

Genomic and microscopic evidence of stable high density and maternally inherited Wolbachia infections in Anopheles mosquitoes

Wolbachia, a widespread bacterium that can reduce pathogen transmission in mosquitoes, has been detected within populations of Anopheles (An.) malaria vectors. In the An. gambiae complex, the primary vectors in Sub-Saharan Africa, Wolbachia strains are at low density and infection frequencies in wild populations. PCR-independent evidence is required to determine whether Wolbachia strains are true endosymbionts in Anopheles given most studies to date have used nested-PCR to identify strains. Here we report high-density strains found in geographically diverse populations of An. moucheti and An. demeilloni. Fluorescent in situ hybridization localized a heavy infection in the ovaries of An. moucheti and maternal transmission was observed. Genome sequencing of both strains obtained genome depths and coverages comparable to other known infections. Notably, homologs of cytoplasmic incompatibility factor (cif) genes were present indicating these strains possess the capacity to induce the phenotype cytoplasmic incompatibility which allows Wolbachia to spread through populations. The characteristics of these two strains suggest they are ideal candidates for Wolbachia biocontrol strategies in Anopheles.

microbiology↗

bioRxiv2020

The need to harmonize insecticide resistance testing: methodology, intensity concentrations and molecular mechanisms evaluated in Aedes aegypti populations in Central America and Hispaniola

BackgroundThe Zika AIRS Project, a USAID-funded initiative worked across the Latin America and Caribbean regions from 2016 to 2019, as an emergency to contain the spread of the Zika virus. All entomological records in the target countries showed wide distribution and high abundance of Aedes aegypti populations, however the susceptibility profiles of these insects to insecticides commonly employed by vector control campaigns were in most cases incomplete or inexistent. In close collaboration with the Ministries of Health of individual countries, Zika-AIRS teams conducted insecticide susceptibility testing of an array of insecticides in A. aegypti populations of each country. Procedures applied met the standard international protocols instructed by the World Health Organization and Centers for Disease Control and Prevention. Methodology and main findingsThe insecticides tested were selected under categories such as pyrethroids, organophosphates and carbamate. Results showed A. aegypti populations displaying high and widely distributed resistance to all pyrethroids across countries, tolerance to organophosphates and full susceptibility to a carbamate. Key inconsistencies between testing methods are presented and discussed. Additionally, four kdr mutations were analyzed to detect molecular mechanisms of insecticide resistance. The screening for kdr mutations suggested the widespread nature of V1016I mutation, linked to pyrethroid resistance in A. aegypti populations distributed and sampled in the above mentioned regions. Conclusions and perspectivesThis multi-country study contributes with updated information to the public health decision-makers across Central America and the Caribbean. This study provided training and established technical networks for more effective and sustainable insecticide surveillance programs. Most but not all records of insecticide resistance in A. aegypti were consistent between methodologies, thus inconsistent issues are discussed here to call for further improvement in procedures and convey more practical guidelines for surveillance teams in countries where Aedes-borne diseases are endemic. Author summaryAt the forefront of the fight against arboviruses transmission is the insecticide-based vector control. All countries in the Latin American and Caribbean region invest valuable resources from their limited budget to acquire and implement insecticide-based tools, with non-existent or weak insecticide resistance monitoring programs. Hence, the USAID-funded Zika AIRS Project (ZAP) collaborated with the Ministries of Health of multiple countries to update the profile of susceptibility to insecticides in Aedes aegypti populations. We found widespread resistance to pyrethroid and organophosphate insecticides, which account to almost 100% of the products available to control adult mosquitoes. As we used both of World Health Organization and Centers for Disease Control and Prevention standard methods, we found many similarities and some inconsistencies in the susceptibility profiles obtained for the very same vector populations. Additionally, we obtained insight on potential molecular mechanisms of resistance across the countries, finding the kdr mutation V1016I possibly involved in loss of susceptibility. This study is the biggest cross-country update of insecticide resistance for Aedes aegypti in years, and it should be used as evidence for improving the selection of insecticides in these countries and a call for further support to maintain insecticide resistance monitoring programs.

ecology↗