Biology subjects

Dengela, D.

Publications and source records attributed to Dengela, D..

6 recordsLinked to original sources

bioRxiv2025

Anopheles stephensi larval habitat superproductivity and its relevance for larval source management in Africa

The invasion of Africa by Anopheles stephensi poses a significant threat to malaria elimination. As An. stephensi exploits a wide array of urban artificial larval habitats, it may be less impacted by rainfall variability compared to other native Anopheles species. We empirically investigated this assumption by quantifying the seasonal transition of an established population from eastern Ethiopia between rainy and dry periods. Monthly larval surveys generated evidence of significant heterogeneity between seasons in the type of habitat and their productivity. As the dry season progressed, An. stephensi productivity significantly concentrated in large water reservoirs (for drinking and construction) to a point in which up to 77% of all larvae originated from 23% of the sites. Such superproductive sites were primarily water cisterns used for residential or construction purposes. A two-patch metapopulation model of An. stephensi linked to rainfall data recreated the seasonal larval dynamics observed in the field and predicted that larval control targeted on superproducer water reservoirs, when implemented at coverages higher than 60%, may lead to An. stephensi elimination. Our findings highlight the role of environmental variability in regulating An. stephensi populations and open the window for the deployment of control strategies that exploit major mosquito population bottlenecks.

ecology↗

bioRxiv2021

Tracking of Anopheles stephensi in Ethiopia using mitochondrial DNA reveals pattern of spread

The recent detection of the South Asian malaria vector Anopheles stephensi in the Horn of Africa (HOA) raises concerns about the impact of this mosquito on malaria transmission in the region. The mode and history of introduction is important for predicting the likelihood of continued introduction and future spread. Analysis of An. stephensi genetic diversity and population structure can provide insight into the history of the mosquito in the HOA. We investigated genetic diversity of An. stephensi in eastern Ethiopia where detection suggests a range expansion to this region to understand the history of this invasive population. We sequenced the cytochrome oxidase subunit I (COI) and cytochrome B gene (CytB) in 187 An. stephensi collected from 10 sites in Ethiopia in 2018. Phylogenetic analyses using a maximum-likelihood approach and minimum spanning network were conducted for Ethiopian sequences. Molecular identification of bloodmeal sources was also performed using universal vertebrate CytB sequencing. Six COI-CytB haplotypes were observed based on five segregating sites, with the highest number of haplotypes in the northeastern sites (Semera, Bati, and Gewana towns) relative to the southeastern sites (Kebridehar, Godey, and Degehabur) in eastern Ethiopia. In the phylogenetic and network analysis, we observed population differentiation based on the distribution of the haplotypes across the northeastern and central sites (Erer Gota, Dire Dawa, and Awash Sebat Kilo) compared to the southeastern sites and evidence of a South Asian origin of the HOA An. stephensi lineages. The presence of the putative South Asian haplotype of origin at sites closest to Ethiopias northeastern borders support route of introductions into Ethiopia from the northeast. Finally, molecular bloodmeal analysis revealed evidence of feeding on bovines, goats, dogs, and humans, as well as evidence of multiple (mixed) blood meals. In conclusion, we find support for the hypothesis for the recent expansion of An. stephensi into southeastern Ethiopia with multiple introductions. We also find evidence that supports the hypothesis that HOA An. stephensi populations originate from South Asia rather than the Arabian Peninsula. The evidence of both zoophagic and anthropophagic feeding support the potential for livestock movement to play a role in vector spread in this region.

ecology↗

bioRxiv2020

Anopheles stephensi as an emerging malaria vector in the Horn of Africa with high susceptibility to Ethiopian Plasmodium vivax and Plasmodium falciparum isolates

Anopheles stephensi, an efficient Asian malaria vector, recently spread into the Horn of Africa and may increase malaria receptivity in African urban areas. We assessed occurrence, genetic complexity, blood meal source and infection status of An. stephensi in Awash Sebat Kilo town, Ethiopia. We used membrane feeding assays to assess competence of local An. stephensi to P. vivax and P. falciparum isolates from clinical patients. 75.3% of the examined waterbodies were infested with An. stephensi developmental stages that were genetically closely related to isolates from Djibouti and Pakistan. Both P. vivax and P. falciparum were detected in wild-caught adult An. stephensi. Local An. stephensi was more receptive to P. vivax compared to a colony of An. arabiensis. We conclude that An. stephensi is an established vector in this part of Ethiopia, highly permissive for local P. vivax and P. falciparum isolates and presents an important new challenge for malaria control. Summary of the articleAn. stephensi, a metropolitan malaria vector that recently expanded to the Horn of African, was highly susceptible to local P. falciparum and P. vivax isolates from Ethiopia and may increase malariogenic potential of rapidly expanding urban settings in Africa.

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↗

bioRxiv2019

Geographical distribution of Anopheles stephensi in eastern Ethiopia

BackgroundThe recent detection of the South Asian malaria vector An. stephensi in Ethiopia and other regions in the Horn of Africa has raised concerns about its potential impact on malaria transmission. We report here findings of survey for this species in eastern Ethiopia using both morphological and molecular methods for species identification.\n\nMethodsAdult and larval/pupal collections were conducted at ten sites in eastern Ethiopia and Anopheles specimens species were determined using standard morphological keys and genetic analysis.\n\nResultsIn total, 2,231 morphologically identified An. stephensi were collected. A molecular approach incorporating both PCR endpoint assay and sequencing of portions of the internal transcribed spacer 2 (ITS2) and cytochrome oxidase I (COI) loci confirmed the identity of the An. stephensi in most cases (119/124 of the morphologically identified An. stephensi confirmed molecularly). Additionally, we observed Aedes aegypti larvae and pupae at many of the An. stephensi larval habitats.\n\nConclusionsOur findings show that An. stephensi is widely distributed in eastern Ethiopia and highlight the need for further surveillance in the southern, western and northern parts of the country and throughout the Horn of Africa.

ecology↗

bioRxiv2019

Analysis-ready datasets for insecticide resistance phenotype and genotype frequency in African malaria vectors

The impact of insecticide resistance in malaria vectors is poorly understood and quantified. Here a series of geospatial datasets for insecticide resistance in malaria vectors are provided so that trends in resistance in time and space can be quantified and the impact of resistance found in wild populations on malaria transmission in Africa can be assessed. Data are also provided for common genetic markers of resistance to support analyses of whether these genetic data can improve the ability to monitor resistance in low resource settings. Specifically, data have been collated and geopositioned for the prevalence of insecticide resistance, as measured by standard bioassays, in representative samples of individual species or species complexes. Data are provided for the Anopheles gambiae species complex, the Anopheles funestus subgroup, and for nine individual vector species. In addition, allele frequencies for known resistance associated markers in the Voltage-gated sodium channel (Vgsc) are provided. In total, eight analysis-ready, standardised, geopositioned datasets encompassing over 20,000 African mosquito collections between 1957 and 2017 are provided.

zoology↗