Biology subjects

Samake, J. N.

Publications and source records attributed to Samake, J. N..

5 recordsLinked to original sources

bioRxiv2026

Evidence of Anopheles stephensi involvement in the transmission of Plasmodium vivax in Djibouti, 2024

PurposeAnopheles stephensi is a malaria mosquito vector that has been raising international concern due to its invasive nature in Africa, including the nation of Djibouti. Since its initial detection in Djibouti in 2012, malaria morbidity and mortality have increased exponentially in the county. While there is an observed association increase in human malaria cases since the arrival of An. stephensi, high-quality evidence of An. stephensi carrying infective sporozoites is essential to determine the role of the invasive vector in malaria dynamics in Djibouti. This study seeks to confirm the link between An. stephensi and malaria transmission in Djibouti and examine genetic relatedness between Djiboutian An. stephensi populations and populations across the Horn of Africa. Such information regarding the An. stephensi populations and the Plasmodium species they transmit is necessary to devise appropriate control strategies and limit malaria transmission within and beyond the country. MethodsOne hundred and ninety-six adult An. stephensi mosquitoes from Djibouti were collected, molecularly confirmed, analyzed for a portion of the cytochrome c oxidase subunit 1 (COI), and tested for infective sporozoites using a highly sensitive and specific multiplex circumsporozoite enzyme linked immunosorbent assay (csELISA) bead assay. The COI sequences of one hundred and fourteen samples were further used to characterize the population genetic structure of the sampled An. stephensi and its genetic relatedness to other An. stephensi populations across the Horn of Africa. ResultsAll 196 samples were morphologically and molecularly confirmed to be An. stephensi. Plasmodium vivax210 sporozoites were detected with a positivity rate of 1.02%. An analysis of the COI region showed that the infected An. stephensi have the most prevalent COI haplotypes of invasive An. stephensi circulating in the Horn of Africa. ConclusionsThe findings from this study confirm the involvement of An. stephensi in P. vivax transmission in Djibouti and describe the genetic relatedness of Djiboutian An. stephensi populations to other populations across the Horn of Africa. This highlights the threat of An. stephensi invasion and supports a rapid and comprehensive response to mitigate the harm that An. stephensi populations cause, particularly through surveillance and control of adult populations. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=119 SRC="FIGDIR/small/707780v1_ufig1.gif" ALT="Figure 1"> View larger version (22K): org.highwire.dtl.DTLVardef@19f762corg.highwire.dtl.DTLVardef@7624forg.highwire.dtl.DTLVardef@c7492borg.highwire.dtl.DTLVardef@194c11f_HPS_FORMAT_FIGEXP M_FIG C_FIG

molecular biology↗

bioRxiv2025

An evaluation of longitudinal Anopheles stephensi egg viability and resistance to desiccation over time

Anopheles stephensi, a malaria vector in South Asia and parts of the Middle East, has been detected as an invasive species in numerous African countries in recent years. It threatens to increase malaria disease burden and reverse gains made in malaria control and elimination over the past decades on the continent. To halt further expansion, it is critical to understand the biological characteristics that may have facilitated An. stephensi range expansion to Africa. In its invasive range, An. stephensi larvae have been found to colonize artificial containers, many of which are shared with Aedes aegypti. The success of Ae. aegypti as an invasive vector is often attributed to the use of artificial containers and the ability of Ae. aegypti eggs to remain viable in the absence of water for months. While An. stephensi is found in artificial containers, it is unclear whether the eggs can remain viable without water for extended periods. Anopheles stephensi eggs were reported to remain viable in soil for up to 12 days in a study done almost 100 years ago, but this work has not been revisited since. Thus, in this present study, we used egg batches (>100 eggs per batch) from two laboratory strains of An. stephensi (SDA500 and STE2) from South Asia and one Ae. aegypti strain (LVP-IB12) to evaluate 1) whether An. stephensi eggs can remain viable like Ae. aegypti when egg substrates are completely dried following standard insectary methods for drying out Aedes aegypti egg sheets, and 2) assess egg viability duration at varying temperatures (15{degrees}C, 20{degrees}C, 25{degrees}C 30{degrees}C, 35{degrees}C) when eggs are held on a moistened substrate in a high humidity environment. Anopheles stephensi egg viability and subsequent larval survival was observed consistently when moistened egg sheets were held at 15{degrees}C in a high humidity (>75% RH) environment for up to 14 days in both strains. Anopheles stephensi eggs were not viable when dried following standard insectary Aedes aegypti methods for drying out egg sheets, except when the protocol was amended to include a 15{degrees}C storage temperature. Though egg viability and larval survival was observed in the amended protocol for SDA500 and STE2 (16% and 21% respectively), it was significantly less than that of LVP-IB12 (83%) and was only observed in the egg batches stored for the shortest timepoint (seven days post egg collection, three days post complete drying of egg sheets). These findings suggest that An. stephensi may remain viable if eggs are transported under ideal conditions (15{degrees}C and >75% RH) through trade or commerce routes. Thus, the persistence of An. stephensi eggs in the absence of water should be considered in programs that engage in surveillance and control of An. stephensi in Africa.

ecology↗

bioRxiv2024

Insecticide resistance and population structure of the invasive malaria vector, Anopheles stephensi, from Fiq, Ethiopia

Anopheles stephensi invasion in Ethiopia poses a risk of increased malaria disease burden in the region. Thus, understanding the insecticide resistance profile and population structure of the recently detected An. stephensi population in Fiq, Ethiopia, is critical to inform vector control to stop the spread of this invasive malaria species in the country. Following entomological surveillance for An. stephensi in Fiq, Somali region, Ethiopia, we confirmed the presence of An. stephensi morphologically and molecularly in Fiq. Characterization of larval habitats and insecticide susceptibility tests revealed that Fiq An. stephensi is most often found in artificial containers and is resistant to most adult insecticides tested (organophosphates, carbamates, pyrethroids) except for pirimiphos-methyl and PBO-pyrethroids. However, the immature larval stage was susceptible to temephos. Further comparative genomic analyses with previous An. stephensi populations from Ethiopia using 1,704 biallelic SNPs revealed genetic relatedness between Fiq An. stephensi and east-central Ethiopia An. stephensi populations, particularly Jigjiga An. stephensi. Our findings of the insecticide resistance profile, coupled with the likely source population of Fiq An. stephensi, can inform vector control strategies against this malaria vector in Fiq and Jigjiga to limit further spread out of these two locations to other parts of the country and continent.

evolutionary biology↗

bioRxiv2024

Molecular confirmation of Anopheles stephensi in the Al Hudaydah Governorate, Yemen, 2021-2022.

Anopheles stephensi is an invasive malaria vector in Africa. To determine the status of the mosquito in Yemen, An. stephensi vector surveillance and molecular confirmation was conducted in Al Hudaydah Governorate in 2021 and 2022. Mosquito larvae were collected in suspected man-made breeding habitats in Ah Dahi and Zabid city in 2021 and 2022, respectively. Mosquitoes morphologically identified as An. stephensi underwent molecular confirmation through PCR assays, sequencing, and phylogenetic analysis of the cytochrome oxidase subunit I (COI) gene and internal transcribed spacer 2 locus (ITS2). Analysis confirmed An. stephensi identification for the majority of samples (39/41), with two COI haplotypes detected: one newly reported haplotype and one haplotype common to Northeast Ethiopia and Somaliland. No clustering with An. stephensi from the Arabian Peninsula was observed. These findings provide preliminary insight into the diversity of An. stephensi in Yemen and the connection between An. stephensi in Yemen and East Africa.

genetics↗

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↗