Biology subjects

Irish, S. R.

Publications and source records attributed to Irish, S. R..

13 recordsLinked to original sources

bioRxiv2025

Malaria entomological surveillance in Kinshasa Province: A longitudinal study

BackgroundMalaria remains a major public health challenge in the Democratic Republic of Congo. To address the lack of contemporary entomological data, particularly in Kinshasa Province, this four-year study characterized key entomological parameters, including mosquito species composition, abundance, biting behavior, and insecticide resistance. MethodsWe conducted a prospective observational cohort study (2018-2022) in three health areas representing rural, peri-urban, and urban settings in Kinshasa Province. Adult Anopheles mosquitoes were sampled using CDC miniature light traps and pyrethrum spray catches. Insecticide susceptibility of adult females was assessed using WHO tube tests, and a generalized estimating equations model evaluated the effects of year, season, site, sampling location, and collection time on mosquito abundance. ResultsA total of 1,449 Anopheles mosquitoes were collected: 50% in the rural health area of Bu, 49% in peri-urban Kimpoko, and 1% in urban La Voix du Peuple. The species captured were An. gambiae s.l. (85%), An. paludis (11%), and An. funestus (4%). An. gambiae s.l. was significantly more abundant indoors and after 10 PM. The overall entomological inoculation rate (EIR) was 4.6 infective bites per person per year, with An. gambiae s.l. contributing the highest rate. An. paludis showed a localized transmission peak in Impuru during the rainy season (EIR = 8.87). Resistance to DDT and pyrethroids was widespread, with an estimated 0.94 frequency of the kdr L1014F mutation. Bendiocarb and pirimiphos-methyl remained effective. ConclusionsThis study confirms that An. gambiae s.l. remains the predominant malaria vector and plays a central role in transmission in Kinshasa. However, an emerging role of An. paludis in rural settings was observed. These findings underscore the need for vector control strategies tailored to diverse ecological settings. Continued entomological surveillance will be essential to track biting behavior and resistance patterns and ensure that interventions remain effective over time. Author summaryMalaria remains a major health problem in the Democratic Republic of the Congo, but very little recent information is available about the mosquitoes that spread the disease, especially in Kinshasa Province. To help fill this gap, we spent four years studying mosquitoes in rural, peri-urban, and urban communities. We focused on how many mosquitoes were present, which species they were, when and where they bite, and whether they were resistant to the insecticides commonly used in malaria control. We found that most mosquitoes belonged to Anopheles gambiae, the main malaria-transmitting species in Africa. These mosquitoes mostly bit indoors and late at night, when bed nets can offer good protection. However, we also observed mosquitoes biting earlier in the evening and outside, which may reduce the impact of bed nets. Another species, Anopheles paludis, played an important role in malaria transmission in some rural areas, showing that different environments can shape which mosquitoes spread the disease. We also found that many mosquitoes were resistant to widely used insecticides, although some alternative insecticides were still effective. Our findings show why it is important to monitor mosquito behavior and insecticide resistance regularly and to adapt malaria prevention strategies to local conditions.

ecology↗

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↗

bioRxiv2025

Malaria shaped human spatial organisation for the last 74 thousand years

The mechanisms driving the spatial organisation of early human societies in Africa are typically addressed through climate variables 1-3. However, genetic and archaeological studies have also suggested diseases as a major source of selection in the Pleistocene. Here, we explore whether P. falciparum-induced malaria, a major world disease, drove habitat choice in human societies between 74 and 5 thousand years ago (kya). Using species distribution models of three main mosquito complexes with palaeoclimatic reconstructions and combining the results with epidemiological information, we estimated an index of malaria transmission risk in sub-Saharan Africa through time. We then correlated it with an independent reconstruction of the human niche over the same time period and region. Our results show that humans strongly avoided or were unsuccessful in potential malaria hotspots. The effects of these choices shaped human demography for the last 74 kya, and likely much earlier, by fragmenting human societies over time and contributing to the formation of modern population structure. Our results highlight the importance of considering disease distributions when modelling estimates of past human demography, demonstrating that factors beyond climate underlay patterns of human habitat choice, exchange, and dispersal. Sentence summaryMalaria shaped human habitat choice, exchange, and dispersal since the late Pleistocene in sub-Saharan Africa.

evolutionary biology↗

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↗

bioRxiv2024

Cryptic population structure and insecticide resistance in Anopheles gambiae from the southern Democratic Republic of Congo

The Democratic Republic of Congo (DRC) suffers from one of the highest malaria burdens worldwide, but information on its Anopheles vector populations is relatively limited. Preventative malaria control in DRC is reliant on pyrethroid-treated nets, raising concerns over the potential impacts of insecticide resistance. We sampled Anopheles gambiae from three geographically distinct populations (Kimpese, Kapolowe and Mikalayi) in southern DRC, collecting from three sub-sites per population and characterising mosquito collections from each for resistance to pyrethroids using WHO tube bioassays. Resistance to each of three different pyrethroids was generally high in An. gambiae with <92% mortality in all tests, but varied between collections, with mosquitoes from Kimpese being the most resistant. Whole genome sequencing of 165 An. gambiae revealed evidence for genetic differentiation between Kimpese and Kapolowe / Mikalayi, but not between the latter two sample sites despite separation of approximately 800km. Surprisingly, there was evidence of population structure at a small spatial scale between collection subsites in Kimpese, despite separation of just tens of kilometres. Intra-population (H12) and inter-population (FST) genome scans identified multiple peaks corresponding to genes associated with insecticide resistance such as the voltage gated sodium channel (Vgsc) target site on chromosome 2L, a Cyp6 cytochrome P450 cluster on chromosome arm 2R, and the Cyp9k1 P450 gene on chromosome X. In addition, in the Kimpese subsites, the P450 redox partner gene Cpr showed evidence for contemporary selection (H12) and population differentiation (FST) meriting further exploration as a potential resistance associated marker.

evolutionary biology↗

bioRxiv2021

Using marine cargo traffic to identify countries in Africa with greatest risk of invasion by Anopheles stephensi

Anopheles stephensi is an efficient malaria vector commonly found in South Asia and the Arabian Peninsula, but in recent years it has established as an invasive species in the Horn of Africa (HoA). In this region, An. stephensi was first detected in a livestock quarantine station near a major seaport in Djibouti in 2012, in Ethiopia in 2016, in Sudan in 2018 and Somalia in 2019. Anopheles stephensi often uses artificial containers as larval habitats, which may facilitate introduction through maritime trade as has been seen with other invasive container breeding mosquitoes. If An. stephensi is being introduced through maritime traffic, prioritization exercises are needed to identify locations at greatest risk of An. stephensi introduction for early detection and rapid response, limiting further invasion opportunities. Here, we use UNCTAD maritime trade data to 1) identify coastal African countries which were most highly connected to select An. stephensi endemic countries in 2011, prior to initial detection in Africa, 2) develop a ranked prioritization list of countries based on likelihood of An. stephensi introduction for 2016 and 2020 based on maritime trade alone and maritime trade and habitat suitability, and 3) use network analysis to describe intracontinental maritime trade and eigenvector centrality to determine likely paths of further introduction on the continent if An. stephensi is detected in a new location. Our results show that in 2011, Sudan and Djibouti were ranked as the top two countries with likelihood of An. stephensi introduction based on maritime trade alone, and these were indeed the first two coastal countries in the HoA where An. stephensi was detected. Trade data from 2020 with Djibouti and Sudan included as source populations identify Egypt, Kenya, Mauritius, Tanzania, and Morocco as the top five countries with likelihood of An. stephensi introduction. When factoring in habitat suitability, Egypt, Kenya, Tanzania, Morocco, and Libya are ranked highest. Network analysis revealed that the countries with the highest eigenvector centrality scores, and therefore highest degrees of connectivity with other coastal African nations were South Africa (0.175), Mauritius (0.159), Ghana (0.159), Togo (0.157), and Morocco (0.044) and therefore detection of An. stephensi in any one of these locations has a higher potential to cascade further across the continent via maritime trade than those with lower eigenvector centrality scores. Taken together, these data could serve as tools to prioritize efforts for An. stephensi surveillance and control in Africa. Surveillance in seaports of countries at greatest risk of introduction may serve as an early warning system for the detection of An. stephensi, providing opportunities to limit further introduction and expansion of this invasive malaria vector in Africa.

ecology↗

bioRxiv2021

Insecticide susceptibility of Aedes (Stegomyia) aegypti (Linnaeus, 1762) and Aedes (Stegomyia) albopictus (Skuse, 1894) in Kinshasa, Democratic Republic of the Congo

Aedes aegypti and Aedes albopictus are arbovirus vectors of public health concern. Although the Democratic Republic of the Congo (DRC) faces a long-standing risk of Aedes-borne viruses, data on insecticide resistance of Aedes populations are absent. To address this gap, we investigated insecticide susceptibility of Ae. aegypti and Ae. albopictus in areas with a high risk of arbovirus transmission. We also investigated the frequency of knock-down resistance (kdr) mutations in Ae. aegypti. Immature stages of Ae. aegypti and Ae. albopictus were collected from two sites in Kinshasa (Lingwala and Cite Verte) between April and July 2017 and reared to the adult stage. Wild-caught adult Ae. aegypti were collected in 2016 in another site (Ngaliema). Female Ae. aegypti (from Lingwala) and Ae. albopictus (from Cite Verte) were used in WHO tube insecticide susceptibility tests. The F1534C, V1016I and V410L kdr mutations were genotyped in Ae. aegypti from Lingwala and Ngaliema. We observed Ae. aegypti to be susceptible to bendiocarb, propoxur and malathion, suspected resistant to permethrin, and resistant to deltamethrin and DDT. Aedes albopictus was susceptible to bendiocarb, propoxur, malathion and permethrin, suspected resistant to deltamethrin and resistant to DDT. While F1534C and V1016I were not detected, a few Ae. aegypti from Lingwala were heterozygous for the mutation V410L. This study reports for the first time the insecticide resistance status of Aedes spp. and the detection of the kdr mutation V410L in Ae. aegypti in DRC. Given the resistance profile, carbamates and potentially malathion are recommended insecticide options against Ae. aegypti in Kinshasa. It will be important to develop Aedes control strategies based on the resistance patterns of Aedes in Kinshasa.

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↗

bioRxiv2021

High-throughput Identification of Eukaryotic Parasites and Arboviruses in Mosquitoes

Vector-borne pathogens cause many human infectious diseases and are responsible for high mortality and morbidity throughout the world. They can also cause livestock epidemics with dramatic social and economic consequences. Due to the high costs, vector-borne disease surveillance is often limited to current threats, and the investigation of emerging pathogens typically occur after the reports of clinical cases. Here, we use high-throughput sequencing to detect and identify a wide range of parasites and viruses carried by mosquitoes from Cambodia, Guinea, Mali and Maryland. We apply this approach to individual Anopheles mosquitoes as well as pools of mosquitoes captured in traps; and compare the outcomes of this assay when applied to DNA or RNA. We identified known human and animal pathogens and mosquito parasites belonging to a wide range of taxa, insect Flaviviruses, and novel DNA sequences from previously uncharacterized organisms. Our results also revealed that analysis of the content of an entire trap is an efficient approach to monitor and identify potential vector-borne pathogens in large surveillance studies, and that analyses of RNA extracted from mosquitoes is preferable, when possible, over DNA-based analyses. Overall, we describe a flexible and easy-to-customize assay that can provide important information for vector-borne disease surveillance and research studies to efficiently complement current approaches.

microbiology↗

bioRxiv2020

Reduced long-lasting insecticidal net efficacy and pyrethroid insecticide resistance are associated with over-expression of CYP6P4, CYP6P3 and CYP6Z1 in populations of Anopheles coluzzii from South-East Cote d Ivoire

BackgroundResistance to major public health insecticides in Cote dIvoire has intensified and now threatens the long-term effectiveness of malaria vector control interventions. MethodsThis study evaluated the bioefficacy of conventional and next-generation long-lasting insecticidal nets (LLINs), determined resistance profiles, and characterized molecular and metabolic mechanisms in wild Anopheles coluzzii from South-East Cote dIvoire in 2019. ResultsPhenotypic resistance was intense: more than 25% of mosquitoes survived exposure to ten times the doses of pyrethroids required to kill susceptible populations. Similarly, 24-hour mortality to deltamethrin-only LLINs was very low and not significantly different to an untreated net. Sub-lethal pyrethroid exposure did not induce significant delayed vector mortality 72 hours later. In contrast, LLINs containing the synergist piperonyl butoxide (PBO), or new insecticides, clothianidin and chlorfenapyr, were highly toxic to An. coluzzii. Pyrethroid-susceptible An. coluzzii were significantly more likely to be infected with malaria, compared to those that survived insecticidal exposure. Pyrethroid resistance was associated with significant over-expression of CYP6P4, CPY6Z1 and CYP6P3. ConclusionsStudy findings raise concerns regarding the operational failure of standard LLINs and support the urgent deployment of vector control interventions incorporating PBO, chlorfenapyr or clothianidin in areas of high resistance intensity in Cote dIvoire.

genetics↗

bioRxiv2020

Insecticide resistance status of Aedes aegypti in Bangladesh

BackgroundArboviral 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. MethodsAedes 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. ResultsHigh 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. ConclusionsThe 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.

microbiology↗

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

Characterizing the molecular and metabolic mechanisms of insecticide resistance in Anopheles gambiae s.l. in Faranah, Guinea

BackgroundIn recent years, the scale-up of long-lasting insecticidal nets (LLINs) and indoor residual spraying (IRS) has greatly reduced malaria transmission. However, malaria remains a global public health concern with the majority of disease burden in sub-Saharan Africa. Insecticide resistance is a growing problem among Anopheles vector populations, with potential implications for the continued effectiveness of available control interventions. Improved understanding of current resistance levels and underlying mechanisms is essential to design appropriate management strategies and to mitigate future selection for resistance.\n\nMethodsAnopheles gambiae s.l. mosquitoes were collected from three villages in Faranah Prefecture, Guinea and their levels of susceptibility to seven insecticides were measured using CDC resistance intensity bioassays. Synergist assays with piperonyl butoxide (PBO) were also undertaken to assess the role of elevated mixed-function oxidases in resistance. RNA was extracted from 563 individuals and PCR was performed on cDNA to determine vector species, presence of target site mutations (L1014F kdr, N1575Y and G119S Ace-1), Plasmodium falciparum infection, and relative expression of three metabolic genes (CYP6M2, CYP6P3 and GSTD3).\n\nResultsIn Faranah, resistance to permethrin and deltamethrin was observed, as well as possible resistance to bendiocarb. All assayed vector populations were fully susceptible to alpha-cypermethrin, pirimiphos-methyl, clothianidin and chlorfenapyr. Plasmodium falciparum infection was detected in 7.3% (37/508) mosquitoes tested. The L1014F kdr mutation was found in 100% of a sub-sample of 60 mosquitoes, supporting its fixation in the region. The N1575Y mutation was identified in 20% (113/561) of individuals, with ongoing selection evidenced by significant deviations from Hardy-Weinberg equilibrium. The G119S Ace-1 mutation was detected in 62.1% (18/29) of mosquitoes tested and was highly predictive of bendiocarb bioassay survival. The metabolic resistance genes, CYP6M2, CYP6P3 and GSTD3, were found to be overexpressed in wild resistant and susceptible An. gambiae s.s. populations, compared to a susceptible G3 colony. Furthermore, CYP6P3 was significantly overexpressed in bendiocarb survivors, implicating its potential role in carbamate resistance in Faranah.\n\nConclusionsIdentification of intense resistance to permethrin and deltamethrin in Faranah, is of concern, as the Guinea National Malaria Control Program (NMCP) relies exclusively on the distribution of pyrethroid-treated LLINs for vector control. Study findings will be used to guide current and future control strategies in the region.

genetics↗