Corticosteroid Treatment During Sepsis Alters Hippocampal Function in Male and Female Survivors.

Background: Millions of sepsis survivors annually face neuropsychiatric sequelae of their illness. Corticosteroids are frequently administered for sepsis, and their use improves neuropsychiatric outcomes, but the mechanisms are unknown. In light of prior work that has shown persistent inflammation in sepsis survivors, we hypothesized that short-term corticosteroid treatment during illness would reverse the long-term impact of sepsis on inflammatory gene expression in the hippocampus and rescue associated changes to affective behaviors. Methods: Male and female mice underwent cecal ligation and puncture or a sham surgery to induce acute infection and were treated for 5 days with corticosterone or vehicle. Starting 2 weeks after the surgery, we performed functional phenotyping in the survivor mice followed by hippocampal RNA sequencing to identify underlying mechanisms. Results: Long-term cecal ligation and puncture survivors exhibited anxiety-like behavior, increased central hypothalamic-pituitary-adrenal axis activity, and persistent systemic and neuroinflammation. Corticosterone treatment during illness did not reverse anxiety-like behavior or inflammation in survivors. Instead, corticosterone treatment impaired object memory and increased active coping behavior in females. History of corticosterone treatment influenced the expression of >10% of detectable transcripts in the dorsal and ventral hippocampus, including a coordinated downregulation of activity-dependent genes. Conclusions: Corticosterone treatment during sepsis impaired memory formation in survivors and caused a lasting decrease in hippocampal neural activity, which could underlie its effect on memory. Future studies should focus on how this lasting effect of corticosteroid treatment on hippocampal activity and memory translates into improved neuropsychiatric outcomes in human sepsis survivors.

Field-based assessments of the seasonality of Culex pipiens sensu lato in England: an important enzootic vector of Usutu and West Nile viruses.

BACKGROUND: Usutu virus (USUV), which is closely related to West Nile virus (WNV), sharing a similar ecology and transmission cycle, was first reported in the UK in the southeast of England in 2020. Both USUV and WNV are emerging zoonotic viruses hosted by wild birds. The 2020 finding of USUV in England raised awareness of this virus and highlighted the importance of understanding the seasonality of Culex pipiens sensu lato (Cx. pipiens s.l.), the main enzootic vector of these viruses. Zoos are prime locations for trapping mosquitoes because of their infrastructure, security, and range of vertebrate hosts and aquatic habitats. METHODS: Three independent zoo-based case studies at four locations that cover the seasonality of Cx. pipiens s.l. in England were undertaken: (i) London Zoo (Zoological Society London [ZSL]) and surrounding areas, London; (ii) Chester Zoo (Cheshire); (ii) Twycross Zoo (Leicestershire); and (iv) Flamingo Land (zoo; North Yorkshire). Various adult mosquito traps were used to catch adult Cx. pipiens s.l. across seasons. RESULTS: High yields of Cx. pipiens s.l./Culex torrentium were observed in Biogents-Mosquitaire and Center for Disease Control and Prevention Gravid traps in all studies where these traps were used. Mosquito counts varied between sites and between years. Observations of adult Cx. pipiens s.l./Cx. torrentium abundance and modelling studies demonstrated peak adult abundance between late July and early August, with active adult female Cx. pipiens s.l./Cx. torrentium populations between May and September. CONCLUSIONS: The information collated in this study illustrates the value of multiple mosquito monitoring approaches in zoos to describe the seasonality of this UK vector across multiple sites in England and provides a framework that can be used for ongoing and future surveillance programmes and disease risk management strategies.

Corticosterone enhances formation of non-fear but not fear memory during infectious illness.

Introduction: Survivors of critical illness are at high risk of developing post-traumatic stress disorder (PTSD) but administration of glucocorticoids during the illness can lower that risk. The mechanism is not known but may involve glucocorticoid modulation of hippocampal- and amygdala-dependent memory formation. In this study, we sought to determine whether glucocorticoids given during an acute illness influence the formation and persistence of fear and non-fear memories from the time of the illness. Methods: We performed cecal ligation and puncture in male and female mice to induce an acute infectious illness. During the illness, mice were introduced to a neutral object in their home cage and separately underwent contextual fear conditioning. We then tested the persistence of object and fear memories after recovery. Results: Glucocorticoid treatment enhanced object discrimination but did not alter the expression of contextual fear memory. During context re-exposure, neural activity was elevated in the dentate gyrus irrespective of fear conditioning. Conclusions: Our results suggest that glucocorticoids given during illness enhance hippocampal-dependent non-fear memory processes. This indicates that PTSD outcomes in critically ill patients may be improved by enhancing non-fear memories from the time of their illness.

Corticosterone enhances formation of non-fear but not fear memory during infectious illness.

Survivors of critical illness are at high risk of developing post-traumatic stress disorder (PTSD) but administration of glucocorticoids during the illness can lower that risk. The mechanism is not known but may involve glucocorticoid modulation of hippocampal- and amygdalar-dependent memory formation. In this study, we sought to determine whether glucocorticoids given during an acute illness influence the formation and persistence of fear and non-fear memories from the time of the illness. We performed cecal ligation and puncture in male and female mice to induce an acute infectious illness. During the illness, mice were introduced to a neutral object in their home cage and separately underwent contextual fear conditioning. We then tested the persistence of object and fear memories after recovery. Glucocorticoid treatment enhanced object discrimination but did not alter the expression of contextual fear memory. During context re-exposure, neural activity was elevated in the dentate gyrus irrespective of fear conditioning. Our results suggest that glucocorticoids given during illness enhance hippocampal-dependent non-fear memory processes. This indicates that PTSD outcomes in critically ill patients may be improved by enhancing non-fear memories from the time of their illness.

Direct Evidence of the Exfoliation Efficiency and Graphene Dispersibility of Green Solvents toward Sustainable Graphene Production.

Achieving a sustainable production of pristine high-quality graphene and other layered materials at a low cost is one of the bottlenecks that needs to be overcome for reaching 2D material applications at a large scale. Liquid phase exfoliation in conjunction with N-methyl-2-pyrrolidone (NMP) is recognized as the most efficient method for both the exfoliation and dispersion of graphene. Unfortunately, NMP is neither sustainable nor suitable for up-scaling production due to its adverse impact on the environment. Here, we show the real potential of green solvents by revealing the independent contributions of their exfoliation efficiency and graphene dispersibility to the graphene yield. By experimentally separating these two factors, we demonstrate that the exfoliation efficiency of a given solvent is independent of its dispersibility. Our studies revealed that isopropanol can be used to exfoliate graphite as efficiently as NMP. Our finding is corroborated by the matching ratio between the polar and dispersive energies of graphite and that of the solvent surface tension. This direct evidence of exfoliation efficiency and dispersibility of solvents paves the way to developing a deeper understanding of the real potential of sustainable graphene manufacturing at a large scale.

Mapping and monitoring tick (Acari, Ixodida) distribution, seasonality, and host associations in the United Kingdom between 2017 and 2020.

Tick-borne disease risk is intrinsically linked to the distribution of tick vector species. To assess risk and anticipate disease emergence, an understanding of tick distribution, host associations, and seasonality is needed. This can be achieved, to some extent, using passive surveillance supported by engagement with the public, animal health, and public health experts. The Tick Surveillance Scheme (TSS) collects data and maps tick distribution across the United Kingdom (UK). Between 2017 and 2020, 3720 tick records were received and 39 tick species were detected. Most records were acquired in the UK, with a subset associated with recent overseas travel. The dominant UK acquired species was Ixodes ricinus (Ixodida: Ixodidae, Linnaeus), the main vector of Lyme borreliosis. Records peaked during May and June, highlighting a key risk period for tick bites. Other key UK species were detected, including Dermacentor reticulatus (Ixodida: Ixodidae, Fabricius) and Haemaphysalis punctata (Ixodida: Ixodidae, Canestrini & Fanzago) as well as several rarer species that may present novel tick-borne disease risk to humans and other animals. Updated tick distribution maps highlight areas in the UK where tick exposure has occurred. There is evidence of increasing human tick exposure over time, including during the COVID-19 pandemic, but seasonal patterns remain unchanged.

Forebrain Glucocorticoid Receptor Overexpression Alters Behavioral Encoding of Hippocampal CA1 Pyramidal Cells in Mice.

Glucocorticoid signaling influences hippocampal-dependent behavior and vulnerability to stress-related neuropsychiatric disorders. In mice, lifelong overexpression of glucocorticoid receptor (GR) in forebrain excitatory neurons altered exploratory behavior, cognition, and dorsal hippocampal gene expression in adulthood, but whether GR overexpression alters the information encoded by hippocampal neurons is not known. We performed in vivo microendoscopic calcium imaging of 1359 dorsal CA1 pyramidal cells in freely behaving male and female wild-type (WT) and GR-overexpressing (GRov) mice during exploration of a novel open field, where most CA1 neurons are expected to respond to center location and mobility. Most neurons showed sensitivity to center location and/or mobility based on single-neuron calcium amplitude and event rate, but these sensitivity patterns differed between genotypes. GRov neurons were more likely than WT neurons to display center sensitivity and less likely to display mobility sensitivity. More than one-third of these responsive GRov neurons were sensitive only to center location and not mobility, while uniquely center-sensitive neurons were rare in WT. Most center-sensitive neurons exhibited anticipatory activity, suggesting they could drive behavior. We conclude that, compared with wild-type, dorsal CA1 pyramidal cells in GRov mice preferentially respond to center location rather than mobility in a novel open field. Such changes in the information encoded by individual hippocampal neurons in an aversive environment could underlie changes in stress vulnerability because of genetic or epigenetic variations in glucocorticoid receptor signaling.

Evidence for overwintering and autochthonous transmission of Usutu virus to wild birds following its redetection in the United Kingdom.

Usutu virus (USUV) is an emerging zoonotic arbovirus in Europe, where it primarily impacts Eurasian blackbirds (Turdus merula). For mosquito-borne viruses to persist in temperate areas, transovarial transmission in vectors or overwintering in either hosts or diapausing vectors must occur to facilitate autochthonous transmission. We undertook surveillance of hosts and vectors in 2021 to elucidate whether USUV had overwintered in the United Kingdom (UK) following its initial detection there in 2020. From 175 dead bird submissions, we detected 1 case of USUV infection, in a blackbird, from which a full USUV genome was derived. Using a molecular clock analysis, we demonstrate that the 2021 detection shared a most recent common ancestor with the 2020 Greater London, UK, USUV sequence. In addition, we identified USUV-specific neutralizing antibodies in 10 out of 86 serum samples taken from captive birds at the index site, demonstrating in situ cryptic infection and potential sustained transmission. However, from 4966 mosquitoes, we detected no USUV RNA suggesting that prevalence in the vector community was absent or low during sampling. Combined, these results suggest that USUV overwintered in the UK, thus providing empirical evidence for the continued northward expansion of this vector-borne viral disease. Currently, our detection indicates geographically restricted virus persistence. Further detections over time will be required to demonstrate long-term establishment. It remains unclear whether the UK, and by extension other high-latitude regions, can support endemic USUV infection.

Correction: Peters et al. Benchmarking the ACEnano Toolbox for Characterisation of Nanoparticle Size and Concentration by Interlaboratory Comparison. Molecules 2021, 26, 5315.

Due to miscommunication a number of potential co-authors were not listed in the original publication [...].

Combining host and vector data informs emergence and potential impact of an Usutu virus outbreak in UK wild birds.

Following the first detection in the United Kingdom of Usutu virus (USUV) in wild birds in 2020, we undertook a multidisciplinary investigation that combined screening host and vector populations with interrogation of national citizen science monitoring datasets to assess the potential for population impacts on avian hosts. Pathological findings from six USUV-positive wild passerines were non-specific, highlighting the need for molecular and immunohistochemical examinations to confirm infection. Mosquito surveillance at the index site identified USUV RNA in Culex pipiens s.l. following the outbreak. Although the Eurasian blackbird (Turdus merula) is most frequently impacted by USUV in Europe, national syndromic surveillance failed to detect any increase in occurrence of clinical signs consistent with USUV infection in this species. Furthermore, there was no increase in recoveries of dead blackbirds marked by the national ringing scheme. However, there was regional clustering of blackbird disease incident reports centred near the index site in 2020 and a contemporaneous marked reduction in the frequency with which blackbirds were recorded in gardens in this area, consistent with a hypothesis of disease-mediated population decline. Combining results from multidisciplinary schemes, as we have done, in real-time offers a model for the detection and impact assessment of future disease emergence events.

Development and validation of multivariable machine learning algorithms to predict risk of cancer in symptomatic patients referred urgently from primary care: a diagnostic accuracy study.

OBJECTIVES: To develop and validate tests to assess the risk of any cancer for patients referred to the NHS Urgent Suspected Cancer (2-week wait, 2WW) clinical pathways. SETTING: Primary and secondary care, one participating regional centre. PARTICIPANTS: Retrospective analysis of data from 371 799 consecutive 2WW referrals in the Leeds region from 2011 to 2019. The development cohort was composed of 224 669 consecutive patients with an urgent suspected cancer referral in Leeds between January 2011 and December 2016. The diagnostic algorithms developed were then externally validated on a similar consecutive sample of 147 130 patients (between January 2017 and December 2019). All such patients over the age of 18 with a minimum set of blood counts and biochemistry measurements available were included in the cohort. PRIMARY AND SECONDARY OUTCOME MEASURES: sensitivity, specificity, negative predictive value, positive predictive value, Receiver Operating Characteristic (ROC) curve Area Under Curve (AUC), calibration curves RESULTS: We present results for two clinical use-cases. In use-case 1, the algorithms identify 20% of patients who do not have cancer and may not need an urgent 2WW referral. In use-case 2, they identify 90% of cancer cases with a high probability of cancer that could be prioritised for review. CONCLUSIONS: Combining a panel of widely available blood markers produces effective blood tests for cancer for NHS 2WW patients. The tests are affordable, and can be deployed rapidly to any NHS pathology laboratory with no additional hardware requirements.

Postradioiodine Graves' management: The PRAGMA study.

OBJECTIVE: Thyroid status in the months following radioiodine (RI) treatment for Graves' disease can be unstable. Our objective was to quantify frequency of abnormal thyroid function post-RI and compare effectiveness of common management strategies. DESIGN: Retrospective, multicentre and observational study. PATIENTS: Adult patients with Graves' disease treated with RI with 12 months' follow-up. MEASUREMENTS: Euthyroidism was defined as both serum thyrotropin (thyroid-stimulating hormone [TSH]) and free thyroxine (FT4) within their reference ranges or, when only one was available, it was within its reference range; hypothyroidism as TSH ≥ 10 mU/L, or subnormal FT4 regardless of TSH; hyperthyroidism as TSH below and FT4 above their reference ranges; dysthyroidism as the sum of hypo- and hyperthyroidism; subclinical hypothyroidism as normal FT4 and TSH between the upper limit of normal and <10 mU/L; and subclinical hyperthyroidism as low TSH and normal FT4. RESULTS: Of 812 patients studied post-RI, hypothyroidism occurred in 80.7% and hyperthyroidism in 48.6% of patients. Three principal post-RI management strategies were employed: (a) antithyroid drugs alone, (b) levothyroxine alone, and (c) combination of the two. Differences among these were small. Adherence to national guidelines regarding monitoring thyroid function in the first 6 months was low (21.4%-28.7%). No negative outcomes (new-onset/exacerbation of Graves' orbitopathy, weight gain, and cardiovascular events) were associated with dysthyroidism. There were significant differences in demographics, clinical practice, and thyroid status postradioiodine between centres. CONCLUSIONS: Dysthyroidism in the 12 months post-RI was common. Differences between post-RI strategies were small, suggesting these interventions alone are unlikely to address the high frequency of dysthyroidism.

UV-Vis Spectroscopic Characterization of Nanomaterials in Aqueous Media.

The physicochemical characterization of nanomaterials (NMs) is often an analytical challenge, due to their small size (at least one dimension in the nanoscale, i.e. 1-100 nm), dynamic nature, and diverse properties. At the same time, reliable and repeatable characterization is paramount to ensure safety and quality in the manufacturing of NM-bearing products. There are several methods available to monitor and achieve reliable measurement of nanoscale-related properties, one example of which is Ultraviolet-Visible Spectroscopy (UV-Vis). This is a well-established, simple, and inexpensive technique that provides non-invasive and fast real-time screening evaluation of NM size, concentration, and aggregation state. Such features make UV-Vis an ideal methodology to assess the proficiency testing schemes (PTS) of a validated standard operating procedure (SOP) intended to evaluate the performance and reproducibility of a characterization method. In this paper, the PTS of six partner laboratories from the H2020 project ACEnano were assessed through an interlaboratory comparison (ILC). Standard gold (Au) colloid suspensions of different sizes (ranging 5-100 nm) were characterized by UV-Vis at the different institutions to develop an implementable and robust protocol for NM size characterization.

Benchmarking the ACEnano Toolbox for Characterisation of Nanoparticle Size and Concentration by Interlaboratory Comparisons.

ACEnano is an EU-funded project which aims at developing, optimising and validating methods for the detection and characterisation of nanomaterials (NMs) in increasingly complex matrices to improve confidence in the results and support their use in regulation. Within this project, several interlaboratory comparisons (ILCs) for the determination of particle size and concentration have been organised to benchmark existing analytical methods. In this paper the results of a number of these ILCs for the characterisation of NMs are presented and discussed. The results of the analyses of pristine well-defined particles such as 60 nm Au NMs in a simple aqueous suspension showed that laboratories are well capable of determining the sizes of these particles. The analysis of particles in complex matrices or formulations such as consumer products resulted in larger variations in particle sizes within technologies and clear differences in capability between techniques. Sunscreen lotion sample analysis by laboratories using spICP-MS and TEM/SEM identified and confirmed the TiO2 particles as being nanoscale and compliant with the EU definition of an NM for regulatory purposes. In a toothpaste sample orthogonal results by PTA, spICP-MS and TEM/SEM agreed and stated the TiO2 particles as not fitting the EU definition of an NM. In general, from the results of these ILCs we conclude that laboratories are well capable of determining particle sizes of NM, even in fairly complex formulations.

Gonadectomy in conditions affecting sex development: a registry-based cohort study.

OBJECTIVES: To determine trends in clinical practice for individuals with DSD requiring gonadectomy. DESIGN: Retrospective cohort study. METHODS: Information regarding age at gonadectomy according to diagnosis; reported sex; time of presentation to specialist centre; and location of centre from cases reported to the International DSD Registry and who were over 16 years old in January 2019. RESULTS: Data regarding gonadectomy were available in 668 (88%) individuals from 44 centres. Of these, 248 (37%) (median age (range) 24 (17, 75) years) were male and 420 (63%) (median age (range) 26 (16, 86) years) were female. Gonadectomy was reported from 36 centres in 351/668 cases (53%). Females were more likely to undergo gonadectomy (n = 311, P < 0.0001). The indication for gonadectomy was reported in 268 (76%). The most common indication was mitigation of tumour risk in 172 (64%). Variations in the practice of gonadectomy were observed; of the 351 cases from 36 centres, 17 (5%) at 9 centres had undergone gonadectomy before their first presentation to the specialist centre. Median age at gonadectomy of cases from high-income countries and low-/middle-income countries (LMIC) was 13.0 years (0.1, 68) years and 16.5 years (1, 28), respectively (P < 0.0001) with the likelihood of long-term retention of gonads being higher in LMIC countries. CONCLUSIONS: The likelihood of gonadectomy depends on the underlying diagnosis, sex of rearing and the geographical setting. Clinical benchmarks, which can be studied across all forms of DSD will allow a better understanding of the variation in the practice of gonadectomy.

Nanoparticle Tracking Analysis of Gold Nanoparticles in Aqueous Media through an Inter-Laboratory Comparison.

In the field of nanotechnology, analytical characterization plays a vital role in understanding the behavior and toxicity of nanomaterials (NMs). Characterization needs to be thorough and the technique chosen should be well-suited to the property to be determined, the material being analyzed and the medium in which it is present. Furthermore, the instrument operation and methodology need to be well-developed and clearly understood by the user to avoid data collection errors. Any discrepancies in the applied method or procedure can lead to differences and poor reproducibility of obtained data. This paper aims to clarify the method to measure the hydrodynamic diameter of gold nanoparticles by means of Nanoparticle Tracking Analysis (NTA). This study was carried out as an inter-laboratory comparison (ILC) amongst seven different laboratories to validate the standard operating procedure's performance and reproducibility. The results obtained from this ILC study reveal the importance and benefits of detailed standard operating procedures (SOPs), best practice updates, user knowledge, and measurement automation.

Working towards a Co-Ordinated Approach to Invasive Mosquito Detection, Response and Control in the UK.

The United Kingdom (UK) has reported a single detection of the eggs of the invasive mosquito vector Aedes albopictus in each of the three years from 2016 to 2018, all in southeast England. Here, we report the detection of mosquito eggs on three occasions at two sites in London and southeast England in September 2019. Mosquito traps were deployed at 56 sites, in England, Scotland, Wales, and Northern Ireland, as part of a coordinated surveillance programme with local authorities, Edge Hill University, and government departments. Response to each detection was coordinated by Public Health England's (PHE) local health protection teams, with technical support from PHE's Medical Entomology group, and control conducted by the respective local authority. Control, including source reduction and larviciding, was conducted within a 300 metre radius of the positive site. The response followed a National Contingency Plan for Invasive Mosquitoes: Detection of Incursions. Although the response to these incidents was rapid and well co-ordinated, recommendations are made to further develop mosquito surveillance and control capability for the UK.

Microbial Ecology of Atlantic Salmon (Salmo salar) Hatcheries: Impacts of the Built Environment on Fish Mucosal Microbiota.

Successful rearing of fish in hatcheries is critical for conservation, recreational fishing, commercial fishing through wild stock enhancements, and aquaculture production. Flowthrough (FT) hatcheries require more water than recirculating aquaculture systems (RAS), which enable up to 99% of their water to be recycled, thus significantly reducing environmental impacts. Here, we evaluated the biological and physical microbiome interactions of three Atlantic salmon hatcheries (RAS n = 2, FT n = 1). Gill, skin, and digesta from six juvenile fish along with tank biofilms and water were sampled from tanks in each of the hatcheries (60 fish across 10 tanks) to assess the built environment and mucosal microbiota using 16S rRNA gene sequencing. The water and tank biofilm had more microbial richness than fish mucus, while skin and digesta from RAS fish had 2 times the richness of FT fish. Body sites each had unique microbiomes (P < 0.001) and were influenced by hatchery system type (P < 0.001), with RAS being more similar. A strong association between the tank and fish microbiome was observed. Water and tank biofilm richness was positively correlated with skin and digesta richness. Strikingly, the gill, skin, and digesta communities were more similar to that in the origin tank biofilm than those in all other experimental tanks, suggesting that the tank biofilm has a direct influence on fish-associated microbial communities. Lastly, microbial diversity and mucous cell density were positively associated with fish growth and length. The results from this study provide evidence for a link between the tank microbiome and the fish microbiome, with the skin microbiome as an important intermediate.IMPORTANCE Atlantic salmon, Salmo salar, is the most farmed marine fish worldwide, with an annual production of 2,248 million metric tons in 2016. Salmon hatcheries are increasingly changing from flowthrough toward recirculating aquaculture system (RAS) design to accommodate more control over production along with improved environmental sustainability due to lower impacts on water consumption. To date, microbiome studies of hatcheries have focused either on the fish mucosal microbiota or on the built environment microbiota but have not combined the two to understand their interactions. Our study evaluates how the water and tank biofilm microbiota influences the fish microbiota across three mucosal environments (gill, skin, and digesta). Results from this study highlight how the built environment is a unique source of microbes to colonize fish mucus and, furthermore, how this can influence fish health. Further studies can use this knowledge to engineer built environments to modulate fish microbiota for beneficial phenotypes.

A survey of Anopheles species composition and insecticide resistance on the island of Bubaque, Bijagos Archipelago, Guinea-Bissau.

BACKGROUND: Bubaque is the most populous island of the Bijagos archipelago, a group of malaria-endemic islands situated off the coast of Guinea-Bissau, West Africa. Malaria vector control on Bubaque relies almost exclusively on the use of long-lasting insecticidal nets (LLINs). However, there is little information on local vector bionomics and insecticide resistance. METHODS: A survey of mosquito species composition was performed at the onset of the wet season (June/July) and the beginning of the dry season (November/December). Sampling was performed using indoor adult light-traps and larval dipping. Anopheles mosquitoes were identified to species level and assessed for kdr allele frequency by TaqMan PCR. Females were analysed for sporozoite positivity by CSP-ELISA. Resistance to permethrin and α-cypermethrin was measured using the CDC-bottle bioassay incorporating the synergist piperonyl-butoxide. RESULTS: Several Anopheles species were found on the island, all belonging to the Anopheles gambiae sensu lato (s.l.) complex, including An. gambiae sensu stricto, Anopheles coluzzii, Anopheles melas, and An. gambiae/An. coluzzii hybrids. Endophagic Anopheles species composition and abundance showed strong seasonal variation, with a majority of An. gambiae (50% of adults collected) caught in June/July, while An. melas was dominant in November/December (83.9% of adults collected). Anopheles gambiae had the highest sporozoite rate in both seasons, with infection rates of 13.9% and 20% in June/July and November/December, respectively. Moderate frequencies of the West African kdr allele were found in An. gambiae (36%), An. coluzzii (35%), An. gambiae/An. coluzzii hybrids (42%). Bioassays suggest moderate resistance to α-cypermethrin, but full susceptibility to permethrin. CONCLUSIONS: The island of Bubaque maintained an An. gambiae s.l. population in both June/July and November/December. Anopheles gambiae was the primary vector at the onset of the wet season, while An. melas is likely to be responsible for most dry season transmission. There was moderate kdr allele frequency and synergist assays suggest likely metabolic resistance, which could reduce the efficacy of LLINs. Future control of malaria on the islands should consider the seasonal shift in mosquito species, and should employ continuous monitoring for insecticide resistance.