Cinétique d'accumulation et rétention d'espèces du mercure chez l'étoile de mer Leptasterias polaris: une expérience de transfert trophique à long terme

Dans le cadre de travaux sur le rôle des échinodermes dans le cycle biogéochimique de certains métaux traces en milieu côtier, une étude de l'accumulation et de la rétention d'espèces chimiques du mercure a été menée avec l'étoile de mer Leptasterias polaris sur une période de 40 jours. Les étoiles de mer ont été divisées en deux groupes et nourries avec des moules contaminées soit au méthylmercure (MeHg) (14 mg.kg-1), soit au mercure inorganique (13 mg.kg-1). Les résultats montrent une vitesse d'accumulation dans le système digestif de 0,22 mg.kg-1.j-1 pour le Hg inorganique et 0,17 mg.kg-1.j-1 pour le MeHg. Ces vitesses sont 10 à 15 fois moins importantes dans les gonades et l'endosquelette. Pour le Hg inorganique, la charge relative dans les différents organes analysés se fixe après quelques jours et demeure stable jusqu'à la fin de l'expérience. Pour le MeHg, au contraire, cette charge relative passe progressivement du système digestif vers les gonades et l'exosquelette tout au long de l'expérience. Le pourcentage de rétention (%) demeure constant pour le Hg inorganique (51 ± 13%) mais il augmente régulièrement pour le MeHg, atteignant 90-95% vers la fin de l'exposition. L'application d'un modèle cinétique simple, basé sur un processus d'échange ionique, a permis de calculer des constantes de vitesse d'échange entre le digestat et le tissu digestif. Le MeHg s'échange plus vite entre la solution et les sites, mais semble mettre un peu plus de temps à voyager jusqu'aux organes de bioaccumulation. En conclusion, l'étoile L. polaris, par sa taille, sa longévité et sa grande efficacité à digérer tout ce qui est ingéré, semble en mesure de jouer un rôle important à la fois dans la séquestration du MeHg et la remise en solution du Hg inorganique.In spite of a large body of work on the uptake of trace metals in aquatic organisms in the last two decades, very little attention has been devoted to echinoderms (urchins, starfish, and sea cucumbers, among the most important ones), a large group of invertebrates forming a major component of most coastal ecosystems. In the course of our research program on the role of echinoderms in the biogeochemical cycling of some trace metals in coastal environment, an experiment has been conducted on the uptake and the retention of mercury species with starfish Leptasterias polaris over a 40-day exposure period.Starfish were caught near Pointe-au-Père (Québec, Canada) and were acclimatized to laboratory conditions for 10 days in a flow-through aquarium. Forty stars (84 ± 14 g) were divided in two groups, kept in two aquariums, one for inorganic mercury and the other for methylmercury exposure. Animals were isolated from each other by mean of small 65-mm net cubicles allowing free circulation of seawater at a rate of 2 L.min-1. This flow rate provided a rapid renewal of seawater and ensured the elimination of any soluble mercury excreted during the course of the experiment. Control starfish receiving only uncontaminated mussels were also maintained in both aquariums to monitor the possible uptake of mercury from seawater. Blue mussels were collected in the vicinity of Pointe-au-Père and were contaminated following a technique described elsewhere (PELLETIER and LAROCQUE, 1987). Average levels of inorganic mercury and methylmercury (MeHg) in mussels were 13 ± 3 and 14 ± 4 mg.kg-1, respectively. Each starfish received one contaminated mussel per day over a 40-day period. Mussels were weighed before to be introduced in cages and their empty shells weighed again after ingestion by starfish in order to evaluate the amount of food and mercury taken up daily by each star. Two starfish were sampled in each aquarium every five days and dissected for pyloric caeca, gonads, and endoskeleton. Coelomic fluid was also collected. Both mercury species were analysed as total mercury (assuming a preservation level of ± 85-90% of the speciation during the course of the experiment) in biological tissues by cold vapour atomic adsorption spectrophotometry (detection limit=0.005 mg.kg-1 ww). The coefficient of variation was ± 15% and the recovery yield of MeHg-spiked samples was 92 ± 12%.The concentration of inorganic mercury reached 7.56 mg.kg-1 (wet weight) in pyloric caeca and the uptake rate was 0.22 mg.kg-1.d-1. Concentrations in gonads and endoskeleton were 10 to 20 times lower than in caeca (Fig. 1). The uptake rate of MeHg (0.17 mg.kg-1d-1) was slightly slower and the maximum concentration reached in caeca was 5.34 mg.kg-1. Mercury concentrations found in coelomic fluid were low and at least 100 times smaller than those in ceaca. No mercury was found in tissues of control starfish indicating that mercury excreted by diffusion in water by contaminated starfish was not re-adsorbed by other starfish in aquariums. The mercury load in each organ of stars was calculated and expressed as a percent (%) of total Hg uptake for each chemical species (Fig. 2). The inorganic Hg loads in pyloric caeca, gonads and endoskeleton reached a steady-state after only 10 days and remained unchanged up to the end of the experiment. The behaviour of MeHg was totally different as the loads in caeca decreased from 95% to 65% but increased from almost zero up to 30% in endoskeleton. Finally, the retention (%) of mercury species was calculated by dividing the actual total amount of mercury in each starfish by the total amount of mercury received from mussels (Fig. 3). The retention of inorganic Hg was about 50% throughout the exposure period whereas the retention of MeHg increased up to 90-95% at the end of the experiment.A kinetic model, based upon the assumption that the uptake process of Hg species in the digestive system is quite similar to an ion-exchange adsorption mechanism between a contamination solution and a solid surface, was developed. The integrated equation of the rate law was expressed as: (ln(C0-q))/q0-q = K'(C0m-q0)t + ln (C0m/q0)were Co is the initial concentration of mercury in the prey, qo is the maximun amount of mercury being absorbed, and m stands for the wet weight of the animal. This equation allowed the plot of its left-hand side against time and the slope provided an estimation of an apparent exchange rate constant for each mercury species (Fig. 4). The rate constant k'MeHg was slightly higher than k'Hg, indicating a faster exchange rate for MeHg between digested mussel tissues and binding sites (and also between sites) in caeca. However, a faster exchange rate do not mean a faster uptake rate because transport rate towards other organs also play an important role in the whole bioaccumulation process. In conclusion, starfish, by its ability to digest all ingested tissues, seems to be in a position to play a major role in the sequestration of methylmercury (high retention) from mussels and from other potential preys and in recycling inorganic mercury in solution (low retention). Starfish can be seen as "marine digester" which engulfs bivalves and other invertebrates (following species) and sends back soluble metabolites and trace metals which have not been bioaccumulated

Commentary: osteoarthritis of the knee and glucosamine

peer reviewe

Plasmonically Enhanced Reflectance of Heat Radiation from Low-Bandgap Semiconductor Microinclusions

Increased reflectance from the inclusion of highly scattering particles at low volume fractions in an insulating dielectric offers a promising way to reduce radiative thermal losses at high temperatures. Here, we investigate plasmonic resonance driven enhanced scattering from microinclusions of low-bandgap semiconductors (InP, Si, Ge, PbS, InAs and Te) in an insulating composite to tailor its infrared reflectance for minimizing thermal losses from radiative transfer. To this end, we compute the spectral properties of the microcomposites using Monte Carlo modeling and compare them with results from Fresnel equations. The role of particle size-dependent Mie scattering and absorption efficiencies, and, scattering anisotropy are studied to identify the optimal microinclusion size and material parameters for maximizing the reflectance of the thermal radiation. For composites with Si and Ge microinclusions we obtain reflectance efficiencies of 57 - 65% for the incident blackbody radiation from sources at temperatures in the range 400 - 1600 {\deg}C. Furthermore, we observe a broadbanding of the reflectance spectra from the plasmonic resonances due to charge carriers generated from defect states within the semiconductor bandgap. Our results thus open up the possibility of developing efficient high-temperature thermal insulators through use of the low-bandgap semiconductor microinclusions in insulating dielectrics.Comment: Main article (8 Figures and 2 Tables) + Supporting Information (8 Figures

Past dynamics of HIV transmission among men who have sex with men in Montréal, Canada: a mathematical modeling study

BACKGROUND: Gay, bisexual, and other men who have sex with men (gbMSM) experience disproportionate risks of HIV acquisition and transmission. In 2017, Montréal became the first Canadian Fast-Track City, setting the 2030 goal of zero new HIV infections. To inform local elimination efforts, we estimate the evolving role of prevention and sexual behaviours on HIV transmission dynamics among gbMSM in Montréal between 1975 and 2019. METHODS: Data from local bio-behavioural surveys were analyzed to develop, parameterize, and calibrate an agent-based model of sexual HIV transmission. Partnership dynamics, HIV's natural history, and treatment and prevention strategies were considered. The model simulations were analyzed to estimate the fraction of HIV acquisitions and transmissions attributable to specific groups, with a focus on age, sexual partnering level, and gaps in the HIV care-continuum. RESULTS: The model-estimated HIV incidence peaked in 1985 (2.3 per 100 person years (PY); 90% CrI: 1.4-2.9 per 100 PY) and decreased to 0.1 per 100 PY (90% CrI: 0.04-0.3 per 100 PY) in 2019. Between 2000-2017, the majority of HIV acquisitions and transmissions occurred among men aged 25-44 years, and men aged 35-44 thereafter. The unmet prevention needs of men with > 10 annual anal sex partners contributed 90-93% of transmissions and 67-73% of acquisitions annually. The primary stage of HIV played an increasing role over time, contributing to 11-22% of annual transmissions over 2000-2019. In 2019, approximately 70% of transmission events occurred from men who had discontinued, or never initiated antiretroviral therapy. CONCLUSIONS: The evolving HIV landscape has contributed to the declining HIV incidence among gbMSM in Montréal. The shifting dynamics identified in this study highlight the need for continued population-level surveillance to identify gaps in the HIV care continuum and core groups on which to prioritize elimination efforts

Immunogenicity, safety, and efficacy of the HPV vaccines among people living with HIV: A systematic review and meta-analysis

Background: Vaccines have been demonstrated to protect against high-risk human papillomavirus infection (HPV), including HPV-16/18, and cervical lesions among HIV negative women. However, their efficacy remains uncertain for people living with HIV (PLHIV).We systematically reviewed available evidence on HPV vaccine on immunological, virological, or other biological outcomes in PLHIV. Methods: We searched five electronic databases (PubMed, Medline and Embase, clinicaltrials.gov and the WHO clinical trial database) for longitudinal prospective studies reporting immunogenicity, virological, cytological, histological, clinical or safety endpoints following prophylactic HPV vaccination among PLHIV. We included studies published by February 11th, 2021. We summarized results, assessed study quality, and conducted meta-analysis and subgroup analyses, where possible. Findings: We identified 43 publications stemming from 18 independent studies (Ns =18), evaluating the quadrivalent (Ns =15), bivalent (Ns =4) and nonavalent (Ns =1) vaccines. A high proportion seroconverted for the HPV vaccine types. Pooled proportion seropositive by 28 weeks following 3 doses with the bivalent, quadrivalent, and nonavalent vaccines were 0.99 (95% confidence interval: 0.95-1.00, Ns =1), 0.99 (0.98-1.00, Ns =9), and 1.00 (0.99-1.00, Ns =1) for HPV-16 and 0.99 (0.96-1.00, Ns =1), 0.94 (0.91-0.96, Ns =9), and 1.00 (0.99-1.00, Ns =1) for HPV-18, respectively. Seropositivity remained high among people who received 3 doses despite some declines in antibody titers and lower seropositivity over time, especially for HPV-18, for the quadrivalent than the bivalent vaccine, and for HIV positive than negative individuals. Seropositivity for HPV-18 at 29-99 weeks among PLHIV was 0.72 (0.66-0.79, Ns =8) and 0.96 (0.92-0.99, Ns =2) after 3 doses of the quadrivalent and bivalent vaccine, respectively and 0.94 (0.90-0.98, Ns =3) among HIV-negative historical controls. Evidence suggests that the seropositivity after vaccination declines over time but it can lasts at least 2-4 years. The vaccines were deemed safe among PLHIV with few serious adverse events. Evidence of HPV vaccine efficacy against acquisition of HPV infection and/or associated disease from the eight trials available was inconclusive due to the low quality. Interpretation: PLHIV have a robust and safe immune response to HPV vaccination. Antibody titers and seropositivity rates decline over time but remain high. The lack of a formal correlate of protection and efficacy results preclude definitive conclusions on the clinical benefits. Nevertheless, given the burden of HPV disease in PLHIV, although the protection may be shorter or less robust against HPV-18, the robust immune response suggests that PLHIV may benefit from receiving HPV vaccination after acquiring HIV. Better quality studies are needed to demonstrate the clinical efficacy among PLHIV. Funding: World Health Organization. MRC Centre for Global Infectious Disease Analysis, Canadian Institutes of Health Research, UK Medical Research Council (MRC)

Automatic radiographic quantification of hand osteoarthritis; accuracy and sensitivity to change in joint space width in a phantom and cadaver study

This is the final version of the article. Available from Springer Verlag via the DOI in this record.OBJECTIVE: To validate a newly developed quantification method that automatically detects and quantifies the joint space width (JSW) in hand radiographs. Repeatability, accuracy and sensitivity to changes in JSW were determined. The influence of joint location and joint shape on the measurements was tested. METHODS: A mechanical micrometer set-up was developed to define and adjust the true JSW in an acrylic phantom joint and in human cadaver-derived phalangeal joints. Radiographic measurements of the JSW were compared to the true JSW. Repeatability, systematic error (accuracy) and sensitivity (defined as the smallest detectable difference (SDD)) were determined. The influence of joint position on the JSW measurement was assessed by varying the location of the acrylic phantom on the X-ray detector with respect to the X-ray beam and the influence of joint shape was determined by using morphologically different human cadaver joints. RESULTS: The mean systematic error was 0.052 mm in the phantom joint and 0.210 mm in the cadaver experiment. In the phantom experiments, the repeatability was high (SDD = 0.028 mm), but differed slightly between joint locations (p = 0.046), and a change in JSW of 0.037 mm could be detected. Dependent of the joint shape in the cadaver hand, a change in JSW between 0.018 and 0.047 mm could be detected. CONCLUSIONS: The automatic quantification method is sensitive to small changes in JSW. Considering the published data of JSW decline in the normal and osteoarthritic population, the first signs of OA progression with this method can be detected within 1 or 2 years.This work was funded by the Dutch Arthritis Association (Reumafonds). The study sponsor had no involvement in study design, data collection, data analysis, or interpretation of the results

Impact of Community-Based Larviciding on the Prevalence of Malaria Infection in Dar es Salaam, Tanzania.

The use of larval source management is not prioritized by contemporary malaria control programs in sub-Saharan Africa despite historical success. Larviciding, in particular, could be effective in urban areas where transmission is focal and accessibility to Anopheles breeding habitats is generally easier than in rural settings. The objective of this study is to assess the effectiveness of a community-based microbial larviciding intervention to reduce the prevalence of malaria infection in Dar es Salaam, United Republic of Tanzania. Larviciding was implemented in 3 out of 15 targeted wards of Dar es Salaam in 2006 after two years of baseline data collection. This intervention was subsequently scaled up to 9 wards a year later, and to all 15 targeted wards in 2008. Continuous randomized cluster sampling of malaria prevalence and socio-demographic characteristics was carried out during 6 survey rounds (2004-2008), which included both cross-sectional and longitudinal data (N = 64,537). Bayesian random effects logistic regression models were used to quantify the effect of the intervention on malaria prevalence at the individual level. Effect size estimates suggest a significant protective effect of the larviciding intervention. After adjustment for confounders, the odds of individuals living in areas treated with larviciding being infected with malaria were 21% lower (Odds Ratio = 0.79; 95% Credible Intervals: 0.66-0.93) than those who lived in areas not treated. The larviciding intervention was most effective during dry seasons and had synergistic effects with other protective measures such as use of insecticide-treated bed nets and house proofing (i.e., complete ceiling or window screens). A large-scale community-based larviciding intervention significantly reduced the prevalence of malaria infection in urban Dar es Salaam

Can HIV self-testing reach first-time testers? A telephone survey among self-test end users in Côte d'Ivoire, Mali, and Senegal

BACKGROUND: Coverage of HIV testing remains sub-optimal in West Africa. Between 2019 and 2022, the ATLAS program distributed ~400 000 oral HIV self-tests (HIVST) in Côte d'Ivoire, Mali, and Senegal, prioritising female sex workers (FSW) and men having sex with men (MSM), and relying on secondary redistribution of HIVST to partners, peers and clients to reach individuals not tested through conventional testing. This study assesses the proportion of first-time testers among HIVST users and the associated factors. METHODS: A phone-based survey was implemented among HIVST users recruited using dedicated leaflets inviting them to anonymously call a free phone number. We collected socio-demographics, sexual behaviours, HIV testing history, HIVST use, and satisfaction with HIVST. We reported the proportion of first-time testers and computed associated factors using logistic regression. RESULTS: Between March and June 2021, 2 615 participants were recruited for 50 940 distributed HIVST (participation rate: 5.1%). Among participants, 30% received their HIVST kit through secondary distribution (from a friend, sexual partner, family member, or colleague). The proportion who had never tested for HIV before HIVST (first-time testers) was 41%. The main factors associated with being a first-time tester were sex, age group, education level, condom use, and secondary distribution. A higher proportion was observed among those aged 24 years or less (55% vs 32% for 25-34, aOR: 0.37 [95%CI: 0.30-0.44], and 26% for 35 years or more, aOR: 0.28 [0.21-0.37]); those less educated (48% for none/primary education vs 45% for secondary education, aOR: 0.60 [0.47-0.77], and 29% for higher education, aOR: 0.33 [0.25-0.44]). A lower proportion was observed among women (37% vs 43%, aOR: 0.49 [0.40-0.60]); those reporting always using a condom over the last year (36% vs 51% for those reporting never using them, aOR: 2.02 [1.59-2.56]); and those who received their HISVST kit through primary distribution (39% vs 46% for secondary distribution, aOR: 1.32 [1.08-1.60]). CONCLUSION: ATLAS HIVST strategy, including secondary distribution, successfully reached a significant proportion of first-time testers. HIVST has the potential to reach underserved populations and contribute to the expansion of HIV testing services in West Africa