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Changing patterns of malaria in Grande Comore after a drastic decline : importance of fine-scale spatial analysis to inform future control actions
No full textMalaria has long been endemic in the Union of Comoros reaching an incidence of 15,045 cases for 100,000 inhabitants in 2010 (103,670 cases). Since then, strengthened control actions based on the distribution of Long-Lasting Insecticidal mosquito Nets and mass treatment have reduced malaria to a low level. However, it persists more specifically in Grande Comore, where 82% of cases were diagnosed between 2010 and 2016. This situation remains a challenge for health authorities seeking to eliminate malaria, by targeting transmission sites more precisely. In this context, this study aimed at mapping malaria at the finest scale, in order to describe its spatial distribution and identify possible environmental indicators. The National Malaria Control Program provided the 2016 data, the only year that could be mapped at the level of localities. This mapping revealed spatial autocorrelation between localities, especially in the east of the island with a major cluster around Itsinkoudi (using the Kulldorff's spatial scan test). Secondary clusters showed that malaria remains present throughout the island in both rural and urban areas. We also analyzed satellite images (SPOT 5) with remote sensing techniques (Object-Based Image Analysis) to look for environmental indicators. Landscape analysis shows that malaria incidence is correlated across the island with low altitudes, and a larger proportion of grasslands or a fewer proportion of forested areas nearby (at less than 1km around villages). More locally in the east, malaria is linked to larger shrub areas. These relationships could be associated with the fact that lower altitude localities are more interconnected, such facilitating malaria transmission. In 2016, malaria persists in Grande Comore, showing new patterns with more cases in the eastern part of the island and the possibility of high incidences during the dry season. Precise mapping of epidemiological data and landscape analysis allow the identification of clusters and active transmission foci. They are important tools for health surveillance in order to optimize control actions on key transmission locations
Bisphenol A removal by the Chlorophyta Picocystis sp. : optimization and kinetic study
No full textThe Chlorophyta Picocystis sp. isolated from a Tunisian household sewage pond appears promising for effective removal of Bisphenol A (BPA). Efficient and cost-effective technology for contaminants remediation relies on a tradeoff between several parameters such as removal efficiency, microorganism growth, and its tolerance to contaminant toxicity. This article demonstrates the optimum conditions achieving the highest removal rates and the minimal growth inhibition in batch cultures of Picocystis using response surface methodology. A central composite face-centered (CCF) design was used to determine the effects on removal and growth inhibition of four operating parameters: temperature, inoculum cell density, light intensity, and initial BPA concentration. Results showed that the maximal BPA removal was 91.36%, reached the optimal culture conditions of 30.7 degrees C, 25 x 10(5) cells ml(-1) inoculum density, 80.6 mu mol photons m(-2) s(-1) light intensity, and initial BPA concentration of 10 mg l(-1). Various substrate inhibition models were used to fit the experimental data, and robustness analysis highlighted the Tessier model as more efficient to account for the interaction between Picocystis and BPA and predict removal efficiency. These results revealed how Picocystis respond to BPA contamination and suggest that optimization of experimental conditions can be effectively used to maximize BPA removal in the treatment process
Plasmodium falciparum sexual parasites regulate infected erythrocyte permeability
No full textBouyer et al. report that the new permeation pathways (NPP), responsible of modulating erythrocyte permeability to diverse solutes and considered only to be in pathogenic asexual stages of P. falciparum, are also active in erythrocytes infected with immature gametocytes and this activity declines with gametocyte maturation. NPPs are regulated by the cAMP signalling cascade, and the decrease in cAMP levels in mature stages slows NPP activity. To ensure the transport of nutrients necessary for their survival, Plasmodium falciparum parasites increase erythrocyte permeability to diverse solutes. These new permeation pathways (NPPs) have been extensively characterized in the pathogenic asexual parasite stages, however the existence of NPPs has never been investigated in gametocytes, the sexual stages responsible for transmission to mosquitoes. Here, we show that NPPs are still active in erythrocytes infected with immature gametocytes and that this activity declines along gametocyte maturation. Our results indicate that NPPs are regulated by cyclic AMP (cAMP) signaling cascade, and that the decrease in cAMP levels in mature stages results in a slowdown of NPP activity. We also show that NPPs facilitate the uptake of artemisinin derivatives and that phosphodiesterase (PDE) inhibitors can reactivate NPPs and increase drug uptake in mature gametocytes. These processes are predicted to play a key role in P. falciparum gametocyte biology and susceptibility to antimalarials
Fault-zone damage promotes pulse-like rupture and back-propagating fronts via quasi-static effects
No full textDamage zones are ubiquitous components of faults that may affect earthquake rupture. Simulations show that pulse-like rupture can be induced by the dynamic effect of waves reflected by sharp fault zone boundaries. Here we show that pulses can appear in a highly damaged fault zone even in the absence of reflected waves. We use quasi-static scaling arguments and quasi-dynamic earthquake cycle simulations to show that a crack turns into a pulse after the rupture has grown larger than the fault zone thickness. Accompanying the pulses, we find complex rupture patterns involving back-propagating fronts that emerge from the primary rupture front. Our model provides a mechanism for back-propagating fronts recently observed during large earthquakes. Moreover, we find that slow-slip simulations in a highly compliant fault zone also produce back-propagating fronts, suggesting a new mechanism for the rapid tremor reversals observed in Cascadia and Japan. Plain Language Summary Damage zones are zones of fractured rock that surround faults and can influence how earthquakes propagate. Previous computer models show that damage zones promote an inchworm-like (rather than zipper-like) pattern of earthquake propagation, known as pulses. This finding has been previously attributed to the effect of seismic waves reflected at the boundaries of the damage zone. Here, we show that pulses are generated in highly fractured damage zones independently of the reflection of seismic waves. We reach this conclusion by scaling arguments confirmed by numerical simulations of sequences of earthquakes in which we ignore the reflection of seismic waves. Moreover, our models produce an unexpected pattern of earthquake propagation: Secondary rupture fronts emerge from the primary rupture front and propagate in the opposite direction. Similar back-propagating fronts have been previously observed during slow earthquakes in subduction zones and more recently during large earthquakes. Our work reveals a possible connection between an observable structural feature of faults and complicated patterns of earthquake propagation. Key Points Highly damaged fault zones promote pulse-like ruptures even without the dynamic effects of reflected waves Slip complexity induced by fault damage involves multiple back-propagating rupture fronts A new mechanism for rapid tremor reversals is observed during episodic tremor and sli
Projected effects of climate-induced changes in hydrodynamics on the biogeochemistry of the Mediterranean Sea under the RCP 8.5 regional climate scenario
No full textThe Mediterranean region has been shown to be particularly exposed to climate change, with observed trends that are more pronounced than the global tendency. In forecast studies based on a RCP 8.5 scenario, there seems to be a consensus that, along with an increase in temperature and salinity over the next century, a reduction in the intensity of deep-water formation and a shallowing of the mixed layer [especially in the North-Western Mediterranean Sea (MS)] are expected. By contrast, only a few studies have investigated the effects of climate change on the biogeochemistry of the MS using a 3D physical/biogeochemical model. In this study, our aim was to explore the impact of the variations in hydrodynamic forcing induced by climate change on the biogeochemistry of the MS over the next century. For this purpose, high-resolution simulations under the RCP 8.5 emission scenario have been run using the regional climate system model CNRM-RCSM4 including the NEMO-MED8 marine component, coupled (off-line) with the biogeochemical model Eco3M-Med. The results of this scenario first highlight that most of the changes in the biogeochemistry of the MS will occur (under the RCP 8.5 scenario) after 2050. They suggest that the MS will become increasingly oligotrophic, and therefore less and less productive (14% decrease in integrated primary production in the Western Basin and in the Eastern Basin). Significant changes would also occur in the planktonic food web, with a reduction (22% in the Western Basin and 38% in the Eastern Basin) of large phytoplankton species abundance in favor of small organisms. Organisms will also be more and more N-limited in the future since NO3 concentrations are expected to decline more than those of PO4 in the surface layer. All these changes would mainly concern the Western Basin, while the Eastern Basin would be less impacted
Pantropical variability in tree crown allometry
No full textAim Tree crowns determine light interception, carbon and water exchange. Thus, understanding the factors causing tree crown allometry to vary at the tree and stand level matters greatly for the development of future vegetation modelling and for the calibration of remote sensing products. Nevertheless, we know little about large-scale variation and determinants in tropical tree crown allometry. In this study, we explored the continental variation in scaling exponents of site-specific crown allometry and assessed their relationships with environmental and stand-level variables in the tropics. Location Global tropics. Time period Early 21st century. Major taxa studied Woody plants. Methods Using a dataset of 87,737 trees distributed among 245 forest and savanna sites across the tropics, we fitted site-specific allometric relationships between crown dimensions (crown depth, diameter and volume) and stem diameter using power-law models. Stand-level and environmental drivers of crown allometric relationships were assessed at pantropical and continental scales. Results The scaling exponents of allometric relationships between stem diameter and crown dimensions were higher in savannas than in forests. We identified that continental crown models were better than pantropical crown models and that continental differences in crown allometric relationships were driven by both stand-level (wood density) and environmental (precipitation, cation exchange capacity and soil texture) variables for both tropical biomes. For a given diameter, forest trees from Asia and savanna trees from Australia had smaller crown dimensions than trees in Africa and America, with crown volumes for some Asian forest trees being smaller than those of trees in African forests. Main conclusions Our results provide new insight into geographical variability, with large continental differences in tropical tree crown allometry that were driven by stand-level and environmental variables. They have implications for the assessment of ecosystem function and for the monitoring of woody biomass by remote sensing techniques in the global tropics
La lutte antivectorielle : comprendre où en est la recherche
No full textL'expansion rapide et l'implantation durable du moustique tigre (Aedes albopictus) en France métropolitaine et dans les territoires d'outre-mer font craindre le déclenchement de foyers épidémiques d'arboviroses telles la dengue, le chikungunya et la fièvre Zika. En l'absence de traitements ou de vaccins efficaces, la lutte anti-vectorielle (LAV) est la seule méthode envisageable pour contrôler ce risque et diminuer les densités de moustiques du genre Aede
Iron incorporation from seawater into Antarctic sea ice : a model study
No full textSea ice acts as an iron (Fe) reservoir in the Southern Ocean (SO) where primary productivity is largely Fe limited. The mechanisms leading to Fe enrichment in sea ice result from the combination of poorly understood and largely unexplored physical and biological processes. We analyze the biogeochemical impacts of three plausible idealized formulations of dissolved Fe (DFe) incorporation into sea ice corresponding to (i) constant Fe concentration in sea ice, (ii) constant ocean-ice Fe flux, and (iii) ocean-ice Fe flux linearly varying with seawater Fe concentration in a global ocean-sea-ice-biogeochemical model, focusing on the SO. The three formulations simulate different geographical distributions of DFe concentrations in sea ice. Iron in sea ice remains largely uncertain due to the limited number of spatial and seasonal observations, poorly constrained Fe sources and sinks, and significant uncertainties in simulated sea ice and hydrography. Despite these differences, the fertilization effect by sea ice on phytoplankton photosynthesis is qualitatively similar regardless of the formulation considered. Iron incorporation during sea-ice formation, transport, and melt release, common to all formulations, dominates over differences in sea-ice Fe concentrations. Formulating the Fe incorporation rate as proportional to seawater Fe concentrations gives the closest agreement to field observations. With this formulation, sediments work in synergy with Fe transport to fertilize the waters north of the continental shelf. Southern Ocean primary production and export production increase by 5-10% and 9-19%, respectively, when Fe incorporation into sea ice is considered, suggesting a moderate effect of Fe-bearing sea ice on marine productivity
Magnetic properties of ferritchromite and Cr-magnetite and monitoring of Cr-spinels alteration in ultramafic and mafic rocks
No full textSpinel is a ubiquitous mineral in mafic/ultramafic rocks. Spinel cores chemistry is extensively used as a petrogenetic proxy while their alteration phases, ferritchromite, and Cr-magnetite, are used as metamorphic grade indicators. However, the magnetic properties and composition of these phases are still ill-defined and no consensus exists concerning the metamorphic conditions involved in their formation. Here, we use the magnetic properties of these Cr-spinel alteration phases, via field-dependent parameters and observations with a magnetic microscope coupled with mineral chemistry and Mossbauer spectroscopy, to better constrain their composition. We identify Cr-magnetite by a Curie point of ca. 520 degrees C. We show that it is characterized by an n between 0.1 and 0.2 in the Fe-Cr spinel formula [Fe2+(Fe1-nCrn)(2)O-4], which corresponds to 6-13 wt.% of Cr2O3. The abundance of Cr-magnetite indicates a strong alteration of Cr-spinels that could reflect a significant hydrothermal activity rather than a high metamorphism grade. Normalized variation curves of the magnetic susceptibility during heating allow a relative quantification of the contributions of different magnetic phases to the magnetic susceptibility. This highlights a link between ferritchromite destabilization into maghemite at ca. 130 degrees C followed by the destabilization of this maghemite starting at 300 degrees C. We identify specific covariation trends between these two magnetic species characterizing different alteration processes. This study opens the door to magnetic monitoring of the Cr-spinel alteration state in mafic and ultramafic rocks. It constitutes a new, fast, and weakly destructive way to study the petrological history of both terrestrial and extraterrestrial rocks