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International audience; The incorporation of the spatial heterogeneity of real landscapes into population dynamics remains extremely difficult. We propose combining equation-based modelling (EBM) and agent-based modelling (ABM) to overcome the difficulties classically encountered. ABM facilitates the description of entities that act according to specific rules evolving on various scales. However, a large number of entities may lead to computational difficulties (e.g., for populations of small mammals, such as voles, that can exceed millions of individuals). Here, EBM handles age-structured population growth, and ABM represents the spreading of voles on large scales. Simulations applied to the spreading of a montane water vole population demonstrated that our model is quite efficient in representing the pattern observed and might help to highlight some key parameters during population expansion. This method paves the way for further developments, including the introduction of density-dependent parameters (predation, diseases, etc.) capable of triggering population declines in an explicitly spatial context.

International audience; Malarial infections have long been recognized as a driver of human evolution, as demonstrated by the influence of Plasmodium falciparum on sickle-cell anemia persistence. Duffy-negativity is another blood disorder thought to have been selected because it confers nearly complete resistance against Plasmodium vivax infection. Recent evidence suggests that the benefits of being Duffy-negative cannot be expected to play a strong selective pressure on humans, whereas its costs cannot be considered as negligible. Here, we suggest that the cross-talk between P. falciparum and P. vivax in coinfected children could represent the most parsimonious explanation of the frequency of Duffy-negativity. We discuss how this new hypothesis could be tested and call for a reconsideration of the evolution of the Duffy-negative group.

This paper presents a geometrical model of soil pore space based on the quantitative analysis of synchrotron X-ray microtomography data. Our model calculated the minimal set of balls that recovered the skeleton of the pore space using Delaunay tessellation, and the simply connected sets of balls that could be considered as potential pore channels. This model (DTM software) was then applied to three-dimensional tomography reconstructions of soil aggregates (~ 5 mm diameter) from two management systems (conventionally tilled soil, namely CTT and grassland soil, namely GL) with a voxel edge length of 3.2 μm and 5.4 μm, respectively. Geometric characteristics such as the frequency distribution of pore radius, length, and tortuosity as well as the retention curve were calculated using our model. The organic matter decomposition was also simulated using DTM approach. The results were compared with pore space statistics obtained during a previously published study on the same data using algorithms based on the medial axis and throat computation ( 3dma software). The same tendency on the geometrical statistic was obtained using both methods, with more pores of smaller length and diameter calculated for the aggregate from the conventionally tilled site compared to the grassland aggregate. However, the 3dma method generated a larger quantity of voxels (385,673 and 189,250 for CTT and GL, respectively) compared to the amount of balls in DTM (170,250 and 64,273 for CTT and GL, respectively) and shorter channels because of the presence of throats.

Background Sexual transmission of Ebola virus disease (EVD) 6 months after onset of symptoms has been recently documented, and Ebola virus RNA has been detected in semen of survivors up to 9 months after onset of symptoms. As countries affected by the 2013–2015 epidemic in West Africa, by far the largest to date, are declared free of Ebola virus disease (EVD), it remains unclear what threat is posed by rare sexual transmission events that could arise from survivors. Methodology/Principal Findings We devised a compartmental mathematical model that includes sexual transmission from convalescent survivors: a SEICR (susceptible-exposed-infectious-convalescent-recovered) transmission model. We fitted the model to weekly incidence of EVD cases from the 2014–2015 epidemic in Sierra Leone. Sensitivity analyses and Monte Carlo simulations showed that a 0.1% per sex act transmission probability and a 3-month convalescent period (the two key unknown parameters of sexual transmission) create very few additional cases, but would extend the epidemic by 83 days [95% CI: 68–98 days] (p < 0.0001) on average. Strikingly, a 6-month convalescent period extended the average epidemic by 540 days (95% CI: 508–572 days), doubling the current length, despite an insignificant rise in the number of new cases generated. Conclusions/Significance Our results show that reductions in the per sex act transmission probability via abstinence and condom use should reduce the number of sporadic sexual transmission events, but will not significantly reduce the epidemic size and may only minimally shorten the length of time the public health community must maintain response preparedness. While the number of infectious survivors is expected to greatly decline over the coming months, our results show that transmission events may still be expected for quite some time as each event results in a new potential cluster of non-sexual transmission. Precise measurement of the convalescent period is thus important for planning ongoing surveillance efforts., Author Summary Researchers have recently raised suspicion that the Ebola virus can be transmitted sexually from survivors after recovering from the life-threatening acute phase characteristic of Ebola virus disease (EVD). However, the nature of the impact sexual transmission from convalescent survivors may have on disease dynamics remains unknown. Mathematical models are useful for translating empirical uncertainty into a range of possible outcomes. We formalized an epidemiological model that accounts for a secondary route of transmission of EVD through sexual contact with otherwise healthy survivors. We found that while very few additional cases are expected, a 3-month period of convalescent infectivity could extend the 2014–2015 Sierra Leone epidemic by nearly 3 months, and a 6-month convalescent period could double the current length by extending it an additional 18 months. Our results reveal that measures to reduce sexual contact between survivors and susceptible individuals are not likely to have a major impact on the length of time affected public health communities must remain vigilant, and highlight the need for ongoing surveillance efforts.