Effet du confiage d'animaux dans la propagation d'une maladie contagieuse au sein d'un réseau structuré de troupeaux : exemple de la péripneumonie contagieuse bovine dans les troupeaux éthiopiens

La péripneumonie contagieuse bovine est une maladie respiratoire des bovins, d'importance économique majeure. Son actuelle ré-émergence en fait l'une des principales menaces pour la production et la santé animale en Afrique Subsaharienne. La modélisation de la PPCB s'appuie sur la structure de la population bovine : les niveaux intra-troupeau et inter-troupeaux. Le modèle intra-troupeau se base sur un modèle compartimenta! SEI3R. La modélisation à deux échelles des coefficients de transmission pour chaque stade infectant (une globale liée aux contacts aériens et une locale liée au contact direct) permet la détermination de leurs valeurs en conditions expérimentales. L'étude de l'influence des distributions des temps de séjour montre la meilleure aptitude des distributions de type gaussien à reproduire la dynamique de propagation intra-troupeau par rapport aux distributions exponentielles classiquement employées, alors que les deux modèles donnent des résultats semblables en terme de mortalité et d'incidences clinique et chronique. Le modèle inter-troupeau est basé sur la construction d'un réseau de troupeaux à l'intérieur desquels la dynamique de la maladie est celle du modèle intra-troupeau. Les dynamiques obtenues, avec des taux de confiage réalistes, sont différentes de celles d'un modèle sous hypothèse de mélange homogène. La propagation spatiale de la maladie, et sa sensibilité aux différents paramètres du modèle sont étudiées. Finalement, il est montré comment le modèle peut être utilisé pour tester l'effet de différentes stratégies de lutte sur la propagation de la PPCB dans un réseau de troupeaux. (Résumé d'auteur

Exploring Culicoides species communities at continental scale: a unique collaborative approach

Culicoides biting midges were responsible for continental scale epizootics of viruses, including several bluetongue virus (BTV) serotypes. The existence of epi-zones has been suggested to explain the geographical range of the spread of BTV serotypes. The structure of Culicoides populations may contribute to the definition of these epi-zones, whereas their movements may be involved in their connections. One of the objectives of the PALE-Blu project (Understanding pathogen, livestock, environment interactions involving bluetongue virus) is to determine if the composition of Culicoides species communities may be involved in the existence of these epi-zones. For this purpose, an extensive dataset of abundance data, focusing on the most common Culicoides species, was established. We used as long as possible longitudinal Culicoides follow-ups carried out with UV light-traps. The yearly maximum abundance (i.e. the largest single night trap catch in the collecting period) was used to aggregate data against time and to pro-duce an index of the species abundance. If the collection period covers several years, then we used the average of the yearly maxima of abundance for Culicoides obsoletus/Culicoides scoticus, Culicoides imicola, Culicoides chiopterus, Culicoides dewulfi, Culicoides puli-caris/Culicoides lupicaris, Culicoides punctatus, Culicoides newsteadi, and Culicoides kingi. The gathered data may have been shared by National surveillance systems or have been produced by VectorNet (2014-2018), which is a joint initiative of the European Food Safety Authority (EFSA) and the European Centre for Disease Prevention and Control (ECDC). This project supported the collection of data on vectors, related to both animal and human health, to map the presence/absence of vectors in Europe (in the geograph-ical sense) and around the Mediterranean basin. The VectorNet data were obtained by a formal request to ECDC (reference number 18-1421). The final dataset contains a total of 639 sites from 27 countries (from Senegal to Scandinavia, and from Iceland to Tur-key). The existence of this database was only possible by a collaborative approach, in-volving 29 partners. The purpose of this poster was to thank contributors and enhanced future collaborations at continental scale

World Health Organisation test applied on Culicoides: a multicentric study

The aim of this work is to organize a multicentric assay to compare susceptibilities of Culicoides populations to insecticides (i.e. C. imicola and C. obsoletus sensu stricto). The base line of the World Health Organisation test kit (WHO/VBC81.805) is to expose mosquitoes to papers impregnated with insecticides to detect the resistance of Anopheles (paludism vector) in the field. In a novel approach, the WHO test can be used on Culicoides to assess midges' susceptibility to insecticides. Information on the intrinsic susceptibilities to insecticides is required to assess correctly the existing (or new) formulations of insecticide. This multicentric assay will improve our capacity to experiment by networking and assess the population variability by comparing susceptibilities between different populations of Culicoides. Field-collected midges are trapped alive using an ultraviolet light trap (OVI model, South Africa) and replacing the collection jar with a fine mesh cage. To prevent desiccation, cages are covered with wet papers, wrapped in aluminium foil and retrieved at dawn. It is important to choose the site and period with abundant target species to improve robustness with more individuals. Experiments should be carried out in an insecticide-free environment with constant temperature and humidity, and started a few hours after collection. Insecticide-impregnated papers are rolled and fastened into the WHO kit test tube. About 30 Culicoides (approximately 20 nulliparous females) are collected and transferred to the tube. Tubes are maintained horizontally for an hour (exposure to insecticide). Mortalities are recorded 1 h and 24 h after exposure. One control is performed without insecticide to validate the test. Mortalities are analysed by probit regression to obtain LC50 and LC90 for each population. The test has to be run at least with four concentrations of insecticide, one control and four replicates with samples from the same population. Only nulliparous females are recorded. Insecticide concentrations are given in percentages (WHO standard). In this WHO test, the target species are C. imicola and C. obsoletus s.s., and the active ingredient used is deltamethrin at doses 0.005, 0.001, 0.0005 and 0.0001%. Data will be centralized and analysed by EID-Méditerranée (France), and results will be given back to the partners and published. Future studies could focus on comparing the four deltamethrin concentrations on other species and testing Culicoides susceptibility to other components. (Texte intégral

Theoretical formulation for mosquito host-feeding patterns : Application to a west nile virus focus of Southern France

Host-feeding patterns play a key role in the transmission of vector-borne diseases such as West Nile fever, which involves two kinds of vertebrates, birds and mammals. In this study, we propose a theoretical formulation for mosquito host-feeding patterns using three quantities, as follows: the apparent attractiveness/contact probabilities, the conditional host(-feeding) preferences, and the enzootic versus bridge probabilities. Using results from host-baited trap collections, the quantities deÞned above were assessed for the most abundant mosquito species in the main West Nile virus focus of southern France.Wefound that host availability is important in determining the efÞciency of bridge vectors, and that even ornithophilic mosquitoes like Culex species, classically classiÞed as enzootic vectors, may turn out to be efÞcient bridge vectors in certain contexts of host abundance. Our developed theoretical framework can easily be adapted and applied to other experimental data and other vector-borne diseases. (Résumé d'auteur

Vector competence of British Culicoides species for Bluetongue virus serotype 8

The proportion of infected vectors which are able to transmit an arbovirus to a susceptible host has a significant impact on the epidemic potential of such a virus. Assessing vector competence is therefore crucial to evaluate accurately the risk posed by such a disease to any non-endemic region. The vector competence of various Culicoides species in Scotland for bluetongue virus serotype 8 (BTV-8) was assessed by a pad-feeding technique, and a high-throughput virus extraction and isolation procedure. This was coupled with a multiplex polymerase chain reaction (PCR) to identify members of the Culicoides Obsoletus complex to species level. These results are compared with vector competence results of further Culicoides Obsoletus in South-East England assessed by the same method. A very low level of competence for this strain was detected in all Culicoides species tested, similar to that described for this strain in C. imicola originating from both Corsica and the Onderstepoort Veterinary Institute in South Africa. The implications of this are discussed in relation to future studies and also with regard to wider aspects of orbivirus transmission in the European Union. (Texte intégral

Use of entomology surveillance data for Culicoides abundance modeling in mainland France

In France, Culicoides surveillance was implemented in 2002 [1] in specific areas (Corsica and Mediterranean coastal mainland) and in the whole metropolitan France from 2009 to monitor vectors activity during the bluetongue epizootics. The Directorate for food of the French Agriculture ministry (DGAL) mandated the French Agricultural Research Centre for International Development (CIRAD) to achieve this entomological surveillance. The national-scale surveillance program ceased in 2012 and was implemented again following the re-emergence of bluetongue in 2015 [2]. Since November 2016, surveillance in mainland France is implemented in 24 eco-climatic zones which are homogenous in terms of vector phenology (start and end of activity period), abundance and diversity [3, 4]. The purpose of this study was to measure the effect of several factors influencing the abundance of Culicoides for every eco-climatic zone. We applied a specific count model to measure the impact of several factors associated to the Culicoides abundance for every eco-climatic zone from the second week of 2009 to the last week of 2012. As explanatory variables we use the week number, the catch site and the year of trapping. The environmental component was considered through the eco-climatic zoning of mainland [3, 4]. Overall, the results fit the data for the 24 eco-climatic zones. They showed that the abundance of Culicoides in mainland France clearly depend on the areas with different shape of dynamics (one or two peaks, with or without plateaus). Even if our data were not collected with this goal, our study shows Culicoides abundance can be predicted in each zones for a standard year. Our models are going to be used to model bluetongue virus serotype 8 (BTV8) spreading in mainland France. Indeed, efficiency evaluation of French surveillance and control system against BTV8 through informatic simulations requires disease diffusion model

The Culicoides of the subgenus Avaritia (Diptera: Ceratopogonidae) in the Palaearctic region: through unsuspected diversity with epidemiologic implications

The biting midges of the genus Culicoides (Diptera: Ceratopogonidae) are known vectors of pathogens especially Orbivirus of the Reoviridae family such as bluetongue, african horse sickness, epizootic hemorrhagic disease and more recently Schmallenberg viruses. The western Europe and the Mediterranean basin faced bluetongue transmission with the 6 species belonging to the Avaritia subgenus recorded in these areas including the species closely related to the Obsoletus group. To date, no study encompasses the whole number of species belonging to a subgenus at a biogeographical scale. The data presented focus on local or on country fauna scale using a classification based on subgenus and/or group of species. Among the latter, the presence of cryptic species has been pointed out by recent phylogenetic studies. These classification discrepancies between authors since decades result in a taxonomic imbroglio. Recent findings of specimens with tricky morphology related to the Obsoletus group in France led us to better describe the systematic and the taxonomy of the subgenus Avaritia in the Palaearctic region. This study focuses on investigating the phylogenetic relationships between and within the Avaritia species of the Palaeactic region with a special interest for the Obsoletus group at a world scale. Voucher specimens were selected based on morphology, sequenced for the CO1 region (mtDNA) and then slide-mounted allowing a morphological interpretation of the results afterwards. A total of 82 CO1 sequences including 43 sequences from the GenBank database were analyzed by Bayesian inference and the resulting tree was used to study species boundaries. The Barcoding gap was evaluated for the closest related species not supported by the species delimitation analysis. Within the Avaritia subgenus, we propose a new systematic scheme for the species of the Obsoletus group including C. scoticus as a basal clade with the two following complexes: the Sanguisuga complex with the species C. abchazicus, C. gornostaevae, C. sanguisuga and C. sinanoensis; the Obsoletus complex made of the species C. obsoletus, C. montanus and a new species. Culicoides filicinus, absent in this analysis, could not be placed in the proposed scheme. The existence of Dewulfi and Chiopterus complex is discussed. The results of the species boundaries analysis and the presence of discriminant morphological characters support the evidence of two new species under description with one in the Obsoletus complex. We also point out new records of C. gornostaevae (France, Sweden and Switzerland) and C. aff. sanguisuga (Sweden). The subgenus Avaritia includes worldwide major vectors of Orbivirus. The revealed diversity increases up to 10 species in western Europe and questions about the possible vector roles in Europe of these newly recorded species. Evaluating the vector role of the Avaritia species in bluetongue and other viruses transmission reaches a higher challenging level for the European teams. (Texte intégral

Analysis of ecological time series using state-space models

Prediction of population level responses to global change is the holy grail of population dynamics. Ecological time series provide incomplete snapshots of the state of a system and fitting dynamic models to such data necessitates the inclusion of stochastic elements to account for the influence of unmodeled processes. In ecology, state-space models (SSM) are used to couple stochastic dynamic models of populations (the "state-space") with models accounting for incomplete observation of underlying processes. Ecological SSMs are typically non-linear and non-Gaussian making conventional parameter estimation methods inapplicable. Markov chain Monte Carlo (MCMC) methods are widely used for parameter estimation of missing data problems, but it has not been obvious how to sample state-space trajectories and obtain efficient MCMC mixing for SSMs. Particle Markov chain Monte Carlo (PMCMC) algorithms were recently proposed as a solution to this problem (Andrieu, Doucet & Holstein et al. 2010). These algorithms utilise sequential Monte Carlo (a.k.a. particle filtering) to generate efficient proposal distributions that enable the sampling of state-space trajectories within standard MCMC routines -an advance that could potentially revolutionize ecological time series analysis. The French National Culicoides Surveillance Network has collected more than five million biting midges of 80 different species from 160 sites over 4 to 7 years. We explore the use of PMCMC to fit simple dynamic models to a relatively small subset of this data and attempt to assess the potential of upscaling to an analysis of the entire data set. We fit a number of different models with various levels of biological detail and seek a compromise between biological detail, computation time and predictive power. Implications of our results on ecological forecasting and the relative efficiency of PMCMC algorithms are discussed. (Texte intégral