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Additional file 2: Table S6. Observed Culicoides abundance during the sampling campaign from 7 to 22 March 2018.

Additional file 1: Table S1. Model parameters for C. bolitinos. Table S2. Model parameters for C. enderleini. Table S3. Model parameters for C. grahamii. Table S4. Model parameters for C. imicola. Table S5. Model parameters for C. kibatiensis.

Les élevages bovins de La Réunion connaissent régulièrement des foyers de "bavites", appellation locale des maladies causées par les virus de la fièvre catarrhale ovine (bluetongue virus, BTV) et de la maladie hémorragique épizootique (epizootic hemorragic disease virus, EHDV), deux orbivirus transmis par des moucherons hématophages du genre Culicoides (Diptera : Ceratopogonidae). Plusieurs sérotypes de ces deux orbivirus circulent sur l'île et sont responsables de pertes économiques et de dégradations de l'état sanitaire du cheptel bovin. Parmi les 5 espèces de Culicoides décrites à La Réunion, Culicoides imicola, Culicoides bolitinos, Culicoides enderleini, Culicoides grahamii, et Culicoides kibatiensis, au moins les deux premières sont vectrices du BTV et de l'EHDV aux ruminants. Dans ce contexte, il paraît important de caractériser l'écologie et de préciser le rôle vectoriel des Culicoides à La Réunion. Ce travail vise à i) déterminer les facteurs environnementaux et climatiques qui gouvernent la présence et l'abondance de chaque espèce de Culicoides dans l'île ; ii) modéliser leurs dynamiques temporelles et spatio-temporelles ; iii) identifier les espèces potentiellement impliquées dans la transmission des deux orbivirus et caractériser la circulation de ces deux virus dans les populations locales de Culicoides. Un suivi longitudinal reposant sur des collectes bimensuelles de moucherons réalisées dans 11 sites durant 26 mois a permis de caractériser puis d'analyser avec des modèles statistiques de haie les dynamiques temporelles des différentes espèces de Culicoides afin d'identifier les paramètres environnementaux et climatiques qui les gouvernent. Ces modèles de dynamique ont ensuite été spatialisés en utilisant le logiciel Ocelet et validés en s'appuyant sur les données issues d'une large campagne de captures dans 101 sites répartis sur toute l'île. Enfin, la recherche de BTV et d'EHDV, effectuée par PCR (réaction en chaîne par polymérase) dans 1500 pools monospécifiques de Culicoides collectés lors du suivi longitudinal, a permis de détecter chacun des deux orbivirus chez 4 des 5 espèces de Culicoides : le BTV a été détecté chez toutes les espèces sauf C. grahamii et l'EHDV chez toutes les espèces sauf C. enderleini. Les travaux de cette thèse ont donc permis d'approfondir les connaissances sur la composante vectorielle de la fièvre catarrhale ovine et de la maladie hémorragique épizootique à La Réunion, et, en l'absence de méthodes de prévention comme la vaccination et de stratégies de contrôle des vecteurs, de développer des approches permettant de préciser le risque de transmission de ces deux virus.

Additional file 2: Table S1. Characteristics of trapping sites. Table S2. Temporal variables considered on mixed-effect negative binomial hurdle models. Table S3. Non-dynamic variables considered on mixed-effect negative binomial hurdle models.

Bluetongue and epizootic hemorrhagic disease viruses are recognized worldwide as important vector-borne viruses with major consequences on livestock trade and breed-ing. They are both transmitted by certain small hematophagous biting midge species belonging to the Culicoides genus, to cattle, sheep and goats. If the epidemiological sit-uation in epizootic territories has been recently widely studied after massive outbreaks in Europe, endemic areas have been neglected. In this presentation, we will review three studies implemented between 2016-2018 in La Réunion Island to give better in-sights to the local situation: (i) a virological and serological survey on cattle to identify the two virus dynamics and prevalence, (ii) an entomological study on Culicoides spe-cies diversity and seasonal dynamics, and (iii) a virus screening in Culicoides species to identify and characterize vector species of both viruses, the level of infection in wild species populations and virus dynamics in Culicoides populations. Altogether, these three studies helped to have a better understanding of the epidemiological situations in the island. Five Culicoides species are described on the island, presenting an altitudi-nal gradient and 4 species are implicated in both virus transmissions. Seasonal dynam-ics is particularly marked for 3 species. Therefore, bluetongue might be considered as an endemic disease with continuous virus circulation, limited clinical cases and high serological prevalence while Epizootic hemorrhagic disease appeared as an epizootic disease with seasonal transmission patterns.

Reunion Island regularly faces outbreaks of epizootic haemorrhagic disease (EHD) and bluetongue (BT), two viral diseases transmitted by haematophagous midges of the genus Culicoides (Diptera: Ceratopogonidae) to animals of economic importance such as cattle, sheep and goats. To date, five species of Culicoides are recorded in Reunion Island: Culicoides bolitinos, C. enderleini, C. grahamii, C. imicola, and C. kibatiensis. Although epizootics and Culi-coides diversity are already well documented, abundance and seasonality of the five species are not. According to a recent viral screening of local Culicoides populations (unpublished data), at least four species are involved in the transmission of each virus. Therefore, cha-racterizing the risk period by modelling the temporal dynamics of the five Culicoides species is a key step to better understand BT and EHD epidemiology and improve their control. Between 2016 and 2018, 55 biweekly Culicoides catches using OVI traps were set up in 11 sites. A hurdle model (i.e. a presence/absence model combined with an abundance model) was developed for each species in order to determine climatic and environmental drivers of presence and abundance of Culicoides. Regarding abundance, average Culicoides catch per site ranges from 4 to 45,875 individuals. Also, diversity differ between sites with C. imicola being dominant at low altitude and C. kiba-tiensis at high altitude. A marked seasonality is observed for the 3 other species. Eleven me-teorological and environmental determinants were used to model presence and abundan-ce of each species: temperature, humidity, rain, wind, global radiation, vegetation index, eco-climatic area, land use, farm density, animal density and length of nearby watercourse. The association of these determinants to explain presence and/or abundance depends on the species, but each plays a role in at least one species. This is the first study to model Culicoides population dynamics in Reunion Island. In the absence of vaccination and vector control strategies, determining periods of high abundance of Culicoides is a crucial first step towards identifying periods at high risk of transmission for both viruses.

Objectives: Bluetongue (BT) and epizootic hemorrhagic disease (EHD) viruses are two important vector-borne orbiviruses with a worldwide distribution that have major impacts on livestock breeding and trade. They are transmitted by hematophagous Culicoides species. If epidemiological investigations in epizootic territories conducted after massive outbreaks enabled to better understand the epidemiology of these diseases, their epidemiology remain poorly studied/understood in areas of endemicity. In this context, three studies were implemented in Reunion Island located in the South Western Indian Ocean Materials and Methods: The three studies were: (i) a virological and serological survey on cattle to identify BT and EHD viruses seasonal dynamics and prevalence, (ii) an entomological study on Culicoides species diversity, seasonal dynamics and spatial distribution, (iii) a viral screening in Culicoides species to identify and better characterize the vector species involved in the viral transmission, the level of infection in field populations and virus dynamics in Culicoides populations. Results: The period with highest levels of seroconversion occurred is the hot and rainy season, when incidence of antibody acquisition reached 36.7% (IC95% = [31.7%; 41.7%]) for EHD virus and 20.7% (IC95% = [16.3% ; 25.1%]) for BT virus. Five Culicoides species are described on the island, and seasonal dynamics is particularly marked for three of them. Four species are involved in the transmission of each virus. Conclusion: Overall, BT is endemic with continuous virus circulation, limited clinical cases and high serological prevalence while EHD is epizootic with a marked seasonal transmission pattern.

International audience

The hard ticks Amblyomma variegatum is the main vector of Ehrlichia ruminantium which is the pathogen responsible for heartwater or cowdriosis, a disease of ruminants. This tick originates from sub-Saharan Africa and is now widely widespread. A. variegatum has been described in 1899 for the first time in Madagascar, but its introduction is probably older and very likely concomitant with livestock introduction from Africa. A. variegatum has also been described in the Comoros, Mayotte, La Reunion and Mauritius islands. The aim of this study was to investigate the genetic and demographic phenomena that have shaped the present distribution and structure of A. variegatum populations in the Indian Ocean area. A first phylogeographic approach has been carried out, by analysing two mitochondrial-DNA genes at an intra-specific level through the analysis of tick samples from Madagascar and from the other Indian Ocean Islands included in this study. These samples have been compared to samples from Africa, where this species is originated from, and samples from the French West Indies where A. variegatum was introduced around the 18th century. This study will help to elucidate A. variegatum introduction history in the different Indian Ocean Islands. A population genetics approach, using microsatellite markers, focused on Madagascar and some other islands (La Reunion, Comoros and Mayotte islands), has given an insight into the present population structure. This study has led to two main lineages identification: one covering all the species distribution and one restricted to East Africa and Indian Ocean area. These two lineages are in sympatry in Madagascar. The results seemed to be in keeping with the historical data concerning the introduction of the tick in the Indian Ocean area. In Madagascar, a high genetic diversity has been described whereas a lower genetic diversity is observed in the other islands. In Madagascar tick populations are clearly structured but in a heterogeneous way. This structure is probably shaped by the complex interaction of geographic, climatic and anthropic factors. (Texte intégral)

Une synthèse des connaissances sur l'écologie, l'importance épidémiologique et le contrôle des stomoxes à l'île de la Réunion est présentée. L'intensification de l'élevage bovin dans ce département a créé des conditions optimales pour la pullulation de ces insectes hématophages. Les stomoxes sont non seulement une nuisance directe par la spoliation sanguine et le stress lié au harcèlement des animaux, mais aussi et surtout une nuisance indirecte, en tant que vecteurs mécaniques de nombreuses maladies animales. À la Réunion, le principal rôle pathogène des stomoxes est la transmission de l'anaplasmose bovine, qui est une contrainte sanitaire majeure pour l'élevage de races européennes. Des études récentes ont permis de mieux appréhender leur distribution, leur dynamique et leur structure de populations, mais leur contrôle, organisé par le Groupement de Défense Sanitaire, reste problématique. Les, essais mis en place depuis 1994, ont donné des résultats variables ; les perspectives sont discutées. De nombreuses pistes de recherche sont explorées pour mieux comprendre leur rôle dans la transmission mécanique immédiate ou différée des agents pathogènes. L'amélioration de leur contrôle pourra être assurée en mettant en place une politique de gestion intégrée à l'échelle de l'île, basée sur une meilleure prise en compte des connaissances sur leur écologie et sur l'intégration de nouvelles méthodes de lutte (pédiluves, champignons entomopathogènes, moustiquaires imprégnées).

BackgroundReunion Island regularly faces outbreaks of epizootic haemorrhagic disease (EHD) and bluetongue (BT), two viral diseases transmitted by haematophagous midges of the genusCulicoides(Diptera: Ceratopogonidae) to ruminants. To date, five species ofCulicoidesare recorded in Reunion Island in which the first two are proven vector species:Culicoides bolitinos,C. imicola,C. enderleini,C. grahamiiandC. kibatiensis. Meteorological and environmental factors can severely constrainCulicoidespopulations and activities and thereby affect dispersion and intensity of transmission ofCulicoides-borne viruses. The aim of this study was to describe and predict the temporal dynamics of allCulicoidesspecies present in Reunion Island.MethodsBetween 2016 and 2018, 55 biweeklyCulicoidescatches using Onderstepoort Veterinary Institute traps were set up in 11 sites. A hurdle model (i.e. a presence/absence model combined with an abundance model) was developed for each species in order to determine meteorological and environmental drivers of presence and abundance ofCulicoides.ResultsAbundance displayed very strong heterogeneity between sites. AverageCulicoidescatch per site per night ranged from 4 to 45,875 individuals.Culicoides imicolawas dominant at low altitude andC. kibatiensisat high altitude. A marked seasonality was observed for the three other species with annual variations. Twelve groups of variables were tested. It was found that presence and/or abundance of all fiveCulicoidesspecies were driven by common parameters: rain, temperature, vegetation index, forested environment and host density. Other parameters such as wind speed and farm building opening size governed abundance level of some species. In addition,Culicoidespopulations were also affected by meteorological parameters and/or vegetation index with different lags of time, suggesting an impact on immature stages. Taking into account all the parameters for the final hurdle model, the error rate by Normalized Root mean Square Error ranged from 4.4 to 8.5%.ConclusionsTo our knowledge, this is the first study to modelCulicoidespopulation dynamics in Reunion Island. In the absence of vaccination and vector control strategies, determining periods of high abundance ofCulicoidesis a crucial first step towards identifying periods at high risk of transmission for the two economically important viruses they transmit.