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Mosquitoes, major vectors of diseases, are sensitive to rainfall which is necessary for their immature aquatic stages, and to temperature which affects their development and life cycle dynamics. Climate change can therefore impact the transmission of vector-borne diseases such as malaria, the world's major parasitic disease causing over 600,000 deaths per year, and Rift Valley Fever (RVF), a zoonotic disease decimating herds, causing health risks and catastrophic economic losses in Africa.The Intergovernmental Panel on Climate Change (IPCC) report provides climate scenarios for the 21st century with different standard greenhouse gas emission scenarios, named Representative Concentration Pathway (RCP). By 2080, the risk of malaria transmission is estimated to decrease in the Sahel region and to increase in the East African Plateau as a result of rising temperatures under the RCP8.5 scenario. Although paleoclimate studies show that melting ice sheet can induce abrupt climate change, state of the art IPCC future projections do not consider such a potential rapid destabilisation of polar ice sheets. However, the West Antarctic and Greenland ice sheet are vulnerable to climate change and even a partial melting would cause major climatic changes, even in tropical regions. No study has yet quantified the impact of an abrupt melting of the ice sheets on the distribution of malaria and RVF. This work is based on future climate numerical simulations using the coupled global climate model IPSL-CM5A-LR with RCP8.5 as radiative forcing. Simulations of freshwater release, corresponding to the accelerated and partial melting of the polar ice sheets, were carried out with different melting assumptions:-for Greenland, a freshwater flux equivalent to a global sea level rise of 0.5m, 1m, 1.5m and 3m is released into the North Atlantic;-for Antarctica, a quantity of freshwater equivalent to a global sea level rise of 3m is released off its western part.These continuous water inputs are prescribed from 2020 to 2070.This study showed that the oceanic and atmospheric impacts of a partial melting of Greenland are stronger on the global climate, and particularly on monsoons, than those associated with the melting of West Antarctica, probably due to the effect of the circumpolar current. Subsequently, only scenarios considering a partial melting of Greenland were used to study their impacts on malaria. Simulated and/or observed temperature and precipitation were used to drive mathematical models of malaria transmission risk. Five mathematical malaria models were used. An accelerated melting of Greenland leads to a southward shift of the American and African monsoons. Malaria risk increases in southern Africa, decreases in the Sahel and increases moderately on the East African Plateau.For the study of RVF, the Liverpool Rift Valley Fever (LVRF) model was validated at country scale by comparing simulations driven by observed daily temperatures and rainfall from climate reanalyses with different health data sets. Then, a potential correlation between simulated RVF transmission risk and the main regional climate variability modes (ENSO and DMI) is shown over the Rift African region. The model correctly reproduces RVF epidemics in Kenya, Somalia and Zambia, and to a lesser extent in Senegal and Mauritania. RVF risk increases over the epidemic areas in East Africa during the El Niño phenomenon.; Les moustiques, vecteurs majeurs de maladies, sont sensibles aux précipitations nécessaires au développement de leurs stades immatures aquatiques, et aux températures qui conditionnent leur cycle de vie. Le changement climatique impacte la transmission des maladies vectorielles, telles que le paludisme, première maladie parasitaire mondiale, et la Fièvre de la Vallée du Rift (FVR), zoonose décimant les troupeaux, entraînant un risque sanitaire et causant des pertes économiques en Afrique.Les rapports du Groupe Intergouvernemental d'Experts du Climat (GIEC) présentent des projections climatiques pour le XXIème siècle avec différents scénarios d'émissions de gaz à effet de serre standards appelés « Representative Concentration Pathway » (RCP). Ceux-ci démontrent que d'ici 2080, avec le scénario RCP8.5, le risque de transmission du paludisme est estimé à la baisse dans la région du Sahel et à la hausse sur les plateaux est-africains, suite à l'augmentation des températures. Par ailleurs, les paléoclimats indiquent que la fonte des calottes de glace peut induire des changements climatiques abrupts. Cependant, les projections standards du GIEC ne considèrent pas une potentielle déstabilisation de ces calottes. L'Antarctique et le Groenland sont pourtant vulnérables aux dérèglements climatiques et une fonte rapide de ces calottes, même partielle, provoquerait des changements climatiques majeurs même en régions tropicales. Aucune étude n'avait jusque-là quantifié l'impact d'une fonte même partielle de celles-ci sur la distribution des moussons et sur le risque de transmission du paludisme et de la FVR en Afrique.Ce travail repose sur des simulations numériques du climat futur réalisées à partir du modèle climatique global couplé IPSL-CM5A-LR avec pour forçage radiatif le scénario RCP8.5. Des simulations de relâchement d'eau douce correspondant à la fonte accélérée et partielle des calottes polaires ont été réalisées avec différentes hypothèses de fonte :-pour le Groenland, un flux d'eau douce équivalent à une augmentation globale du niveau marin de 0.5, 1, 1.5 et 3m est libéré en Atlantique Nord ;-pour l'Antarctique, une quantité d'eau douce équivalente à une hausse globale du niveau des mers de 3m (fonte de tout l'Antarctique de l'Ouest) est relâchée au large de sa région Ouest.Ces apports d'eau douce ont lieu de 2020 à 2070, en flux continu.Cette étude a démontré que les impacts, océaniques et atmosphériques, liés à la fonte du Groenland sont plus forts sur le climat global, particulièrement sur les systèmes de mousson en Afrique, que ceux liés à la fonte de tout l'Ouest Antarctique, ce qui est certainement dû au courant circumpolaire. Par la suite, seuls les scénarios considérant une fonte partielle du Groenland ont été utilisés pour étudier leurs impacts potentiels sur le paludisme. Les températures et précipitations simulées et/ou observées permettent de piloter des modèles mathématiques du risque de transmission. Cinq modèles mathématiques de paludisme ont été utilisés. Une fonte accélérée du Groenland induit un décalage des zones de mousson américaines et africaines vers le sud. Le risque de paludisme augmente dans le sud de l'Afrique, diminue au Sahel et augmente modérément sur les plateaux d'Afrique de l'Est. Pour l'étude de la FVR, le modèle Liverpool Rift Valley Fever (LVRF) a été validé par pays en comparant les simulations, obtenues à partir des températures et précipitations journalières issues des réanalyses climatiques, avec différents jeux de données. Puis, un travail exploratoire a permis de déterminer une corrélation entre le risque de transmission simulé et les principaux modes de variabilité climatique régionaux (ENSO et DMI). Les résultats montrent que le modèle reproduit correctement les épidémies de FVR au Kenya, Somalie et Zambie, et plus modérément au Sénégal et en Mauritanie. Une augmentation du risque de FVR est montrée sur les zones épidémiques d'Afrique de l'Est lors du phénomène El Niño.

International audience; Rift Valley fever (RVF) is a major emerging arboviral disease with a complex epidemiological cycle. RVF virus (RVFV) is transmitted by mosquito vectors to ruminants, causing epizootics, and then from animals to humans, triggering epidemics. During its cycle, RVFV infects a wide range of hosts, but the associated pathogenesis has yet to be elucidated. RVFV displays a predominant hepatic tropism, but also has a multicellular tropism inducing physiopathological effects in several tissues. However, there is variability between species in terms of physiopathology : a common clinical picture is found (severe hepatitis, hemorrhages, leukopenia), but certain forms are mainly found in humans (neurological and ocular damage) or in ruminant herds (waves of abortions). Although the molecular mechanisms involved are still poorly understood, it seems that early inflammatory response is related to the severity of the pathology. A better understanding of the pathogenesis of RVFV seems essential, especially since no specific treatment exists to date.; La fièvre de la vallée du Rift (FVR) est une arbovirose émergente majeure possédant un cycle de transmission complexe. Le virus de la FVR (RVFV) est transmis aux élevages de ruminants par des moustiques vecteurs, provoquant des épizooties, puis de l’animal à l’Homme, déclenchant alors des épidémies. Au cours de son cycle, le RVFV infecte une large gamme d’hôtes, la pathogenèse associée soulevant de nombreuses questions. Malgré un tropisme principalement hépatique, le RVFV a également un tropisme multicellulaire induisant un effet physiopathologique dans de nombreux tissus. Un tableau clinique commun est habituellement retrouvé (hépatite sévère, hémorragies, leucopénie) mais une variabilité interspécifique a également été décrite. Ainsi, certaines formes sont principalement retrouvées chez l’Homme (atteintes neurologiques et oculaires) ou dans les élevages de ruminants (vagues d’avortements). Bien que les mécanismes moléculaires impliqués soient encore mal connus, il semblerait que la sévérité de la pathologie soit liée à la réponse inflammatoire précoce. De même, la pathogenèse du RVFV semble être soumise à de nombreux facteurs responsables d’une variabilité inter-individuelle importante dans la sévérité de l’infection. Devant l’absence de traitement spécifique, il semble primordial de mieux comprendre la pathogenèse du RVFV.

Rift Valley fever (RVF-V) is a viral, vector-borne, zoonotic disease. It affects multiple hosts, mainly livestock such as cattle, sheep, and goats. We aimed at enhancing knowledge on the relative contribution of host species to transmission, focusing on Senegal, a region with recurring RVFV circulation. With a systematic review of existing mechanistic models of RVFV transmission dynamics, we identified critical knowledge gaps and characterised the diversity of modelling approaches. We mapped RVF epidemic potential in northern Senegal for three consecutive rainy seasons (2014-2016), using the basic reproduction number. September was identified as a period of high risk of amplification following RVFV introduction. To quantify differences in infectiousness between host species, we developed the first within-host model of RVFV production by host cells, and estimated the relationship between host infectious viral loads and the probability to infect mosquitoes. The results showed that sheep were the most infectious host species, and that Aedes vectors were more likely to get infected than Culex when fed with similarly infectious bloodmeals. We incorporated this heterogeneity into a metapopulation model representing seasonal herd movements in northern Senegal. We quantified the delay between RVFV introduction through nomadic herds and infection of sedentary populations. We highlighted a systematic earlier infection in cattle than goats and sheep. This PhD used modeling to disentangle the complex transmission dynamics of a multi-host multivector pathogen, highlighting possible avenues for the development of efficient and targeted control strategies, crucial to ultimately prevent human cases.; La fièvre de la Vallée du Rift (FVR) est une maladie virale, vectorielle, et zoonotique. Elle touche principalement les animaux d’élevage : bovins, chèvres, moutons. Nous visions à mieux comprendre la contribution des différentes espèces d’hôtes à la transmission du virus de la FVR, en prenant comme zone d’étude le Sénégal. Une revue de la littérature nous a permis de caractériser la diversité des modèles mathématiques existants, et les questions que ces derniers n’ont pas encore abordé concernant la FVR. Nous avons ensuite cartographié le potentiel épidémique de la FVR au nord du Sénégal, et avons montré que pendant 3 saisons des pluies consécutives (2014-2016), le mois de Septembre était la période la plus à risque. Pour quantifier de potentielles différences d’infectiosité entre espèces d’hôtes à l’échelle individuelle, nous avons développé un modèle intra-hôte de la dynamique virale, et avons fait le lien avec la probabilité d’infecter les vecteurs. Nos résultats montrent que les moutons sont l’espèce la plus infectieuse, et que les moustiques du genre Aedes s’infectent plus facilement que les Culex. Enfin, nous avons incorporé cette hétérogéneité dans une métapopulation modélisant les mouvements de transhumance saisonniers au nord du Sénégal. Cela nous a permis de quantifier le délai entre l’introduction du virus de la FVR par les populations nomades et la propagation de l’infection chez les sédentaires. Nous avons également mis en évidence une infectionsystématiquement plus précoce chez les bovins que chez les petits ruminants. Cette thèse a ainsi permis de mieux comprendre la dynamique de transmission d’un pathogène multi-hôtes et d’identifier des pistes pourl’élaboration de stratégies de maitrise ciblées et efficaces.

International audience; In social species, the transmission and maintenance of infectious diseases depends on the contact patterns between individuals within groups and on the interactions between groups. In southern Africa, the Cape buffalo (Syncerus caffer caffer) is a vector for many pathogens that can infect sympatric livestock. Although intragroup contact patterns of Cape buffalo have been relatively well described, how groups interact with each other and risks for pathogen transmission remain poorly understood. We identified and compared spatial behavior and contact patterns between neighboring groups of Cape buffalo under contrasting environments: within the seasonally flooded environment of the Okavango Delta in Botswana and the semi-arid environment of northern Kruger National Park in South Africa. We used telemetry data collected between 2007 and 2015 from 10 distinct groups. We estimated seasonal overlap and proximity between home ranges of pairwise neighboring groups, and we quantified seasonal contact patterns between these groups. We defined contact patterns within variable spatiotemporal windows compatible with the transmission of diseases carried by the Cape buffalo: bovine tuberculosis, brucellosis, and Rift Valley fever (mosquito-borne transmission). We examined the effects of habitat and distance to water on contact location. In both study populations, neighboring buffalo groups were highly spatially segregated in the dry and rainy seasons. Inter-group contact patterns were characterized by very few direct and short-term indirect (within 0-2 days) contacts, lasting on average 1 hour and 2 hours, respectively. Contact patterns were generally consistent across populations and seasons, suggesting species-specific behavior. In the drier study site, the probability of indirect and vector-borne contacts generally decreased during the dry season with increasing distance to water. In the seasonally flooded area, only the probability of vector-borne contact decreased with increasing distance to water. Our results highlight the importance of dry season water availability in influencing the dynamics of indirectly transmitted Cape buffalo pathogens but only in areas with low water availability. The results from this study have important implications for future modeling of pathogen dynamics in a single host, and the ecology and management of Cape buffalo at the landscape level.

Estimating the epidemic potential of vector-borne diseases, along with the relative contribution of underlying mechanisms, is crucial for animal and human health worldwide. In West African Sahel, several outbreaks of Rift Valley fever (RVF) have occurred over the last decades, but uncertainty remains about the conditions necessary to trigger these outbreaks. We use the basic reproduction number (R0) as a measure of RVF epidemic potential in Northern Senegal, and map its value in two distinct ecosystems, namely the Ferlo and the Senegal river delta and valley. We consider three consecutive rainy seasons (July-November 2014, 2015 and 2016) and account for several vector and animal species. Namely, we parametrize our model with estimates of Aedes vexans arabiensis, Culex poicilipes, Culex tritaeniorhynchus, cattle, sheep and goats abundances. The impact of RVF virus introduction is assessed every week, in 4367 pixels of 3,5km2. The results of our analysis indicate that September was the month with highest epidemic potential in each study area, while at-risk locations varied between seasons. We show that decreased vector densities do not highly reduce R0 and that cattle immunity has a greater impact on reducing transmission than small ruminants immunity. The host preferences of vectors and the temperature-dependent time interval between their blood meals are crucial parameters needing further biological investigations.HighlightsSeptember is a period of high Rift Valley fever epidemic potential in northern Senegal regardless of the year, but exact locations where epidemics might start change between rainy seasons.Decreased vector densities during the rainy season did not highly reduce the epidemic potential of at-risk locations.High levels of immunity in cattle populations reduce more Rift Valley fever virus transmission than a high immunity in small ruminants in our study area. This aspect should be investigated further for targeted vaccination campaigns.Precise estimates of vector feeding preferences and the temperature-dependent lenght of their gonotrophic cycle are key to ensure a good detection of at-risk pixels.

Significance Rift Valley fever (RVF) is an emerging, zoonotic hemorrhagic fever, affecting mainly livestock and humans in Africa. Despite its growing global concern, the impact of control measures on epidemic dynamics using empirical data has not been assessed. By combining a unique RVF epidemic dataset covering both livestock and human data in a closed ecosystem (Mayotte island) with a dynamic model, we estimate viral transmission potential among livestock, and from livestock to humans. We also quantify the impact of vaccination in decreasing the epidemic size. We demonstrate that reactive livestock vaccination is key. We present a reference case study for RVF and illustrate the value of a One Health quantitative approach to surveillance and control of zoonotic infectious diseases., Rift Valley fever (RVF) is an emerging, zoonotic, arboviral hemorrhagic fever threatening livestock and humans mainly in Africa. RVF is of global concern, having expanded its geographical range over the last decades. The impact of control measures on epidemic dynamics using empirical data has not been assessed. Here, we fitted a mathematical model to seroprevalence livestock and human RVF case data from the 2018–2019 epidemic in Mayotte to estimate viral transmission among livestock, and spillover from livestock to humans through both direct contact and vector-mediated routes. Model simulations were used to assess the impact of vaccination on reducing the epidemic size. The rate of spillover by direct contact was about twice as high as vector transmission. Assuming 30% of the population were farmers, each transmission route contributed to 45% and 55% of the number of human infections, respectively. Reactive vaccination immunizing 20% of the livestock population reduced the number of human cases by 30%. Vaccinating 1 mo later required using 50% more vaccine doses for a similar reduction. Vaccinating only farmers required 10 times as more vaccine doses for a similar reduction in human cases. Finally, with 52.0% (95% credible interval [CrI] [42.9–59.4]) of livestock immune at the end of the epidemic wave, viral reemergence in the next rainy season (2019–2020) is unlikely. Coordinated human and animal health surveillance, and timely livestock vaccination appear to be key to controlling RVF in this setting. We furthermore demonstrate the value of a One Health quantitative approach to surveillance and control of zoonotic infectious diseases.

Cette étude est un financement du Projet Régional de Gestion Durable du Bétail Ruminant Endémique -PROGEBE- en Afrique de l’Ouest qui comprend la Guinée, le Mali, le Sénégal et la Gambie. En Guinée, plusieurs préfectures ont été couvertes dans les quatre régions naturelles du pays. Dans les sites primaires de Gaoual, Boké, Dinguiraye et Beyla, l’élevage est confronté à plusieurs pathologies parmi lesquelles les maladies de la reproduction. L’objectif de cette étude a été d’identifier et de déterminer la prévalence des maladies bactériennes, virales et parasitaires responsables des avortements afin de mettre en place des mesures prophylactiques. Les recherches ont été réalisées dans les villages ciblés au niveau des bovins destinés à la reproduction. Les pathogènes recherchés ont été Brucella abortus, Trichomonas foetus, Campylobacter spp. et le Virus de la Fièvre de la Vallée du Rift (FVR). Les techniques de séroagglutination : le Rose Bengale Test (RBT), la fixation du complément, la méthode directe de recherche des trichomonas, le May-Grünwald -Giemsa et l’Elisa indirecte pour la détection des anticorps IgM et IgG ont été utilisées pour la mise en évidence de ces agents étiologiques. Les résultats ont révélé que la brucellose atteint 11,75% des animaux et 42,31% des troupeaux villages. Les animaux examinés ont été indemnes de la trichomonose, de la campylobactériose et de la Fièvre de la Vallée du Rift., This study is funded by the Regional project for sustainable management of globally significant endemic ruminant livestock -PROGEBE- in West Africa, which includes Guinea, Mali, Senegal and Gambia. In Guinea, several prefectures were covered in the four natural regions of the country. In the primary sites of Gaoual, Boke, Dinguiraye and Beyla, livestock farming faces several pathologies including reproduction diseases. The objective of this study was to identify and determine the prevalence of bacterial, viral and parasitic responsible for abortions in order to implement prophylactic measures. The research was carried out in targeted villages involved in cattle breeding. The pathogens sought were Brucella abortus, Trichomonas fetus, Campylobacter spp. and the Rift Valley Fever Virus (RVF). Agglutination techniques (RBT), complement fixation, direct search method of trichomoniasis, the May-Grünwald Giemsa and indirect ELISA for the detection of IgM and IgG antibodies were used for the detection of these etiological agents. The results reveal that brucellosis affects11.75% and 42.31% of the villages’ herds. The animals examined were free of trichomoniasis, campylobacteriosis and Rift Valley Fever.

Rift Valley fever (RVF) is a mosquito-borne viral infection mostly encountered in Africa. In its acute form, it severely affects domestic and wild ruminants, dromedaries, and humans. It is considered as an emerging disease, with increased frequency in several regions, and a spread potential to many areas under the influence of two main drivers: environmental (including climatic) changes and animal mobility (livestock trade, transhumance). In this chapter, we discuss the peculiarities of RVF epidemiology in Sahelian Africa and we show how the joint influence of these two drivers may trigger RVF epidemics. The public health impact of RVF can be severe, with tens of thousands of human cases and hundreds of fatalities recorded during large epidemics. Beyond its direct, negative effects on public and animal health, RVF has large economic consequences related to bans on livestock importation from infected countries. Solutions are available to improve surveillance and control of RVF in Sahelian Africa according to well-defined, risk-based strategies. The implementation of coordinated actions between Public Health and Animal Health authorities would represent an important advance in the One Health joint approach of RVF for better prevention, early detection, and reaction.

SUMMARYA study was conducted to assess the awareness of cattle abortions due to brucellosis, Rift Valley fever (RVF) and leptospirosis, and to compare frequencies of reported abortions in communities living at the periphery of the Great Limpopo Transfrontier Conservation Area in southeastern Zimbabwe. Three study sites were selected based on the type of livestock–wildlife interface: porous livestock–wildlife interface (unrestricted); non-porous livestock–wildlife interface (restricted by fencing); and livestock–wildlife non-interface (totally absent or control). Respondents randomly selected from a list of potential cattle farmers (N = 379) distributed at porous (40·1%), non-interface (35·5%) and non-porous (26·4%), were interviewed using a combined close- and open-ended questionnaire. Focus group discussions were conducted with 10–12 members of each community. More abortions in the last 5 years were reported from the porous interface (52%) and a significantly higher per cent of respondents from the porous interface (P < 0·05) perceived wildlife as playing a role in livestock abortions compared with the other interface types. The odds of reporting abortions in cattle were higher in large herd sizes (odds ratio (OR) = 2·6; 95% confidence interval (CI) 1·5–4·3), porous (OR = 1·9; 95% CI 1·0–3·5) and non-porous interface (OR = 2·2; 95% CI 1·1–4·3) compared with livestock–wildlife non-interface areas. About 21·6% of the respondents knew brucellosis as a cause of abortion, compared with RVF (9·8%) and leptospirosis (3·7%). These results explain to some extent, the existence of human/wildlife conflict in the studied livestock–wildlife interface areas of Zimbabwe, which militates against biodiversity conservation efforts. The low awareness of zoonoses means the public is at risk of contracting some of these infections. Thus, further studies should focus on livestock–wildlife interface areas to assess if the increased rates of abortions reported in cattle may be due to exposure to wildlife or other factors. The government of Zimbabwe needs to launch educational programmes on public health awareness in these remote areas at the periphery of transfrontier conservation areas where livestock–wildlife interface exists to help mitigate the morbidity and mortality of people from some of the known zoonotic diseases.

International audience; Mosquitoes are vectors of major pathogen agents worldwide. Population dynamics models are useful tools to understand and predict mosquito abundances in space and time. To be used as forecasting tools over large areas, such models could benefit from integrating remote sensing data that describe the meteorological and environmental conditions driving mosquito population dynamics. The main objective of this study is to assess a process-based modeling framework for mosquito population dynamics using satellite-derived meteorological estimates as input variables. A generic weather-driven model of mosquito population dynamics was applied to Rift Valley fever vector species in northern Senegal, with rainfall, temperature, and humidity as inputs. The model outputs using meteorological data from ground weather station vs satellite-based estimates are compared, using longitudinal mosquito trapping data for validation at local scale in three different ecosystems. Model predictions were consistent with field entomological data on adult abundance, with a better fit between predicted and observed abundances for the Sahelian Ferlo ecosystem, and for the models using in-situ weather data as input. Based on satellite-derived rainfall and temperature data, dynamic maps of three potential Rift Valley fever vector species were then produced at regional scale on a weekly basis. When direct weather measurements are sparse, these resulting maps should be used to support policy-makers in optimizing surveillance and control interventions of Rift Valley fever in Senegal.

International audience; Understanding human and animal mobility patterns is a key to predict local and global disease spread. We analysed the nomad herds' movement network in a pilot area of northern Senegal and used exponential random graph models (ERGM) to investigate the reasons behind these movements. We interviewed 132 nomadic herders to collect information about nomad herd structures, movements, and reasons for taking specific routes or gathering in certain areas. We constructed a spatially explicit network with villages as the nodes and nomad herds' movements as the connecting edges. The final ERGM showed that node and edge attributes such as presence of cattle in the herd (odds ratio = 12, CI: 5.3, 27.3), morbidity (odds ratio = 3.6, CI: 2.3, 5.7), and lack of water (odds ratio = 2, CI: 1.3, 3.1) were important predictors of nomad herds' movements. This study not only provides valuable information for monitoring important livestock diseases such as Rift Valley Fever in Senegal, but also helps implement outreach, education, and intervention programs for other emerging and endemic diseases affecting nomadic herds.

Les fievres hemorragiques virales regroupent plusieurs viroses, potentiellement graves, avec un tableau clinique relativement stereotype, d’evolution biphasique. Apres une incubation de 2 a 21 jours, apparition d’un syndrome pseudo-grippal qui evolue au bout de quelques jours, de maniere imprevisible, chez une proportion variable de patients, vers un syndrome hemorragique avec choc. La transmission interhumaine s’effectue le plus souvent par contacts avec des liquides biologiques, surtout en presence de sang. La biologie de ces virus, leur epidemiologie et leur letalite sont tres variables. Pour toutes ces fievres hemorragiques virales, l’importance d’un diagnostic rapide reside plus dans la necessite d’interrompre les chaines de transmission que dans les possibilites therapeutiques, limitees aux traitements symptomatiques, a l’exception notable de la fievre de Lassa (efficacite probable de la ribavirine).

We report on the long-distance movements of subadult female buffalo within a Transfrontier Conservation Area in Africa. Our observations confirm that bovine tuberculosis and other diseases can spread between buffalo populations across national parks, community land, and countries, thus posing a risk to animal and human health in surrounding wildlife areas.

International audience; Les maladies animales ainsi que les zoonoses, maladies infectieuses transmises entre les animaux et les hommes, sont un problème socioéconomique et de santé publique à l’échelle mondiale. Surveiller et contrôler ces maladies impliquent d’identifier les zones à risque. Des cartes de ces zones peuvent être établies en utilisant l’évaluation multicritère spatialisée, une méthode récente, rapide à mettre en œuvre et rigoureuse. Encore peu connue des décideurs en santé animale et publique vétérinaire, cette méthode est adaptée aux régions qui ont accès à peu de données épidémiologiques fiables, comme les pays du Sud à faible revenu ou les régions encore indemnes. Les cartes sont construites avec les experts locaux des régions concernées. Elles présentent des indices de risque qui combinent les données géographiques et environnementales, les avis d’experts et les informations issues d’études ou d’enquêtes existantes. Ces cartes peuvent ensuite être utilisées pour mieux cibler la surveillance et le contrôle des maladies.

Rift Valley fever (RVF) is a vector-borne zoonosis, with a wide variety of potential competent vectors. During the last fifteen years, RVF caused tens of thousands of human cases, hundreds of human deaths and more than 100,000 domestic ruminant deaths in Africa and in the Arabic peninsula. After the first detection of RVF in Mayotte, an animal health surveillance network has been created in 2009, namely the SESAM. The aim of this PhD was to assess the epidemiological situation of Mayotte toward RVF in 2012-2013, to assess the persistence probability of RVF in the territory and to document farmers’ perceptions and health priorities. In 2012, RVF surveillance has been revised in order to partially renew the pool of the sentinel herds. The passive surveillance with systematic RVF detection assay on abortion and abnormal mortality was enforced. A continuous decrease in the seroprevalence was observed based on 2010-2013 data. During 2012-2013, a steady incidence rate of about 2 seroconversions per 100 animal-year was observed. This rate is much lower than the previous assessment of 18% during 2011. RVF virus was not detected in any of the 41 declared abortion cases. Surveillance performance criteria were discussed and assessed showing mainly an increase in data quality between 2010 and 2013. A SIR dynamic model was built based on vector knowledge and observed seroprevalence in Mayotte from 2008 to 2013. Estimated host-vector transmission rate was fivefold lower than expected according to current literature. Persistence probability, without reintroduction of viremic animals, was predicted to be 10% five years after virus introduction. Finally, health problem prioritization in Mayotte was studied through focus groups, gathering 164 farmers. The five main issues stated were: blackleg, ticks, a respiratory « fever/flu-like» syndrome, a dermatologic syndrome and diarrhoea. RVF was absent from the priority problems list in which abortions were ranked 9th. However abortions came first when « risk » criteria was taken into account, raising issues of cultural risk perceptions. Further surveillance and research using transdisciplinary approaches that mix mathematical modelling and the humanities should be continued with the view to assess more precisely reemergence probability in Mayotte and anticipate mitigating measures. Surveillance and research should also align with farmers’ expectations. The development of syndromic surveillance (abortion, death, etc.) requires strengthening surveillance network and identification data quality. Mayotte surveillance components should also be fully integrated within the regional and national schemes., La fièvre de la Vallée du Rift (FVR) est une zoonose due à un virus transmissible par une large variété de vecteurs. Au cours des quinze dernières années, elle a rendu malades des dizaines de milliers de personnes, entrainé des centaines de décès humains et provoqué la mort de plus de 100 000 ruminants domestiques en Afrique et dans la péninsule arabique. Suite à la découverte de la présence du virus à Mayotte, les autorités sanitaires, le Cirad (Centre de coopération internationale en recherche agronomique pour le développement) et les éleveurs ont créé en 2009 un système de surveillance en santé animale, le SESAM. L‘objectif de cette thèse était de faire un état des lieux de la situation épidémiologique de la FVR chez les ruminants à Mayotte en 2012-2013, d’évaluer les perspectives de persistance de la maladie et d’étudier les perceptions et les priorités des éleveurs vis-à-vis de cette maladie. En 2012, le fonctionnement du dispositif de surveillance de la FVR a été révisé avec un renouvellement partiel du groupe d’éleveurs sentinelles et un renforcement de la surveillance événementielle basée sur la recherche systématique de la FVR en cas d’avortement ou de mortalité anormale. Une baisse continue de la séroprévalence de 2010 à 2013 a été observée. En 2012-2013, le taux d’incidence est resté stable avec environ deux séroconversions pour 100 animaux-ans. Ce taux est très inférieur au taux d’incidence de 18% observé en 2011. Le virus de la FVR n’a été détecté dans aucun des prélèvements réalisés dans le cadre de la déclaration officielle des avortements chez les ruminants (n=41). Des critères d’évaluation de la performance du dispositif de surveillance ont été proposés et ont mis en évidence une amélioration de la qualité des données entre 2010 et 2013. Un modèle dynamique de type SIR a permis d’estimer le niveau de transmission hôte-vecteur attendu qui expliquerait au mieux la séroprévalence observée de 2008 à 2013 à Mayotte. La probabilité de transmission hôte-vecteur estimée par ce modèle est cinq fois plus faible qu’attendue. Dans ces conditions, la probabilité de persistance de la FVR, en l’absence de nouvelle introduction d’animaux virémiques reste inférieure à 10%, cinq ans après l’arrivée du virus. Enfin, la priorisation des problèmes sanitaires à Mayotte par une démarche d’épidémiologie participative et des réunions d’éleveurs a mis en évidence que les cinq problèmes spontanément rapportés comme les plus importants chez les bovins sont dans l’ordre le charbon symptomatique, les tiques, le syndrome « bavite-fièvre-grippe», le syndrome « dermatophilose-boutons » et la diarrhée. La FVR est absente de ce classement mais les avortements arrivent en 9ème position et à la première selon le critère de « risque ». La surveillance, et les approches interdisciplinaires de modélisation et de sciences humaines doivent être poursuivies pour évaluer plus précisément le risque de réémergence de la FVR à Mayotte et anticiper les réponses à y apporter. La surveillance doit aussi s’adapter aux attentes des éleveurs et développer l’approche syndromique ainsi que s’intégrer pleinement aux dispositifs régionaux et nationaux.