A stochastic model to study rift valley fever persistence with different seasonal patterns of vector abundance: New insights on the endemicity in the tropical island of Mayotte

Rift Valley fever (RVF) is a zoonotic vector-borne disease causing abortion storms in cattle and human epidemics in Africa. Our aim was to evaluate RVF persistence in a seasonal and isolated population and to apply it to Mayotte Island (Indian Ocean), where the virus was still silently circulating four years after its last known introduction in 2007. We proposed a stochastic model to estimate RVF persistence over several years and under four seasonal patterns of vector abundance. Firstly, the model predicted a wide range of virus spread pat- terns, from obligate persistence in a constant or tropical environment (without needing verti- cal transmission or reintroduction) to frequent extinctions in a drier climate. We then identified for each scenario of seasonality the parameters that most influenced prediction variations. Persistence was sensitive to vector lifespan and biting rate in a tropical climate, and to host viraemia duration and vector lifespan in a drier climate. The first epizootic peak was primarily sensitive to viraemia duration and thus likely to be controlled by vaccination, whereas subsequent peaks were sensitive to vector lifespan and biting rate in a tropical cli- mate, and to host birth rate and viraemia duration in arid climates. Finally, we parameterized the model according to Mayotte known environment. Mosquito captures estimated the abundance of eight potential RVF vectors. Review of RVF competence studies on these species allowed adjusting transmission probabilities per bite. Ruminant serological data since 2004 and three new cross-sectional seroprevalence studies are presented. Transmis- sion rates had to be divided by more than five to best fit observed data. Five years after introduction, RVF persisted in more than 10% of the simulations, even under this scenario of low transmission. Hence, active surveillance must be maintained to better understand the risk related to RVF persistence and to prevent new introductions. (Résumé d'auteur

Absence of Evidence of Rift Valley Fever Infection in Eulemur fulvus (Brown Lemur) in Mayotte During an Interepidemic Period.

The potential role of Eulemur fulvus (brown lemur) in the epidemiology of Rift Valley fever (RVF) in Mayotte, during an interepidemic period, was explored. In February and March 2016, 72 animals were blood sampled and tested for RVF. No evidence of RVF genome or antibodies was found in the samples. The role of other wild mammals on the island should, however, be further investigated

Estimation of Rift Valley fever virus spillover to humans during the Mayotte 2018–2019 epidemic

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

Drivers for Rift Valley fever emergence in Mayotte: A Bayesian modelling approach

Rift Valley fever (RVF) is a major zoonotic and arboviral hemorrhagic fever. The conditions leading to RVF epidemics are still unclear, and the relative role of climatic and anthropogenic factors may vary between ecosystems. Here, we estimate the most likely scenario that led to RVF emergence on the island of Mayotte, following the 2006–2007 African epidemic. We developed the first mathematical model for RVF that accounts for climate, animal imports and livestock susceptibility, which is fitted to a 12-years dataset. RVF emergence was found to be triggered by the import of infectious animals, whilst transmissibility was approximated as a linear or exponential function of vegetation density. Model forecasts indicated a very low probability of virus endemicity in 2017, and therefore of re-emergence in a closed system (i.e. without import of infected animals). However, the very high proportion of naive animals reached in 2016 implies that the island remains vulnerable to the import of infectious animals. We recommend reinforcing surveillance in livestock, should RVF be reported is neighbouring territories. Our model should be tested elsewhere, with ecosystem-specific data

Etude des contacts entre élevages bovins voisins dans une zone de Bourgogne infectée de tuberculose par la méthode d'analyse des réseaux sociaux

La France a obtenu le statut officiellement indemne de tuberculose bovine en 2000. Depuis, la Côte-d'Or a fait face à une recrudescence du nombre de foyers qui ont été attribués à une contamination par le voisinage dans 35% des cas. Le but de cette étude était d'objectiver les caractéristiques du voisinage dans une zone infectée de tuberculose bovine en utilisant la méthode d'analyse des réseaux sociaux. Une enquête de terrain a été effectuée pour déterminer la fréquence et la distribution des contacts entre les élevages de la zone étudiée. Tous les contacts ne présentant pas le même risque pour la transmission de la tuberculose, une pondération a été effectuée. D'après cette pondération, les mouvements de bovins étaient le type de contact le plus à risque mais aucun n'est intervenu dans la zone pendant la période étudiée. Le contact apparaissant le plus fréquemment était le contact avec les sangliers, mais le risque associé à chaque contact est très faible. Les contacts directs entre bovins au pâturage et les contacts avec les latrines de blaireaux étaient moins fréquents mais étaient les plus à risque en raison de la probabilité de transmission de M.bovis à chaque contact. La structure de ces deux derniers réseaux était hétérogène du point de vue de la centralité (par le degré ou la proximité). En début d'évolution, cela devrait favoriser la circulation rapide de la maladie entre les élevages par rapport à une population homogène et parfaitement mélangée. Dans la zone, 95% des contacts étaient explicables par des contacts directs au pâturage, ou indirects via des blaireaux ou des sangliers. D'autres types de contacts intervenaient moins fréquemment (utilisation de matériel agricole en commun, divagation) voire pas du tout (participation à un rassemblement d'animaux). Les différentes modalités de contacts étaient liées entre elles mais aucune ne pouvait expliquer complètement les contacts de voisinage d'une exploitation, ce qui pose problème pour la mise en place de mesures de lutte.MAISONS-ALFORT-Ecole Vétérin (940462302) / SudocTOULOUSE-EN Vétérinaire (315552301) / SudocSudocFranceF