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National audienc
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Rift Valley fever (RVF) is a mosquito-borne disease mostly affecting wild and domestic ruminants. It is widespread in Africa, with spillovers in the Arab Peninsula and the southwestern Indian Ocean. Although RVF has been circulating in... more
Rift Valley fever (RVF) is a mosquito-borne disease mostly affecting wild and domestic ruminants. It is widespread in Africa, with spillovers in the Arab Peninsula and the southwestern Indian Ocean. Although RVF has been circulating in West Africa for more than 30 years, its epidemiology is still not clearly understood. In 2013, an RVF outbreak hit Senegal in new areas that weren’t ever affected before. To assess the extent of the spread of RVF virus, a national serological survey was implemented in young small ruminants (6–18 months old), between November 2014 and January 2015 (after the rainy season) in 139 villages. Additionally, the drivers of this spread were identified. For this purpose, we used a beta-binomial (BB) logistic regression model. An Integrated Nested Laplace Approximation (INLA) approach was used to fit the spatial model. Lower cumulative rainfall, and higher accessibility were both associated with a higher RVFV seroprevalence. The spatial patterns of fitted RVFV ...
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Bluetongue virus (BTV) (Reoviridae: Orbivirus) is a good example of emerging arbovirus in Europe, with a little understanding of the disease epidemiology. This virus is transmitted by blood-sucking midges of the genus Culicoides (Diptera:... more
Bluetongue virus (BTV) (Reoviridae: Orbivirus) is a good example of emerging arbovirus in Europe, with a little understanding of the disease epidemiology. This virus is transmitted by blood-sucking midges of the genus Culicoides (Diptera: Ceratopogonidae) to wild and domestic ruminants. In Europe, BT had been considered as an exotic disease until recently. In 1998, several BT incursions were observed in the western Mediterranean Basin in line with the northward progression of C. imicola populations, the main afrotropical vector. From August 2006, the emergence and transmission of BT serotype 8 in northern Europe, in areas where C. imicola was absent, revealed the importance of autochthonous Culicoides species and the urgent need to understand their vector role. The emergence and massive spread of bluetongue virus in western Europe during 2006-2008 had disastrous consequences for sheep and cattle production and confirmed the ability of Palaearctic Culicoides to transmit the virus. De...
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a SAS Nevantropic, 16 bis av. du 14 juillet, 97300 Cayenne, French Guiana. b CIRAD (French Agricultural Research Center for Internationa l Development), Baillarguet Campus, 34398 Montpellie r Cedex. c UMR TETIS (Territories, Environment,... more
a SAS Nevantropic, 16 bis av. du 14 juillet, 97300 Cayenne, French Guiana. b CIRAD (French Agricultural Research Center for Internationa l Development), Baillarguet Campus, 34398 Montpellie r Cedex. c UMR TETIS (Territories, Environment, Remote Sensing and Spatial Information Joint Research Unit), Maison de la Téléd étection, 500 rue J.-F. Breton, 34093 Montpellier C edex 5, France. d IRD (Institut de Recherche pour le Développement ), 34394 Montpellier Cedex 05, France. e ISRA/LNERV Route du front de terre, BP 2057, Dak ar-Hann, Sénégal.
Research Interests: Geography and Population
Several animal or zoonotic emerging infectious disease (EID) events were recently caused by vector-borne pathogens, e.g. bluetongue virus (BTV) transmitted by biting midges which caused huge economic losses in western Europe between 2006... more
Several animal or zoonotic emerging infectious disease (EID) events were recently caused by vector-borne pathogens, e.g. bluetongue virus (BTV) transmitted by biting midges which caused huge economic losses in western Europe between 2006 and 2009, and is still around, or tick-borne encephalitis in northern and central Europe, causing several thousands of clinical cases in humans. The effects of climate changes have been put forward to explain these EID events. Because the bio-ecological features of arthropod vectors make them highly sensitive to environmental conditions, vector-borne diseases are ideal candidates to assess the effect of climate changes on EID. The question was extensively studied these past years. For instance, the effects of climate on BTV's emergence in Europe were evaluated by integrating high-resolution climate observations and model simulations within a climate-driven, mechanistic transmission model of BTV. This model explained, in both space and time, many...
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We have developed an explicit spatial and temporal model to predict the population dynamics and dispersal of the two main mosquito vector species (Aedes vexans and Culex poicilipes) involved in Rift Valley fever virus (RVFV) transmission... more
We have developed an explicit spatial and temporal model to predict the population dynamics and dispersal of the two main mosquito vector species (Aedes vexans and Culex poicilipes) involved in Rift Valley fever virus (RVFV) transmission in Senegal (western Africa). Covering an area of 11x10 km around the village of Barkedji, and located in the Ferlo valley (Northern Senegal), the study area is characterized by a complex and dense network of water bodies and ponds that are filled by rainfall during the rainy season (from July to mid- October). These water bodies are known to be the principal mosquito breeding sites in the area. A spatial diffusion model (Raffy and Tran, 2005) is applied in combination with a vector population dynamic model (Soti et al., 2009), and which takes into account the hydrological conditions of the system (Soti et al., submitted). The vector population dynamic model has been more specifically derived from Porphyre et al. (2005). Daily mosquito abundance for ...
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In the dominant livestock systems of Sahelian countries herds have to move across territories. Their mobility is often a source of conflict with farmers in the areas crossed, and helps spread diseases such as Rift Valley Fever. Knowledge... more
In the dominant livestock systems of Sahelian countries herds have to move across territories. Their mobility is often a source of conflict with farmers in the areas crossed, and helps spread diseases such as Rift Valley Fever. Knowledge of the routes followed by herds is therefore core to guiding the implementation of preventive and control measures for transboundary animal diseases, land use planning and conflict management. However, the lack of quantitative data on livestock movements, together with the high temporal and spatial variability of herd movements, has so far hampered the production of fine resolution maps of animal movements. This paper proposes a general framework for mapping potential paths for livestock movements and identifying areas of high animal passage potential for those movements. The method consists in combining the information contained in livestock mobility networks with landscape connectivity, based on different mobility conductance layers. We illustrate...
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In Senegal, the last epidemic of African horse sickness (AHS) occurred in 2007. The western part of the country (the Niayes area) concentrates modern farms with exotic horses of high value and was highly affected during the 2007 outbreak... more
In Senegal, the last epidemic of African horse sickness (AHS) occurred in 2007. The western part of the country (the Niayes area) concentrates modern farms with exotic horses of high value and was highly affected during the 2007 outbreak that has started in the area. Several studies were initiated in the Niayes area in order to better characterize Culicoides diversity, ecology and the impact of environmental and climatic data on dynamics of proven and suspected vectors. The aims of this study are to better understand the spatial distribution and diversity of Culicoides in Senegal and to map their abundance throughout the country. Culicoides data were obtained through a nationwide trapping campaign organized in 2012. Two successive collection nights were carried out in 96 sites in 12 (of 14) regions of Senegal at the end of the rainy season (between September and October) using OVI (Onderstepoort Veterinary Institute) light traps. Three different modeling approaches were compared: th...
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Several epidemics caused by different bluetongue virus (BTV) serotypes occurred in European ruminants since the early 2000. Studies on the spatial distribution of these vector-borne infections and the main vector species highlighted... more
Several epidemics caused by different bluetongue virus (BTV) serotypes occurred in European ruminants since the early 2000. Studies on the spatial distribution of these vector-borne infections and the main vector species highlighted contrasted eco-climatic regions characterized by different dominant vector species. However, little work was done regarding the factors associated with the velocity of these epidemics. In this study, we aimed to quantify and compare the velocity of BTV epidemic that have affected different European countries under contrasted eco-climatic conditions and to relate these estimates to spatial factors such as temperature and host density. We used the thin plate spline regression interpolation method in combination with trend surface analysis to quantify the local velocity of different epidemics that have affected France (BTV-8 2007-2008, BTV-1 2008-2009), Italy (BTV-1 2014), Andalusia in Spain (BTV-1 2007) and the Balkans (BTV-4 2014). We found significant di...
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Demographic rates (i.e., fecundity, mortality, offtake and intake rates) are necessary for assessing animal productivity and modeling the dynamics of tropical livestock populations. These rates are estimated from data collected in the... more
Demographic rates (i.e., fecundity, mortality, offtake and intake rates) are necessary for assessing animal productivity and modeling the dynamics of tropical livestock populations. These rates are estimated from data collected in the field. In developing countries, data collection and management is a tricky part of the studies. In that context, we present two standardized survey methods for ruminants and camels managed in extensive or semi-extensive farming systems. These methods can be adapted to many contexts (animal production and health, genetics or agricultural economy) and are provided with operational tools for data management and analysis. The first method, LASER, is based on longitudinal follow-up of herd with individual identification of the animals. Gold-standard of the on-farm methods, LASER is well adapted for accurate assessment of herd productivity and impact of new technologies (vaccine, reproduction,...). The second method, 12MO, is a rapid appraisal method based o...
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Figure S1. Poisson model of the impact of cattle footbath treatments on tsetse total catches in Chad. doi:10.1371/journal.pone.0067580.s001 (a) comparison of the predicted and observed values, (b) comparison of the random effects related to the intercept of the Poisson model to a normal distribut...more
Research Interests: Biology, Medicine, Multidisciplinary, Senegal, Multivariate Analysis, and 15 moreFemale, Animals, Poisson regression, Temperature, Paysage, PLoS one, Ruminant, Reproducibility of Results, Culicoides, CERATOPOGONIDAE, Species Specificity, Overdispersion, Modèle mathématique, Humidité, and Distribution spatiale
Research Interests: Biology, Medicine, Senegal, Biological Sciences, Equidae, and 15 moreSheep, Circadian Rhythm, Female, Animals, Horses, Biologie Animale, Culicoides, CERATOPOGONIDAE, African Horse Sickness, Orbivirus, Insect Vectors, Bluetongue virus, African horse sickness virus, Argasidae, and Medical and Health Sciences
Background In Senegal, the 2007 epidemic of African horse sickness (AHS) caused the death of 1,169 horses and considerable economic loss (Akakpo et al. 2011). The vectors responsible for biological transmission of the virus belong to the... more
Background In Senegal, the 2007 epidemic of African horse sickness (AHS) caused the death of 1,169 horses and considerable economic loss (Akakpo et al. 2011). The vectors responsible for biological transmission of the virus belong to the genus Culicoides (Diptera: Ceratopogonidae). In Senegal, studies on Culicoides are rare, out of date and did not specifically target the species in the vicinity of horses. Thus we initiated two studies in 2011 to better understand the dynamics and distribution of the Culicoides of Senegal and their involvement in the transmission of AHS virus (AHSV).
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Definitions are presented for a given cell or aggregation of cells. Calculations are the same for parturitions and abortions. We only describe the first.
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In the discrete-time approach, demographic rates are estimated from grouped data built using the “Lexis diagram” (Fig. 2.1), that was originally designed for human demography. This diagram plots three types of information simultaneously:... more
In the discrete-time approach, demographic rates are estimated from grouped data built using the “Lexis diagram” (Fig. 2.1), that was originally designed for human demography. This diagram plots three types of information simultaneously: the date of birth of an individual, its age and the time. The life history of each individual is represented in the plane “time × age” by a linear segment joining the entry and the exit of the individual (e.g. from birth to death). The paternity of the Lexis diagram is multiple [37]. Main contributions were provided by demographers of the nineteenth century (Karl Becker and Wilhelm Lexis in Germany, and Abraham Verweij in The Netherlands). Enhancements were then proposed from 1960 by the French demographer Rolland Pressat [38, 39].
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Restricted application of insecticides to cattle is a cheap and safe farmer-based method to control tsetse. In Western Africa, it is applied using a footbath, mainly to control nagana and the tick Amblyomma variegatum. In Eastern and... more
Restricted application of insecticides to cattle is a cheap and safe farmer-based method to control tsetse. In Western Africa, it is applied using a footbath, mainly to control nagana and the tick Amblyomma variegatum. In Eastern and Southern Africa, it might help controlling the human disease, i.e., Rhodesian sleeping sickness as well. The efficiency of this new control method against ticks, tsetse and trypanosomoses has been demonstrated earlier. The invention, co-built by researchers and farmers ten years ago, became an innovation in Burkina Faso through its diffusion by two development projects.
Research Interests: Biology, Agriculture, Medicine, Biological Sciences, Insecticides, and 15 moreHumans, Risk Perception, Livestock, Burkina Faso, Animals, Individual variation, Insecticide, Cattle, FARMING SYSTEM, Human Disease, Economic Benefit, Control Method, Insect Control, cattle diseases, and Medical and Health Sciences
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Tsetse flies are the cyclical vectors of deadly human and animal trypanosomes in sub-Saharan Africa. Tsetse control is a key component for the integrated management of both plagues, but local eradication successes have been limited to... more
Tsetse flies are the cyclical vectors of deadly human and animal trypanosomes in sub-Saharan Africa. Tsetse control is a key component for the integrated management of both plagues, but local eradication successes have been limited to less than 2% of the infested area. This is attributed to either resurgence of residual populations that were omitted from the eradication campaign or reinvasion from neighboring infested areas. Here we focused on Glossina palpalis gambiensis, a riverine tsetse species representing the main vector of trypanosomoses in West Africa. We mapped landscape resistance to tsetse genetic flow, hereafter referred to as friction, to identify natural barriers that isolate tsetse populations. For this purpose, we fitted a statistical model of the genetic distance between 37 tsetse populations sampled in the region, using a set of remotely sensed environmental data as predictors. The least-cost path between these populations was then estimated using the predicted fri...
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Risk assessment can be either quantitative, i.e. providing a numeric estimate of the probability of risk and the magnitude of the consequences, or qualitative, using a descriptive approach. The French Agency for Food, Environmental and... more
Risk assessment can be either quantitative, i.e. providing a numeric estimate of the probability of risk and the magnitude of the consequences, or qualitative, using a descriptive approach. The French Agency for Food, Environmental and Occupational Health and Safety (ANSES), formerly the French Food Safety Agency (AFSSA), bases its assessments on the opinions of scientific panels, such as the ANSES Animal Health Scientific Panel (AH-SP). Owing to the lack of relevant data and the very short period of time usually allowed to assess animal health risks on particular topics, this panel has been using a qualitative risk method for evaluating animal health risks or crises for the past few years. Some experts have drawn attention to the limitations of this method, such as the need to extend the range of adjectives used for the lower probabilities and to develop a way to assess consequences. The aim of this paper is to describe the improved method now established by the AH-SP, taking into ...
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In Burkina Faso, we assessed the efficacy of treating cattle with a footbath containing aqueous formulations of pyrethroids to control two tsetse-fly species, Glossina tachinoides Westwood, 1850 (Diptera, Glossinidae) and Glossina... more
In Burkina Faso, we assessed the efficacy of treating cattle with a footbath containing aqueous formulations of pyrethroids to control two tsetse-fly species, Glossina tachinoides Westwood, 1850 (Diptera, Glossinidae) and Glossina palpalis gambiensis Vanderplank 1949. Legs were the most targeted parts of the body for tsetse-fly blood meals: 81% (95% CI: 73, 89) for G. tachinoides and 88% (81, 95) for G. palpalis. The in-stable efficacy of footbath treatments was compared with manual full spraying with a 0.005% alphacypermethrin (Dominex, FMC, Philadelphia, USA) formulation (250mL versus 2L). The proportions of knocked-down flies were the same with footbath and full spray but the latter was more protective against fly bites. In field use, the efficacy of both methods should be similar given the recommended treatment frequency: 3 days for footbath versus 7 days for full spray. Among 96 cattle drinking at the same water point in Dafinso (Burkina Faso), 68 (71%) were treated with a foot...
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Factors related to the distribution of clinical bovine mastitis between rear and front quarters were studied using data from a 4 year survey of commercial dairy herds in western France. The study involved 844 mastitis cases affecting 597... more
Factors related to the distribution of clinical bovine mastitis between rear and front quarters were studied using data from a 4 year survey of commercial dairy herds in western France. The study involved 844 mastitis cases affecting 597 lactations of 500 French Friesian cows from 44 herds. Risk factor hypotheses were related to certain aspects of lactation, udder conformation and management practices. Distribution was modelled using a hierarchical logistic regression. Rear quarters were affected in 61.9% of cases. The only significant risk factor was the cow's parity; rear quarter clinical mastitis was more frequent in primiparous than in multiparous cows. In this retrospective study, udder conformation did not seem to play a significant role in mastitis distribution. No overdispersion parameter was observed, indicating that each mastitis case could be considered as an independent event.
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In Chad, in 1993-1994, investigation into "peste des petits ruminants" (PPR) outbreaks were carried out in flocks of Sahelian goats. Although in the early 1993 outbreaks the virus had not been isolated yet, a serological... more
In Chad, in 1993-1994, investigation into "peste des petits ruminants" (PPR) outbreaks were carried out in flocks of Sahelian goats. Although in the early 1993 outbreaks the virus had not been isolated yet, a serological prevalence (34%) was observed using ELISA test in 475 sera collected in the infested area. The virus was then isolated for the first time in Chad and typical PPR cases were observed in Sahelian goats, known to be little sensitive to the virus. To experimentally induce the disease, goats were inoculated with suspensions of lymph nodes or lungs, collected from sick animals. Lung suspensions induced the most serious symptoms. Suspensions of lungs and mesenteric lymph nodes were positive by agar-gel immunodiffusion test against PPR anti-serum, while prescapular lymph nodes remained negative. Characterization of the isolated virus, in particular with regard to its genomic identity, should be investigated.
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The authors describe the methodology used in an ecopathological survey of goat pneumopathies in periurban area of N'Djamena (Chad) during the dry, cold season of 1991-1992. The choice of farms was made after a typology survey. A total... more
The authors describe the methodology used in an ecopathological survey of goat pneumopathies in periurban area of N'Djamena (Chad) during the dry, cold season of 1991-1992. The choice of farms was made after a typology survey. A total of 3,500 small ruminants (85% of goats) belonging to 60 farms were identified and the performance and health of the animals examined from August 1991. The protocol used for collecting information and the strategy applied to the analysis of data were based on conceptual pre-models of analysis corresponding to the 3 observations scales used, i.e. goat, concession flock, day flock. The survey took place from December 1991 to March 1992. The difficulties of the statistical interpretation of the data, are emphasized. The biological significance of the risk factors is discussed. Measures for obtaining improvements should take into account the cost/profit ratio and the technical and financial possibilities of the farmers.
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A goat herd follow-up and an ecopathological survey on respiratory diseases were undertaken in Chad. Late puberty and high mortality were highlighted by the follow-up. Diseases were frequent and depended on the season. Few risk factors of... more
A goat herd follow-up and an ecopathological survey on respiratory diseases were undertaken in Chad. Late puberty and high mortality were highlighted by the follow-up. Diseases were frequent and depended on the season. Few risk factors of respiratory diseases were shown by the ecopathological survey. Mortality was connected with 3 parasitic and infectious factors. Decreasing the age at puberty and the mortality rate are priorities. Measures to achieve these aims are well known. They must be set up within a development program, in interaction with research, for a good use by the goat farmer.
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Epidemiological investigation on Rift Valley fever in small ruminants was carried out in Southern Mauritania after 1988 rainy season. Relationships were found between the incidence rate and the edaphic and climatic parameters.... more
Epidemiological investigation on Rift Valley fever in small ruminants was carried out in Southern Mauritania after 1988 rainy season. Relationships were found between the incidence rate and the edaphic and climatic parameters. Propositions are made to study epidemiology of this disease in this area.
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The importance of rainfall for the development of Aedes vexans arabiensis populations, one of the potential vectors of Rift Valley Fever in West Africa, was demonstrated in a two-year follow-up study conducted in the Ferlo region of... more
The importance of rainfall for the development of Aedes vexans arabiensis populations, one of the potential vectors of Rift Valley Fever in West Africa, was demonstrated in a two-year follow-up study conducted in the Ferlo region of Senegal. In 2003, the rainy season began with heavy rains and, as a result, temporary ponds, the breeding places for mosquitoes, were flooded at their maximum level immediately. In such conditions, Aedes vexans arabiensis populations are abundant at the very beginning of the season, when the majority of eggs in quiescence are flooded. Females, hatching from eggs laid the year before, quickly lay eggs on the pond's wet soil, which will undergo dormancy as the water level goes down. Rainless periods longer than seven days, the time needed for embryogenesis, followed by significant rainfall, will result in the hatching of very large numbers of new eggs. Thus, several generations of adults may exist during the same rainy season. Because of potential vert...