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SUMMARYThe objective of this study was to assess the performance of several algorithms for outbreak detection based on weekly proportions of whole carcass condemnations. Data from one French slaughterhouse over the 2005–2009 period were used (177 098 slaughtered cattle, 0.97% of whole carcass condemnations). The method involved three steps: (i) preparation of an outbreak-free historical baseline over 5 years, (ii) simulation of over 100 years of baseline time series with injection of artificial outbreak signals with several shapes, durations and magnitudes, and (iii) assessment of the performance (sensitivity, specificity, outbreak detection precocity) of several algorithms to detect these artificial outbreak signals. The algorithms tested included the Shewart p chart, confidence interval of the negative binomial model, the exponentially weighted moving average (EWMA); and cumulative sum (CUSUM). The highest sensitivity was obtained using a negative binomial algorithm and the highest specificity with CUSUM or EWMA. EWMA sensitivity was too low to select this algorithm for efficient outbreak detection. CUSUM's performance was complementary to the negative binomial algorithm. The use of both algorithms on real data for a prospective investigation of the whole carcass condemnation rate as a syndromic surveillance indicator could be relevant. Shewart could also be a good option considering its high sensitivity and simplicity of implementation.

National audience; This article is aimed at discussing the feasibility and advantages of using artificial insemination data, through a new indicator of mid-term abortions, the mid-term abortion incidence rate, in order to identify the impact of an abortive event retrospectively or prospectively. Two studies are used to illustrate the purpose, based on the analysis of mid-term abortion incidence rate to estimate the impact of the Bluetongue serotype 8 (BT8) epizootic that emerged in France in 2006 and then spread across the country in 2007 and 2008. The first study was a retrospective analysis of the temporal variations of the mid-term abortion incidence rate in each French department enabled to identify a posteriori the impact of BT8 on abortion occurrence. The second study was based on a weekly analysis of the temporal variations of the mid-term abortion incidence rate, and showed that the impact of BT8 would have been identified 12 weeks after the occurrence of the disease in 50% of the departments. These results suggest that there is a need to study the feasibility to implement an integrated surveillance of bovine abortions, based on the mandatory notification of bovine abortions (i.e. the current surveillance system with some improvements) and a syndromic surveillance system (that should be implemented at a lower level than the department, to improve timeliness).; Le présent article a pour objectif de discuter de la faisabilité et de l’intérêt que représenterait le suivi d’un indicateur indirect de survenue des avortements élaboré à partir des données d’insémination artificielle, le taux d’avortements précoces, afin d’identifier l’impact d’un évènement abortif, de manière rétrospective ou prospective. Deux études sont présentées pour illustrer le propos, ayant eu pour objet d’estimer, par l’analyse des variations du taux d’avortements précoces, l’impact de l’épizootie de fièvre catarrhale ovine due au sérotype 8 (FCO-8), qui a émergé en France en 2006, puis s’est diffusée dans une large partie du territoire métropolitain en 2007 et 2008. La première étude souligne qu’une analyse des variations temporelles du taux d’avortements précoces à l’échelle du département a permis d’identifier a posteriori l’impact de la FCO-8 sur la survenue d’avortements en élevages de bovins. La seconde étude indique qu’une analyse prospective hebdomadaire des variations temporelles du taux d’avortements précoces aurait permis d’identifier l’impact de la FCO-8 dans un département dans un délai médian de 12 semaines suivant son introduction. Considérant ces résultats, il apparaît pertinent de réfléchir à la mise en place d’une surveillance intégrée des avortements en élevage de bovins, qui reposerait sur deux volets : la déclaration obligatoire des avortements (sous la forme du dispositif actuel en version révisée) et un outil de surveillance syndromique (qui devrait être mis en place à une échelle infra-départementale, en particulier pour améliorer les délais de détection).

Surveillance et gestion d'une épizootie imprévue - analyse et enseignements

Impact de la FCO-8 sur la mortalité des bovins en France en 2007

International audience; Geographical diffusion of scrapic disease is modelled as the outcome of two processes: intra-herd dynamic and regional spreading of genetic and infectious material between herds. The intra-herd dynamic of the disease is represented in this paper by an analytical iterative model with three state variables: the percentage of infected animals, the percentage of resistance alleles, and the percentage of hypersusceptibility alleles. Parameters of this analytical representation are estimated and validated using an existing intra-herd model. The main between-herd contamination path is known to be the trading of animals. Herds contacts on grazing grounds are also suspected to allow disease transmission. Exposure of herds to these contamination paths varies depending on local pastoral habits. We model these contamination paths as diffusion processes in three 1-D spaces: the first represents the situation in winter, where herds are stationed in farms, but when commercial exchanges are also active; the second represents the summer condition for sedentary herds, which are grazing in the vicinity of their farms, but are in contact with other neighbouring herds, and the third represents herds migrating in summer which are strongly exposed to other herds in mountain grazing grounds. We thus obtain a model for the disease diffusion at a regional scale. Using this model it is possible to analyse the influence of different pastoral habits and control measures on the geographic spread of the disease. Furthermore, using both the herd-level model and the regional-level model, we can test the consequences of individual-level hypotheses on regional-level dynamics; this is possible because of the hierarchical transfer of the herd model to the regional disease spread, and because both models are mechanistic.

National audience

International audience; The French Small Ruminant Scrapie Surveillance Scheme has been operating since scrapie became a notifiable disease in France on 14 June 1996. By 1 April 1999, suspicion of scrapie had been reported in 209 sheep flocks and 7 goat flocks, and histopathological diagnosis had been confirmed in 164 sheep flocks and 2 goat flocks. Scrapie was suspected in 37 counties and outbreaks occurred in 24 counties, one of them having 70% of the outbreaks. 66 outbreaks were identified in 1997 and 44 were identified in 1998. The cumulated incidence rate of sheep scrapie was significantly higher in 6 of the 23 counties in which scrapie was identified, compared with the national cumulated incidence rate (1.7/1000 flocks)

International audience

International audience

International audience

International audience