Review on the epidemiology and dynamics of BSE epidemics

The paper describes how the comprehensive surveillance of bovine spongiform encephalopathy (BSE) and studies carried out on these data has enhanced our knowledge of the epidemiology of BSE. Around 7 000 BSE cases were detected through the screening of about 50 million cattle with rapid tests in Europe. It confirmed that the clinical surveillance had a poor capacity to detect cases, and also showed the discrepancy of this passive surveillance efficiency between regions and production types (dairy/beef). Other risk factors for BSE were being in a dairy herd (three times more than beef), having a young age at first calving (for dairy cattle), being autumn-born (dairy and beef), and being in a herd with a very high milk yield. These findings focus the risk on the feeding regimen of calves/heifers. Several epidemiological studies across countries suggest that the feedborne source related to meat and bone meal (MBM) is the only substantiated route of infection ¿ even after the feed ban ¿, while it is not possible to exclude maternal transmission or milk replacers as a source of some infections. In most European countries, the average age of the cases is increasing over time and the prevalence decreasing, which reflects the effectiveness of control measures. Consistent results on the trend of the epidemic were obtained using back-calculation modelling, the R0 approach and Age-Period-Cohort models. Furthermore, active surveillance also resulted in the finding of atypical cases. These are distinct from previously found BSE and classified in two different forms based on biochemical characteristics; their prevalence is very low (36 cases up to 1st September 2007), affected animals were old and some of them displayed clinical signs. The origin and possibility of natural transmission is unknown

How the surveillance system may bias the results of analytical epidemiological studies on BSE: prevalence among dairy versus beef suckler cattle breeds in France

Until recently, epidemiological studies on Bovine Spongiform Encephalopathy (BSE) were based on Mandatory Reporting Systems (MRS) of clinically suspect bovines only, but rapid diagnostic tests were validated in 1999 and are used for targeted surveillance in Switzerland, France and other countries, as a complementary and secondary tool. Data on 30491 cattle issued from a French pilot program targeted at cattle having died on the farm, subjected to euthanasia or sent for emergency slaughter, did not show any significant difference in BSE risk between dairy and beef suckler breeds. The data also revealed that part of the clinical cases of BSE escaped the MRS, which permitted to detect more dairy than beef suckler affected cattle compared to the targeted surveillance in the same period (from August to December 2000) and region (Bretagne, Pays de la Loire and Basse Normandie regions). Analyzing together the data of the targeted surveillance and mandatory reporting system programs with a non-conditional logistic regression, we found that the odds of a dead cow being a BSE case among all dead cattle was 3.2 times higher for dairy breeds compared to beef suckler breeds. This confirmed British findings but points out to the fact that considering either MRS or targeted surveillance data alone may possibly create biases in epidemiological studies on BSE

Transmission and characterization of bovine spongiform encephalopathy sources in two ovine transgenic mouse lines (TgOvPrP4 and TgOvPrP59).

International audienc

Spatial and Temporal Epidemiology of Nephropathia Epidemica Incidence and Hantavirus Seroprevalence in Rodent Hosts: Identification of the Main Environmental Factors in Europe

International audienceIn Europe, the increasing number of nephropathia epidemica (NE) infections in humans, caused by Puumala virus carried by bank voles (Myodes glareolus), has triggered studies of environmental factors driving these infections. NE infections have been shown to occur in specific geographical areas characterized by environmental factors that influence the distribution and dynamics of host populations and virus persistence in the soil. Here, we review the influence of environmental conditions (including climate factors, food availability and habitat conditions) with respect to incidence in humans and seroprevalence in rodents, considering both direct and indirect transmission pathways. For each type of environmental factor, results and discrepancies between studies are presented and examined in the light of biological hypotheses. Overall, food availability and temperature appear to be the main drivers of host seroprevalence and NE incidence, but data quality and statistical approaches varied greatly among studies. We highlight the issues that now need to be addressed and suggest improvements for study design in regard to the current knowledge on hantavirus epidemiology

Analyse de la mortalité bovine en France de 2003 à 2009

La mortalité bovine est un problème important, tant au plan économique que du point de vue du bien-être animal. Nous avons analysé les données enregistrées dans la base de données nationale d'identification de 2003 à 2009, décrivant la carrière d'environ 75 millions de bovins, afin de fournir des statistiques fiables de la mortalité bovine en France. Les résultats de cette étude constituent un référentiel pouvant être utilisé pour évaluer des situations observées en élevage. En moyenne sur cette période, le risque de mortalité périnatale des mâles et des femelles atteignait respectivement 7,9% et 6,0% dans le cheptel laitier, et 4,7% et 3,2% dans le cheptel allaitant. Le risque de mortalité annuel moyen des animaux de plus de deux ans était de 3,5% chez les laitiers et de 2,0% chez les allaitants. La mortalité des bovins laitiers était significativement plus élevée que celle des allaitants pour les dix classes d'âge étudiées, sauf celle de un à deux ans. La modélisation des données hebdomadaires a permis de décrire la saisonnalité des taux de mortalité, qui était différente selon le sous-groupe populationnel considéré. Les taux de mortalité des veaux de moins de sept jours présentaient notamment deux pics d'ampleur équivalente (en décembre et juillet), tandis que les autres classes d'âge présentaient un pic principal en hiver, visiblement associé chez les adultes au pic de vêlage. Les résultats de cette modélisation ont par ailleurs révélé une augmentation significative des taux de mortalité de 2003 à 2009, probablement en partie due à l'épizootie de fièvre catarrhale ovine qui s'est propagée en France en 2007-2008. L'augmentation des taux de mortalité bovine a déjà été constatée dans de nombreux pays, suggérant la nécessité de mettre en place des mesures correctrices.Cattle mortality represents both an economical and an animal welfare issue. We analyzed the data recorded in the National Cattle Register from 2003 to 2009, gathering data about 75 million cattle, to provide reliable statistics of cattle mortality in France. On average over this period, the perinatal mortality risk in males and females reached respectively 7.9% and 6.0% in dairy cattle, and 4.7% and 3.2% in beef cattle. The average annual mortality risk of animals over two years was 3.5% for dairy and 2.0% for beef cattle. Mortality of dairy cattle was significantly higher than that of beef cattle for the ten age groups studied, except for those of one to two years. Weekly data were modeled to describe the seasonality of mortality, which was different among the different sub-population groups. The mortality rate of calves less than seven days old showed two peaks of equal magnitude (in December and July), while other age groups showed a major peak in the winter, apparently associated in adults to the peak of calving. The modeling results of the model also revealed a significant increase in death rates from 2003 to 2009, probably partly due to the blue tongue epizootic that spread in France from 2007 to 2008. Rising rates of cattle mortality have already been observed in many countries, suggesting the need to implement corrective measures