Background

Cattle with L-type (L-BSE) and H-type (H-BSE) atypical Bovine Spongiform encephalopathy (BSE) were identified in 2003 in Italy and France respectively before being identified in other countries worldwide. As of December 2011, around 60 atypical BSE cases have currently been reported in 13 countries, with over one third in France. While the epidemiology of classical BSE (C-BSE) has been widely described, atypical BSEs are still poorly documented, but appear to differ from C-BSE. We analysed the epidemiological characteristics of the 12 cases of L-BSE and 11 cases of H-BSE detected in France from January 2001 to late 2009 and looked for individual risk factors. As L-BSE cases did not appear to be homogeneously distributed throughout the country, two complementary methods were used: spatial analysis and regression modelling. L-BSE and H-BSE were studied separately as both the biochemical properties of their pathological prion protein and their features differ in animal models.

Results

The median age at detection for L-BSE and H-BSE cases was 12.4 (range 8.4-18.7) and 12.5 (8.3-18.2) years respectively, with no significant difference between the two distributions. However, this median age differed significantly from that of classical BSE (7.0 (range 3.5-15.4) years). A significant geographical cluster was detected for L-BSE. Among animals over eight years of age, we showed that the risk of being detected as a L-BSE case increased with age at death. This was not the case for H-BSE.

Conclusion

To the best of our knowledge this is the first study to describe the epidemiology of the two types of atypical BSE. The geographical cluster detected for L-BSE could be partly due to the age structure of the background-tested bovine population. Our regression analyses, which adjusted for the effect of age and birth cohort showed an age effect for L-BSE and the descriptive analysis showed a particular age structure in the area where the cluster was detected. No birth cohort effect was evident. The relatively small number of cases of atypical BSE and the few individual data available for the tested population limited our analysis to the investigation of age and cohort effect only. We conclude that it is essential to maintain BSE surveillance to further elucidate our findings.

Background

The importance of wildlife disease surveillance is increasing, because wild animals are playing a growing role as sources of emerging infectious disease events in humans. Syndromic surveillance methods have been developed as a complement to traditional health data analyses, to allow the early detection of unusual health events. Early detection of these events in wildlife could help to protect the health of domestic animals or humans. This paper aims to define syndromes that could be used for the syndromic surveillance of wildlife health data. Wildlife disease monitoring in France, from 1986 onward, has allowed numerous diagnostic data to be collected from wild animals found dead. The authors wanted to identify distinct pathological profiles from these historical data by a global analysis of the registered necropsy descriptions, and discuss how these profiles can be used to define syndromes. In view of the multiplicity and heterogeneity of the available information, the authors suggest constructing syndromic classes by a multivariate statistical analysis and classification procedure grouping cases that share similar pathological characteristics.

Results

A three-step procedure was applied: first, a multiple correspondence analysis was performed on necropsy data to reduce them to their principal components. Then hierarchical ascendant clustering was used to partition the data. Finally the k-means algorithm was applied to strengthen the partitioning. Nine clusters were identified: three were species- and disease-specific, three were suggestive of specific pathological conditions but not species-specific, two covered a broader pathological condition and one was miscellaneous. The clusters reflected the most distinct and most frequent disease entities on which the surveillance network focused. They could be used to define distinct syndromes characterised by specific post-mortem findings.

Conclusions

The chosen statistical clustering method was found to be a useful tool to retrospectively group cases from our database into distinct and meaningful pathological entities. Syndrome definition from post-mortem findings is potentially useful for early outbreak detection because it uses the earliest available information on disease in wildlife. Furthermore, the proposed typology allows each case to be attributed to a syndrome, thus enabling the exhaustive surveillance of health events through time series analyses.

Background

Ruminant mycoplasmoses are important diseases worldwide and several are listed by the World Organization for Animal Health to be of major economic significance. In France the distribution of mycoplasmal species isolated from clinical samples collected from diseased animals upon veterinary request, is monitored by a network known as VIGIMYC (for VIGIlance to MYCoplasmoses of ruminants). The veterinary diagnostic laboratories collaborating with VIGIMYC are responsible for isolating the mycoplasmas while identification of the isolates is centralized by the French Food Safety Agency (AFSSA) in Lyon. The VIGIMYC framework can also be used for specific surveys and one example, on the prevalence of M. bovis in bovine respiratory diseases, is presented here.

Results

Between 2003 and 2008, 34 laboratories were involved in the network and 1904 mycoplasma isolates, originating from the main ruminant-breeding areas, were identified. For cattle, the high prevalence of M. bovis in bronchopneumonia, notably in young animals, was confirmed by VIGIMYC and an associated specific survey, whereas the non-emergence of species such as M. alkalescens and M. canis was also demonstrated. The etiological agent of bovine contagious pleuropneumonia was never isolated. The principal mycoplasmosis in goats was contagious agalactia with M. mycoides subsp. capri as main agent. Ovine mycoplasmoses, most of which were associated with pneumonia in lambs, were infrequently reported. One exception was ovine contagious agalactia (due to M. agalactiae) that has recently re-emerged in the Pyrénées where it had been endemic for years and was also reported in Corsica, which was previously considered free.

Conclusions

Although VIGIMYC is a passive network and somewhat biased as regards sample collection and processing, it has provided, in this study, an overview of the main mycoplasmoses of ruminants in France. The French epidemiological situation is compared to those existing elsewhere in the world.

Background

During the last decade, active surveillance for transmissible spongiform encephalopathies in small ruminants has been intensive in Europe. In many countries this has led to the detection of cases of atypical scrapie which, unlike classical scrapie, might not be contagious. EU legislation requires, that following detection of a scrapie case, control measures including further testing take place in affected flocks, including the culling of genotype susceptible to classical scrapie. This might result in the detection of additional cases. The aim of this study was to investigate the occurrence of additional cases in flocks affected by atypical scrapie using surveillance data collected in Europe in order to ascertain whether atypical scrapie, is contagious.

Results

Questionnaires were used to collect, at national level, the results of active surveillance and testing associated with flock outbreaks in 12 European countries. The mean prevalence of atypical scrapie was 5.5 (5.0-6.0) cases per ten thousand in abattoir surveillance and 8.1 (7.3-9.0) cases per ten thousand in fallen stock. By using meta-analysis, on 11 out of the 12 countries, we found that the probability of detecting additional cases of atypical scrapie in positive flocks was similar to the probability observed in animals slaughtered for human consumption (odds ratio, OR = 1.07, CI95%: 0.70-1.63) or among fallen stock (OR = 0.78, CI95%: 0.51-1.2). In contrast, when comparing the two scrapie types, the probability of detecting additional cases in classical scrapie positive flocks was significantly higher than the probability of detecting additional cases in atypical scrapie positive flocks (OR = 32.4, CI95%: 20.7-50.7).

Conclusions

These results suggest that atypical scrapie is not contagious or has a very low transmissibility under natural conditions compared with classical scrapie. Furthermore this study stressed the importance of standardised data collection to make good use of the analyses undertaken by European countries in their efforts to control atypical and classical scrapie.

Background

The public health threat represented by a potential circulation of bovine spongiform encephalopathy agent in sheep population has led European animal health authorities to launch large screening and genetic selection programmes. If demonstrated, such a circulation would have dramatic economic consequences for sheep breeding sector. In this context, it is important to evaluate the feasibility of qualification procedures that would allow sheep breeders demonstrating their flock is free from scrapie. Classical approaches, based on surveys designed to detect disease presence, do not account for scrapie specificities: the genetic variations of susceptibility and the absence of live diagnostic test routinely available. Adapting these approaches leads to a paradoxical situation in which a greater amount of testing is needed to substantiate disease freedom in genetically resistant flocks than in susceptible flocks, whereas probability of disease freedom is a priori higher in the former than in the latter. The goal of this study was to propose, evaluate and compare several qualification strategies for demonstrating a flock is free from scrapie.

Results

A probabilistic framework was defined that accounts for scrapie specificities and allows solving the preceding paradox. Six qualification strategies were defined that combine genotyping data, diagnostic tests results and flock pedigree. These were compared in two types of simulated flocks: resistant and susceptible flocks. Two strategies allowed demonstrating disease freedom in several years, for the majority of simulated flocks: a strategy in which all the flock animals are genotyped, and a strategy in which only founders animals are genotyped, the flock pedigree being known. In both cases, diagnostic tests are performed on culled animals. The less costly strategy varied according to the genetic context (resistant or susceptible) and to the relative costs of a genotyping exam and of a diagnostic test.

Conclusion

This work demonstrates that combining data sources allows substantiating a flock is free from scrapie within a reasonable time frame. Qualification schemes could thus be a useful tool for voluntary or mandatory scrapie control programmes. However, there is no general strategy that would always minimize the costs and choice of the strategy should be adapted to local genetic conditions.

Background

The development of active surveillance programmes for transmissible spongiform encephalopathies of small ruminants across Europe has led to the recent identification of a previously undetected form of ovine prion disease, 'atypical' scrapie. Knowledge of the epidemiology of this disease is still limited, as is whether it represents a risk for animal and/or public health.

The detection of atypical scrapie has been related to the use of only some of the EU agreed rapid tests. Information about the rapid tests used is not, as yet, available from public reports on the surveillance of transmissible spongiform encephalopathies in small ruminants. We collected detailed results of active surveillance from European countries to estimate and to compare the prevalence of atypical scrapie and classical scrapie in sheep for each country stratified by each surveillance stream; healthy slaughtered and found dead adult sheep.

Results

From the 20 participating countries, it appeared that atypical scrapie was detected in Europe wherever the conditions necessary for its diagnosis were present. In most countries, atypical scrapie and classical scrapie occurred at low prevalence level. The classical scrapie prevalence estimates were more variable than those for atypical scrapie, which appeared remarkably homogeneous across countries, surveillance streams and calendar years of surveillance. Differences were observed in the age and genotype of atypical scrapie and classical scrapie cases that are consistent with previous published findings.

Conclusion

This work suggests that atypical scrapie is not rare compared to classical scrapie. The homogeneity of its prevalence, whatever the country, stream of surveillance or year of detection, contrasts with the epidemiological pattern of classical scrapie. This suggests that the aetiology of atypical scrapie differs from that of classical scrapie.