A spatio-temporal analysis of BSE cases born before and after the reinforced feed ban in France

A spatio-temporal analysis was carried out to see how the risk distribution of bovine spongiform encephalopathy (BSE) in France changed depending on the period of birth. The data concerned the 539 BSE cases born in France after the ban (BAB) of meat and bone meal (MBM) in 1990 and detected between July 1, 2001 and December 31, 2003, when the surveillance of BSE was comprehensive. Seventy-two of these cases were born after the reinforced (second) ban (BASB) in 1996, which involved the removal of BSE-risk materials and cadavers from the processing of MBM. The Ederer-Myers-Mantel (EMM) time and space cluster test was applied, after classifying the cases by trimester and region of birth, BAB or BASB status, and dairy or beef status. Then disease mapping was performed for four successive birth periods, three for the BAB cases (January 1991 through June 1994, July 1994 through June 1995, July 1995 through June 1996), and one for the BASB (July 1996 through October 1998). It was elaborated with the Bayesian graphical modelling methods and based on a Poisson distribution with spatial smoothing. The parameters were estimated by a Markov Chain Monte Carlo (MCMC) simulation method. The main finding was that the areas with the highest risk of BSE changed largely from one birth period to another; from the west, it reached the east of France for birth cohort 1994-1995 and the southwest for birth cohort 1995-1996. The EMM test identified a peak risk in this region both for dairy and beef cattle in the fall 1995. The spatial distribution of the risk for the BASB cases matched the spatial pattern of risk for the preceding BAB birth cohort quite well; this was in favour of a common origin of the infection of the BAB and BASB cases, despite the complementary control measures.     

Geographical clustering of cases of bovine spongiform encephalopathy (BSE) born in Switzerland after the feed ban

Over one-third of the cases of BSE in Switzerland have been born after the feed ban of December 1, 1990. Evidence for the geographical clustering of these cases emerged in two distinct regions. All the 354 BSE cases recorded until June 30, 2000 (set A), and the 376 cases recorded up to May 14, 2001 (set B), were georeferenced to the centres of the communities in which the herds of origin were located, and control populations were georeferenced to the centres of the communities in which these herds were located at the time of the census. The latitudes and longitudes of these centres were used in the statistical analysis of the spatial clustering. The Cuzick-Edwards test and the spatial scan statistics were applied to assess the significance of the clusters, while controlling for the spatial distribution of the underlying cattle population. There was global clustering of the cases born after the ban, and distinct and significant (P<0.05) spatial clusters were repeatedly identified in the two case datasets, and in several control populations (all cases born before the feed ban on a random sample of control farms) in terms of cattle density by region or cow density by region. Differential reporting was excluded as the underlying reason for the observed clusters.     

Spatial heterogeneity of the risk of BSE in France following the ban of meat and bone meal in cattle feed

In France, meat-and-bone meal (MBM) has been prohibited for cattle feeding since 1990, but bovine spongiform encephalopathy (BSE) cases, called 'NAIF', appeared in animals born after this feed ban. Furthermore, in 1996 a new measure was taken: removal of cadavers and specified risk materials (SRM) from the processing of MBM dedicated to animal feed. Nevertheless, BSE cases (called 'super-NAIF') appeared in cattle born after this measure was in force. We analysed the spatial distribution of 445 'NAIF' and 58 'super-NAIF' cases detected in France from July 1, 2001 to July 31, 2003. The detection of BSE was based both on the mandatory reporting system (MRS) and the systematic test screening of cattle at the abattoir and at the fallen-animal plant with rapid tests. The background population was based on the adult-cow census. The disease mapping of the BSE risk was based on the standardised incidence ratio (stochastic Poisson process). A spatial component, which takes into account the spatial dependence between the geographical units by a notion of adjacency was used to eliminate the over-dispersion in the risk assessment. The geographical units were defined by hexagons with a side of 23km (France had 1264 hexagons). The parameters were estimated by a Metropolis Gibbs sampling algorithm using the Markov-chain Monte Carlo methods. The BSE cases were not randomly distributed. Furthermore, the areas at risk for the 'super-NAIF' matched part of the areas at risk for the 'NAIF' cases-which suggests that it might be a common source of contamination.     

Poultry, pig and the risk of BSE following the feed ban in France--a spatial analysis

A spatial analysis was carried out in order to analyse the reason why the risk of Bovine Spongiform Encephalopathy (BSE) was spatially heterogeneous in France, during the period following the feed ban of Meat and Bone Meal to cattle. The hypothesis of cross-contamination between cattle feedstuff and monogastric feedstuff, which was strongly suggested from previous investigations, was assessed, with the assumption that the higher the pig or poultry density is in a given area, the higher the risk of cross-contamination and cattle infection might be. The data concerned the 467 BSE cases born in France after the ban of meat and bone meal (July 1990) and detected between July 1st, 2001 and December 31, 2003, when the surveillance system was optimal and not spatially biased. The disease mapping models were elaborated with the Bayesian graphical modelling methods and based on a Poisson distribution with spatial smoothing (hierarchical approach) and covariates. The parameters were estimated by a Markov Chain Monte Carlo simulation method. The main result was that the poultry density did not significantly influence the risk of BSE whereas the pig density was significantly associated with an increase in the risk of 2.4% per 10 000 pigs. The areas with a significant pig effect were located in regions with a high pig density as well as a high ratio of pigs to cattle. Despite the absence of a global effect of poultry density on the BSE risk, some areas had a significant poultry effect and the risk was better explained in some others when considering both pig and poultry densities. These findings were in agreement with the hypothesis of cross-contamination, which could take place at the feedstuff factory, during the shipment of food or on the farm. Further studies are needed to more precisely explore how the cross-contamination happened.     

Area-level risks for BSE in British cattle before and after the July 1988 meat and bone meal feed ban

In this paper we investigate area-level risk factors for BSE for the cattle population present in Great Britain between 1986 and 1997. By dividing this population into two birth cohorts, those born before the July 1988 ban on feeding ruminant-derived meat and bone meal to ruminants and those born after, second-order regional influences are distinguished from the strong first-order south-to-north gradient of area-level BSE risk using Bayesian hierarchical models that account for structured (spatially correlated) and unstructured heterogeneity in the data. For both cohorts area-level risk of BSE was increased by a more southerly location and greater numbers of dairy cattle, relative to non-dairy cattle. For the cohort of cattle born after the July 1988 ban on feeding ruminant-derived meat and bone meal area-level BSE risk was additionally associated with greater numbers of pigs, relative to cattle. These findings support the role of low level cross-contamination of cattle feed by pig feed as an influence on BSE incidence risk as the epidemic evolved. Prior to the 1988 meat and bone meal ban unexplained BSE risk was relatively uniformly distributed across the country whereas after the ban there were spatially aggregated areas of unexplained risk in the northern and eastern regions of England suggesting that local influences allowed BSE control measures to be less-successfully applied in these areas, compared with the rest of the country. We conclude that spatially localised influences were operating in divergent ways during the two phases of the epidemic.     

Cases of bovine spongiform encephalopathy born in Switzerland before and after the ban on the use of bovine specified risk material in feed

In Switzerland there was a reduction in the number of cases of bovine spongiform encephalopathy, observed in the birth cohorts from 1995 to 1996, but no further reduction in the following birth cohorts up to 1998. From the records of 34 cases born after April 30, 1996 (BAB96) and 174 cases born before April 30, 1996 and after December 1990 (BAB90), observed up to April 30, 2004, the risk factors at the farm level, possible routes of exposure and the geographical distribution of the cases were analysed to try to explain the observations. No evidence was found for a rate of exposure other than feed. There was some evidence that the risk factors at farm level were different between the BAB90 and BAB96 cases. A large proportion of the BAB96 cases was born in cantons that had reported only a few BAB90 cases, but a small cluster of the BAB96 cases was found in a region where there had been a cluster of BAB90 cases. The spatial distribution of these cases indicated that the risk of exposure to infection had been more randomly distributed than during the period up to April 1996. Farms with mixed livestock had a higher risk of having a case born after the ban on the feeding of specified risk material in 1996. In a regression model, a trend towards an association between cases of BSE and presence of small ruminants on the farm was observed for the BAB96 cases, and the presence of pigs and the pig:cattle ratio were significant for the BAB90 cases.     

Cross-contamination of ruminant feed stuffs in Bavaria after the comprehensive feed ban

The results of the official feed control program in Bavaria between 1997 and 2002 document that the proportion of ruminant feedstuffs that was cross-contaminated with animal material was distinctively reduced after the comprehensive feed ban since 2001, and decreased close to zero in 2002. The results underline the high efficiency of the comprehensive feed ban. They also indicate risks of a potential re-admittance of animal protein for nonruminant domestics under the momentary production procedures.     

Case-control study of cases of bovine spongiform encephalopathy born after July 31, 1996 (BARB cases) in Great Britain

This paper reports the results of a case-control study of the bovine spongiform encephalopathy (BSE) cases born in Great Britain after the statutory reinforcement of the ban (BARB) on the feeding of mammalian-derived meat and bone meal on 31 July 1996. A total of 499 suspect clinical cases of BSE, born after 31 July 1996, and reported negative by July 31, 1996 and were compared with the set of 164 confirmed Great BARB cases in Great Britain detected by both passive and active surveillance. Animal-level risk factors (age and type of feed offered) and herd-level risk factors (herd size and type, number of prereinforced feed ban BSE cases born on the holding, the presence of other domestic species and waste management) were obtained for the analysis. BARB cases were 2.56 times (95 per cent CI 1.29 to 5.07) more likely to be exposed to homemix or a combination of homemix and proprietary feeds were 0.59 times (95 per cent CI 0.50 to 0.69) as less likely to be exposed to the unit increases in the number of prereinforced feed ban BSE cases diagnosed on the natal holding. A supplementary spatial analysis of these cases revealed three areas of excess BARB density: Northwest and Southwest of Wales and Northeast of Scotland.     

Animal feeding and feed legislation after the detection of the first indigenous BSE cases in Germany

In Great Britain, even the earliest tangible signs indicating the epidemiologic significance of meat and bone meal in the spreading of BSE soon gave rise to increasingly rigorous legislative measures regulating animal feedstuffs. In 1994 a ban on the feeding of animal proteins to ruminants was implemented throughout the entire EU. But until the first BSE cases were actually confirmed in locally raised cattle (November 2000), feeding practice and legislation more or less in Germany remained unaffected by the efforts undertaken in Great Britain. This situation was suddenly changed on 1 December, 2000, when the so-called "Verfütterungsverbot" was put into effect, a law which drastically extended bans regarding the feedstuffs (including fishmeal and animal fats) as well as the species concerned (all animals used in food production). In 2001 the "contamination" phenomenon (ingredients of animal origin were detected in mixed feeds) became a vital issue for the feed industry; through the media, the subject "feedstuff safety" gained a previously unseen level of public awareness. Those circles concerned with mixed feed production and animal husbandry were increasingly confronted with the consequences of the "Verfütterungsverbot" (availability and pricing of substitute ingredients; the demand for amino acids and inorganic sources of phosphorus; problems finding adequate substitutes for animal fats; poor digestibility of alternative components such as indigenous legumes or vegetable fats in calf diets; lower utilization rate of original phosphorus in mixed feeds with negative consequences for skeletal development). With the conditional approval of fishmeal (except in feeds for ruminants) the situation has eased again to a certain degree; on the EU level there are increasing signals pointing toward a political intention to reinstate the utilization of by-products of slaughtered animals qualified for human consumption (with the exception of fallen/dead animals and specific risk material) in poultry and swine feeding. In Germany, at least, the question of animal fat utilization for food-producing animals is still unsolved.     

Targeted surveillance to assess the prevalence of BSE in high-risk populations in western France and the associated risk factors

A pilot study was set up for the first time in France in August 2000, to obtain more precise estimates on the BSE epidemic in France. Three categories of cattle at risk of BSE (found dead on-farm, euthanased and emergency slaughtered) were sampled exhaustively from August 7 to December 22, 2000, in the three regions assumed to be the most affected with BSE in France (Basse-Normandie, Bretagne and Pays de la Loire). The samples were checked by using Prionics tests, and positive samples were confirmed by Western blot or immunohistochemistry. The overall prevalence of positive cattle was 0.16 per cent. Multifactorial logistic regression showed that there was a significantly higher prevalence among cattle from the birth cohorts July 1993 to June 1994 and July 1994 to June 1995, than among those born before July 1993, and among the categories 'euthanased' and 'emergency slaughtered' than among the category 'dead on-farm, and a higher prevalence in the regions Pays de la Loire and Bretagne than in Basse-Normandie. No significant differences in the prevalence of BSE were observed between dairy, beef suckler and mixed herds.     

Questionnaire analysis of BSE cases in France detected by active surveillance and the reasons for non-notification

A mandatory reporting system (MRS) was set up in France in December 1990 to detect animals showing clinical signs of bovine spongiform encephalopathy (BSE). Since June 2000, four active surveillance programmes dedicated to fallen stock and slaughtered cattle have been implemented to reinforce the MRS. The clinical status of the cases detected through these programmes was investigated to understand why the MRS had failed to detect them. Up to September 1, 2002, 181 cases had been analysed (126 fallen stock and 55 slaughtered cattle). Almost all the fallen stock cases were animals which had been showing clinical signs, and two thirds of them had shown signs which should have led to a suspicion of BSE. No clinical signs had been reported for two thirds of the slaughtered cattle cases and 10 (8 per cent) of the fallen stock cases.     

Case-control study to investigate risk factors for horse falls in hurdle racing in England and Wales

Between March 1, 2000 and August 31, 2001, a case-control study was conducted on 12 racecourses in England and Wales to identify and quantify the risk factors associated with horse falls in hurdle races. The cases and controls were defined so that variables relating to the horse, the jockey, the race and racecourse, and the jump could be considered. The cases were defined as a jumping effort at a hurdle flight that resulted in a fall, and the controls were defined as a successful jump over a hurdle at any of the 12 racecourses within 14 days before or after the case fall. Conditional logistic regression was used to examine the univariable and multivariable relationships between the predictor variables and the risk of falling. The risk of falling was significantly associated with the position of the jump in the race, and with the distance and speed of the race. A horse's previous racing experience and history were also significantly associated with the risk of falling and horses participating in their first hurdle race were at almost five times greater risk of falling than horses that had hurdled before.     

Case-control study of risk factors associated with nosocomial Salmonella krefeld infection in dogs

In a case-control study of risk factors associated with an episode of nosocomial Salmonella krefeld infection in dogs at the veterinary medical teaching hospital, data on 20 case dogs and 75 control dogs were obtained by review of hospital records. Univariate and multivariate statistical analyses were carried out for possible risk factors for infection to obtain odds of Salmonella krefeld isolation, given exposure to each risk factor of interest. Compared with control dogs, case dogs were 11.9 times more likely to have been fed rice, 7 times more likely to have had radiography done, 10.2 times more likely to have been a resident in ward 2, 5.6 times more likely to have been given antimicrobial agents orally, 11.3 times more likely to have been given antimicrobial agents parenterally, and 37.9 times more likely to have been given antimicrobial agents orally and parenterally (P less than 0.05).