Prevalence of classical swine fever, Aujeszky's disease and brucellosis in a population of wild boar in Switzerland.

During two survey rounds of a national surveillance system for infectious diseases in wild boar in Switzerland, each lasting four months from November to February, between 2001 and 2003, 1949 blood samples and 62 tissue samples from the spleen and 50 from the reproductive organs were collected from hunted wild boar. The survey was designed so that freedom from infection could be detected with a probability of 95 per cent at a threshold prevalence of less than 1 per cent for classical swine fever and Aujeszky's disease and less than 1.5 per cent for brucellosis. There was no serological evidence of classical swine fever or Aujeszky's disease, but brucellosis due to Brucella suis biovar 2 was confirmed serologically and by bacterial isolation.

Genetic heterogeneity of pestiviruses of ruminants in Switzerland.

We have genetically analyzed ruminant pestiviruses. All >150 bovine viral diarrhea (BVD) viruses isolated from cattle in Switzerland belonged to genotype 1, with subgenogroups e, h, k and b found in decreasing frequency. To date, representatives of subgenogroup k have been detected in Switzerland only. Despite serological evidence of Border disease in sheep, only few Border disease viruses have been isolated, all of which belong to the novel group 3. Serological evidence suggested that pestivirus infections may occur also in wild ruminants in Switzerland but no isolates are available for analysis. In addition, we describe two pestiviruses, one a cell culture contaminant and the other isolated from a buffalo, that cluster with a recently proposed novel pestivirus species.

Risk factors for the infection of Swiss goat herds with small ruminant lentivirus: a case-control study.

In the mid-1980s, Switzerland started a programme to eradicate caprine arthritis-encephalitis - an infectious disease of goats caused by the small ruminant lentivirus (srlv). Since 1996, progress towards eradication has slowed down, owing to infections occurring on farms from which the infection had previously been eliminated. To investigate specific risk factors for these new infections and to improve the eradication programme, a case-control study was conducted. Cases consisted of farms that had been officially free of srlv for at least three consecutive years but on which at least one srlv-seropositive animal had been detected during the annual serological surveys of 2001 and 2002. On all the case and control farms where sheep were housed together with goats, a subset of sheep was screened for antibodies to srlv. Potential risk factors were analysed in a logistic regression model; the results indicated that close contact with srlv-seropositive sheep was highly correlated with seroconversion in srlv-seronegative goat herds (odds ratio=26.9), supporting the hypothesis that srlv can be transmitted between sheep and goats, and suggesting that the measures taken so far will not lead to the complete eradication of srlv from Switzerland within the next few years.

Estimating the probability and level of contamination with Salmonella of feed for finishing pigs produced in Switzerland--the impact of the production pathway.

Contaminated feed is a source of infection with Salmonella for livestock, including pigs. Because pigs rarely show clinical signs of salmonellosis, undetected carriers can enter the food production chain. In a "Farm to Fork" food safety concept, safe feed is the first step for ensuring safe food. Heat treatment or adding organic acids are process steps for reducing or eliminating a contamination with Salmonella. The aims of this study were (I) to estimate the probability and the level of Salmonella contamination in batches of feed for finishing pigs in Swiss mills and (II) to assess the efficacy of specific process steps for reducing the level of contamination with Salmonella. A quantitative release assessment was performed by gathering and combining data on the various parameters having an influence on the final contamination of feed. Fixed values and probability distributions attributed to these parameters were used as input values for a Monte Carlo simulation. The simulation showed that-depending on the production pathway-the probability that a batch of feed for finishing pigs contains Salmonella ranged from 34% (for feed on which no specific decontaminating step was applied) to 0% (for feed in which organic acids were added and a heat treatment was implemented). If contamination occurred, the level of contamination ranged from a few Salmonella kg(-1) feed to a maximum of 8E+04 Salmonella kg(-1) feed. Probability and levels of contamination were highest when no production process able to reduce or eliminate the pathogen was implemented. However, most of the Swiss production was shown to undergo some kind of decontaminating step. A heat treatment, in combination with the use of organic acids, was found as a solution of choice for the control of Salmonella in feed.

[Enzootic pneumonia (EP) in Swiss swine herds after area-wide eradication: epidemiological analysis of outbreaks occurring between 1999 and 2003]. / Enzootische Pneumonie (EP) in schweizerischen Schweinebeständen nach Abschluss der flächendeckenden Sanierung: Epidemiologische Analyse 1999-2003.

In a retrospective analysis, infections of swine herds with Enzootic Pneumonia (EP), occurring after the regional eradication programme had been completed, were evaluated and described according to epidemiological criteria. The aim of this study was to obtain interim results about status, progress and trends of the area-wide eradication in Switzerland over all regions involved in the programme. The population comprised pig farms with eradication of EP completed by the end of 2002. Incidence of EP infection was calculated for the years 2000-2003. Seasonal effects, influences from production-type, herd size, and pig density in the surrounding area on incidences of EP outbreaks were investigated. In 2000-2002, annual incidences were steadily decreasing from 3.1% to 2.0%, and they showed great regional variation. In 2003, contrary to the long-term trend, a minor increase of overall incidence from 2.0% to 2.1% was observed while the incidence for breeding-only farms continued to recede. Possible explanations for this are discussed. Previous observations on EP infections accumulating in the cold season could not be confirmed. Large farms, finishing farms, and farms located in densely populated pig areas as well as farms being part of multisite production rings had a higher risk of infection. In spite of occurrence of EP outbreaks in eradicated areas, the current status of the area-wide eradication is promising, and a further decline in incidence of EP infection can be expected in the future.

[Demographic characteristics of dog population in Switzerland]. / Demographie der Hundepopulation in der Schweiz.

Dog Registration data from three Cantons, patient data of 13 veterinary practices and registrations in the Swiss Dog Pedigree Book were collected, analysed and compared to results of a commercial household survey, to assess demographic characteristics of dog population in Switzerland. The proportion of "pure-bred" dogs was different depending on how the term was used, varying from 24% regarding registrations in the Swiss Dog Pedigree Book, to 75% regarding dogs with only one breed recorded in Veterinarian's patient-history-management systems. Most popular breeds were dogs called "German Shepherd/Shepherd", followed by the Labrador and Golden Retriever. Comparison of different data sources suggested regional differences in popularity of breeds. The average life expectancy was estimated on 10.5 and 11 years. Sex distribution was equal. One third of all male dogs and half of the female dogs were neutered. Regardless sex, neutering was more common in cross-bred dogs than in "pure-bred" dogs (OR = 1.9). Some bias in all sources had to be considered and there was a major concern regarding definition of breeds. However, the study was able to add different parameters out of different sources to a homogenous picture of demographic data of dog population in Switzerland.

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.

[A method to identify BSE suspects in emergency slaughtered cattle during ante mortem examination]. / Eine Methode zur Erkennung von BSE-Verdachtsfällen in der Gruppe der krankgeschlachteten Rinder während der ante mortem Untersuchung.

A method is presented by which a maximal number of BSE-infected cattle that had escaped the filter of clinical examination are identified during ante mortem examination. This approach might prove to be an efficient and cost-effective method for veterinary and non-veterinary meat inspectors to remove infected animals prior to slaughter. In a case-control study, the clinical signs of 224 randomly selected sick slaughtered animals were compared with the clinical signs of 26 sick slaughtered animals in which BSE infection was diagnosed using a rapid test post mortem. In addition, the clinical signs of the sick slaughtered BSE-positive animals were compared with the clinical signs of a group of BSE suspects identified during the same time period and in which BSE infection could be confirmed. As a result of this study a mathematical model was developed to identify BSE suspects. This model contains a total of 7 variables (clinical signs) that proved to be of importance. These signs were aggressive behaviour, grinding of teeth, protruding eyeballs, reduced rumination, inability to stand, overexcitability, and difficulty in standing up. The presented model has a sensitivity of 61.5% (16 out of 26 BSE-positive animals slaughtered while sick were identified) and a specificity of 99.6% when compared to a rapid test conducted post mortem.

[Geographic distribution of BSE in Switzerland]. / Räumliche Verteilung der BSE in der Schweiz.

Visual evaluation of the occurrence of BAB (born after ban) cases pointed towards spatial clustering. Therefore a statistical analysis of spatial case clustering was conducted using GIS technology. In the initial analysis, all 376 cases (135 BAB, 241 BBB/born before ban) diagnosed through mid of March 2001 were investigated using the spatial scan statistic. Two clusters of BBB cases were identified in the western part of Switzerland, and two clusters of BAB cases in the eastern part. Epidemiological investigations performed within the BAB clusters showed an increased pig density in these cluster regions. Pig density is considered an indicator for the probability of contamination of cattle feed with feed containing meat-and-bone meal that is intended for other species (cross-contamination). In an updated cluster analysis including all cases reported until end of June 2002 (data set B), clusters were identified in the same regions as previously. It was shown that the BAB clusters occurred in different time periods. The small scale differences in cluster size and location are discussed, with an emphasis on the implications for following epidemiological investigations.

The effect of infection with bovine viral diarrhea virus on the fertility of Swiss dairy cattle.

Bovine viral diarrhea virus is a major cattle pathogen with a worldwide distribution. Animals may be infected with BVD virus transiently or persistently. Transient infection leads to protective immunity. Persistent infection is unique because it is associated with an immunotolerance that is specific to the infecting strain of BVD virus. Persistent infection results from viral invasion of fetuses between the second and fourth month of development. Such animals are of prime importance in the epidemiology of BVD because they shed large amounts of virus, and thus serve as a constant source of infection for non-immune animals. Infection of pregnant animals during the first two months of gestation may result in an increased rate of return to estrus. Animals infected in the period of five months to birth may abort or give birth to calves with malformations. The effects of BVD virus on fertility and gestation are well documented from experimental infection. However, much less is known of the extent of losses under field conditions. The main reason for this may be the multitude of other causes of increased return rates and gestation failures. In addition, the incidence of infection with BVD virus may vary over time and depends on management practices. In this study, we investigated the impact of BVD virus on gestation failures under field conditions in a large cattle-breeding area of Switzerland, where no specific measures to control BVD are in effect. Our approach consisted of relating seroconversions to BVD virus with the rate of return to estrus, abortion, and birth of calves with apparent malformations. These parameters of fertility were compared to those of animals immune to BVDV infection due to previous exposure to the virus and animals without seroconversion. Our data show that infection with BVD virus during the first 45 days of gestation did not influence the rate of return to estrus. By contrast, we observed a statistically significant increase in the abortion rate in mid-term gestation (Days 46 to 210) while no such effect was observed in the later stages of gestation. No clinically manifest malformations were observed in the offspring of animals that had seroconverted to BVD virus. In our study population the prevalence of BVDV antibody positive cattle varied only slightly between 78% and 80% over the period of observation. Our data showed that 7% (CI: 2.4-14%) of fetal deaths may be attributable to infection with BVD virus.

Prevalence of cattle infected with bovine viral diarrhoea virus in Switzerland.

A cross-sectional study was made in a major cattle-breeding area of Switzerland to investigate the prevalence and local distribution of animals antibody positive to bovine viral diarrhoea (BVD) virus and of persistently infected animals. The sample size and statistical analysis took into account the possible clustering of persistently infected animals on individual farms. Of 3440 animals tested on 121 farms, 1982 were found to have antibodies to BVD virus (95 per cent confidence interval for the population prevalence: 57.6+/-4.5 per cent) and 22 were persistently infected (estimate for the population prevalence: 0.64+/-0.34 per cent). The detection of persistent infection in animals less than seven months old was improved either by retesting one year later, by using an antigen-capture ELISA or, in selected cases, by the analysis of original serum samples by reverse-transcription PCR. The results showed that the prevalence of persistent infection may be underestimated by as much as one-third when antigen detection alone is used. None of the 121 farms investigated was free of antibody-positive animals and one in eight herds had at least one animal that was persistently infected. The prevalence of antibodies was lowest in seven- to 12-month-old animals (22.9 per cent) and highest in animals aged five years or over (84.9 per cent).