Eradication of Bovine Viral Diarrhoea (BVD) in Cattle in Switzerland: Lessons Taught by the Complex Biology of the Virus.

Bovine viral diarrhoea virus (BVDV) and related ruminant pestiviruses occur worldwide and cause considerable economic losses in livestock and severely impair animal welfare. Switzerland started a national mandatory control programme in 2008 aiming to eradicate BVD from the Swiss cattle population. The peculiar biology of pestiviruses with the birth of persistently infected (PI) animals upon in utero infection in addition to transient infection of naïve animals requires vertical and horizontal transmission to be taken into account. Initially, every animal was tested for PI within the first year, followed by testing for the presence of virus in all newborn calves for the next four years. Prevalence of calves being born PI thus diminished substantially from around 1.4% to <0.02%, which enabled broad testing for the virus to be abandoned and switching to economically more favourable serological surveillance with vaccination being prohibited. By the end of 2020, more than 99.5% of all cattle farms in Switzerland were free of BVDV but eliminating the last remaining PI animals turned out to be a tougher nut to crack. In this review, we describe the Swiss BVD eradication scheme and the hurdles that were encountered and still remain during the implementation of the programme. The main challenge is to rapidly identify the source of infection in case of a positive result during antibody surveillance, and to efficiently protect the cattle population from re-infection, particularly in light of the endemic presence of the related pestivirus border disease virus (BDV) in sheep. As a consequence of these measures, complete eradication will (hopefully) soon be achieved, and the final step will then be the continuous documentation of freedom of disease.

Development of Reporting Guidelines for Animal Health Surveillance-AHSURED.

With the current trend in animal health surveillance toward risk-based designs and a gradual transition to output-based standards, greater flexibility in surveillance design is both required and allowed. However, the increase in flexibility requires more transparency regarding surveillance, its activities, design and implementation. Such transparency allows stakeholders, trade partners, decision-makers and risk assessors to accurately interpret the validity of the surveillance outcomes. This paper presents the first version of the Animal Health Surveillance Reporting Guidelines (AHSURED) and the process by which they have been developed. The goal of AHSURED was to produce a set of reporting guidelines that supports communication of surveillance activities in the form of narrative descriptions. Reporting guidelines come from the field of evidence-based medicine and their aim is to improve consistency and quality of information reported in scientific journals. They usually consist of a checklist of items to be reported, a description/definition of each item, and an explanation and elaboration document. Examples of well-reported items are frequently provided. Additionally, it is common to make available a website where the guidelines are documented and maintained. This first version of the AHSURED guidelines consists of a checklist of 40 items organized in 11 sections (i.e., surveillance system building blocks), which is available as a wiki at https://github.com/SVA-SE/AHSURED/wiki. The choice of a wiki format will allow for further inputs from surveillance experts who were not involved in the earlier stages of development. This will promote an up-to-date refined guideline document.

Cost distribution of bluetongue surveillance and vaccination programmes in Austria and Switzerland (2007-2016).

Bluetongue virus (BTV) is an emerging transboundary disease in Europe, which can cause significant production losses among ruminants. The analysis presented here assessed the costs of BTV surveillance and vaccination programmes in Austria and Switzerland between 2007 and 2016. Costs were compared with respect to time, type of programme, geographical area and who was responsible for payment. The total costs of the BTV vaccination and surveillance programmes in Austria amounted to €23.6 million, whereas total costs in Switzerland were €18.3 million. Our analysis demonstrates that the costs differed between years and geographical areas, both within and between the two countries. Average surveillance costs per animal amounted to approximately €3.20 in Austria compared with €1.30 in Switzerland, whereas the average vaccination costs per animal were €6.20 in Austria and €7.40 in Switzerland. The comparability of the surveillance costs is somewhat limited, however, due to differences in each nation's surveillance (and sampling) strategy. Given the importance of the export market for cattle production, investments in such programmes are more justified for Austria than for Switzerland. The aim of the retrospective assessment presented here is to assist veterinary authorities in planning and implementing cost-effective and efficient control strategies for emerging livestock diseases.

Evidence for Emergency Vaccination Having Played a Crucial Role to Control the 1965/66 Foot-and-Mouth Disease Outbreak in Switzerland.

Foot-and-mouth disease (FMD) is a highly contagious disease that caused several large outbreaks in Europe in the last century. The last important outbreak in Switzerland took place in 1965/66 and affected more than 900 premises and more than 50,000 animals were slaughtered. Large-scale emergency vaccination of the cattle and pig population has been applied to control the epidemic. In recent years, many studies have used infectious disease models to assess the impact of different disease control measures, including models developed for diseases exotic for the specific region of interest. Often, the absence of real outbreak data makes a validation of such models impossible. This study aimed to evaluate whether a spatial, stochastic simulation model (the Davis Animal Disease Simulation model) can predict the course of a Swiss FMD epidemic based on the available historic input data on population structure, contact rates, epidemiology of the virus, and quality of the vaccine. In addition, the potential outcome of the 1965/66 FMD epidemic without application of vaccination was investigated. Comparing the model outcomes to reality, only the largest 10% of the simulated outbreaks approximated the number of animals being culled. However, the simulation model highly overestimated the number of culled premises. While the outbreak duration could not be well reproduced by the model compared to the 1965/66 epidemic, it was able to accurately estimate the size of the area infected. Without application of vaccination, the model predicted a much higher mean number of culled animals than with vaccination, demonstrating that vaccination was likely crucial in disease control for the Swiss FMD outbreak in 1965/66. The study demonstrated the feasibility to analyze historical outbreak data with modern analytical tools. However, it also confirmed that predicted epidemics from a most carefully parameterized model cannot integrate all eventualities of a real epidemic. Therefore, decision makers need to be aware that infectious disease models are useful tools to support the decision-making process but their results are not equal valuable as real observations and should always be interpreted with caution.

Evaluation of farm-level parameters derived from animal movements for use in risk-based surveillance programmes of cattle in Switzerland.

BACKGROUND: This study focused on the descriptive analysis of cattle movements and farm-level parameters derived from cattle movements, which are considered to be generically suitable for risk-based surveillance systems in Switzerland for diseases where animal movements constitute an important risk pathway. METHODS: A framework was developed to select farms for surveillance based on a risk score summarizing 5 parameters. The proposed framework was validated using data from the bovine viral diarrhoea (BVD) surveillance programme in 2013. RESULTS: A cumulative score was calculated per farm, including the following parameters; the maximum monthly ingoing contact chain (in 2012), the average number of animals per incoming movement, use of mixed alpine pastures and the number of weeks in 2012 a farm had movements registered. The final score for the farm depended on the distribution of the parameters. Different cut offs; 50, 90, 95 and 99%, were explored. The final scores ranged between 0 and 5. Validation of the scores against results from the BVD surveillance programme 2013 gave promising results for setting the cut off for each of the five selected farm level criteria at the 50th percentile. Restricting testing to farms with a score ≥ 2 would have resulted in the same number of detected BVD positive farms as testing all farms, i.e., the outcome of the 2013 surveillance programme could have been reached with a smaller survey. CONCLUSIONS: The seasonality and time dependency of the activity of single farms in the networks requires a careful assessment of the actual time period included to determine farm level criteria. However, selecting farms in the sample for risk-based surveillance can be optimized with the proposed scoring system. The system was validated using data from the BVD eradication program. The proposed method is a promising framework for the selection of farms according to the risk of infection based on animal movements.

Cost and sensitivity of on-farm versus slaughterhouse surveys for prevalence estimation and substantiating freedom from disease.

Within the framework of Swiss surveillance for epizootic diseases, dairy cattle are sampled using bulk tank milk while non-dairy cattle are sampled on the farm. The latter method is costly, time-demanding and dangerous for the personnel. However, slaughterhouses could be an alternative sampling point for this population. To assess the cost-effectiveness and sensitivity of such an approach, surveillance using slaughterhouse sampling was modelled with data from the 2012 Swiss animal movement database (AMD). We simulated a cross-sectional study for bluetongue (BT), and surveillance programmes to substantiate freedom from infectious bovine rhinotracheitis (IBR) and enzootic bovine leucosis (EBL) (combined) to compare the outcome of random on-farm sampling versus slaughterhouse sampling. We found that, under Swiss conditions, slaughterhouse sampling results in low herd-level sensitivities because animals are sent by owners to slaughter individually and not in large groups, restricting the number of samples per herd. This makes slaughterhouse sampling inappropriate for prevalence surveys at the herd-level. However, for prevalence surveys at the animal-level and for substantiation of freedom from disease, slaughterhouse surveillance is equally or more cost-efficient than on-farm sampling.

Serosurveillance of Schmallenberg virus in Switzerland using bulk tank milk samples.

Infections with Schmallenberg virus (SBV), a novel Orthobunyavirus transmitted by biting midges, can cause abortions and malformations of newborns and severe symptoms in adults of domestic and wild ruminants. Understanding the temporal and spatial distribution of the virus in a certain territory is important for the control and prevention of the disease. In this study, seroprevalence of antibodies against SBV and the spatial spread of the virus was investigated in Swiss dairy cattle applying a milk serology technique on bulk milk samples. The seroprevalence in cattle herds was significantly higher in December 2012 (99.5%) compared to July 2012 (19.7%). This high between-herd seroprevalence in cattle herds was observed shortly after the first detection of viral infections. Milk samples originating from farms with seropositive animals taken in December 2012 (n=209; mean 160%) revealed significantly higher S/P% ratios than samples collected in July 2012 (n=48; mean 103.6%). This finding suggests a high within-herd seroprevalence in infected herds which makes testing of bulk tank milk samples for the identification farms with past exposures to SBV a sensitive method. It suggests also that within-herd transmission followed by seroconversion still occurred between July and December. In July 2012, positive bulk tank milk samples were mainly restricted to the western part of Switzerland whereas in December 2012, all samples except one were positive. A spatial analysis revealed a separation of regions with and without positive farms in July 2012 and no spatial clustering within the regions with positive farms. In contrast to the spatial dispersion of bluetongue virus, a virus that is also transmitted by Culicoides midges, in 2008 in Switzerland, the spread of SBV occurred from the western to the eastern part of the country. The dispersed incursion of SBV took place in the western part of Switzerland and the virus spread rapidly to the remaining territory. This spatial pattern is consistent with the hypothesis that transmission by Culicoides midges was the main way of spreading.

Prevalence of antibodies against bluetongue virus serotype 8 in bulk-tank milk samples from dairy cattle herds located in risk areas for bluetongue virus transmission after a vaccination programme in Switzerland.

Switzerland had been affected by the bluetongue virus serotype 8 (BTV-8) epidemic in Europe in the years 2007 to 2009. After three years of mandatory vaccination and comprehensive surveillance, Switzerland showed to be free of BTV-8 in 2012. In the future Elisa testing of bulk-tank milk (BTM) samples as a very sensitive and cost-effective method should be used for the surveillance of all serotypes of BTV. To determine the prevalence of seropositive herds, BTM from 240 cattle herds was sampled in July 2012. The results showed an apparent seroprevalence of 98.7% in the investigated dairy herds. Most plausible, the high prevalence was caused by the vaccination campaigns rather than by infections with BTV-8. In the outbreak the cumulative number of BTV-8 cases in Switzerland had been 75.Thus it is very likely that the used inactivated vaccines induced long-term antibody titres. Due to the high seroprevalence, investigating for BT-antibodies cannot be used for early recognition of a new introduction of BTV at the moment. Nonetheless, testing of BTM samples is appropriate for an annual evaluation of the seroprevalence and especially as an instrument for early recognition for incursions as soon as the antibody prevalence declines.To determine this decline the BTM testing scheme should be conducted each year as described in this work.

Evaluation of the benefit of emergency vaccination in a foot-and-mouth disease free country with low livestock density.

Foot-and-mouth disease (FMD) is highly contagious and one of the most economically devastating diseases of cloven-hoofed animals. Scientific-based preparedness about how to best control the disease in a previously FMD-free country is therefore essential for veterinary services. The present study used a spatial, stochastic epidemic simulation model to compare the effectiveness of emergency vaccination with conventional (non-vaccination) control measures in Switzerland, a low-livestock density country. Model results revealed that emergency vaccination with a radius of 3 km or 10 km around infected premises (IP) did not significantly reduce either the cumulative herd incidence or epidemic duration if started in a small epidemic situation where the number of IPs is still low. However, in a situation where the epidemic has become extensive, both the cumulative herd incidence and epidemic duration are reduced significantly if vaccination were implemented with a radius of 10 km around IPs. The effect of different levels of conventional strategy measures was also explored for the non-vaccination strategy. It was found that a lower compliance level of farmers for movement restrictions and delayed culling of IPs significantly increased both the cumulative IP incidence and epidemic duration. Contingency management should therefore focus mainly on improving conventional strategies, by increasing disease awareness and communication with stakeholders and preparedness of culling teams in countries with a livestock structure similar to Switzerland; however, emergency vaccination should be considered if there are reasons to believe that the epidemic may become extensive, such as when disease detection has been delayed and many IPs are discovered at the beginning of the epidemic.

Long-term infection of goats with bluetongue virus serotype 25.

Toggenburg Orbivirus (TOV) is the prototype of bluetongue virus serotype 25 (BTV-25). It was first detected in goats in Switzerland in 2008. The virus does not induce clinical signs in infected goats. In field samples viral RNA could be detected only in goats and never in other ruminants. BTV-25 RNA was repeatedly detected for more than one year in the blood of goats from a single flock in Principality of Liechtenstein. Since viral persistence over such a long period has never been reported for bluetongue, blood samples from 110 goats and 2 sheep of that flock were collected during a period of up to two years and analyzed for the presence of BTV-25 RNA and antibodies. Most of the animals which tested positive for BTV-25 RNA, remained positive during the whole investigation period. Moreover, five of these goats were BTV-25 RNA positive over a period of 19-25 months. A weak antibody response against BTV VP7 was commonly observed. As BTV-25 cannot be propagated in any culture system, the presence of virus could only be demonstrated in samples by viral RNA detection using RT-qPCR. To address the question of infectivity of the virus in blood from long-term positive animals, goats were experimentally infected with this blood. Viral replication was demonstrated by increasing RNA amounts. Thus, our findings provide evidence that BTV-25 can persist much longer in an infected host than known so far for other BTV serotypes. Hence, persistence of infectious BTV represents an additional important factor in BTV epidemiology.

Putative risk factors for infections with Toggenburg Orbivirus in goat herds in Southern Switzerland (Canton of Ticino).

Toggenburg Orbivirus (TOV), only detected in goats, has been described as a member of the Bluetongue virus (BTV) serogroup. The transmission pathway of the virus seems different from other Bluetongue viruses (BTVs). The objective of this study was to explore risk factors, especially the influence of alpine pasture and the presence of other livestock species, for the presence of TOV infected goats on farms. Between February 2008 and September 2009, blood samples were collected and analyzed for TOV and hereupon a total of 60 goat farm owners (37 TOV-positive and 23 TOV-negative holdings) were interviewed. Additionally, goatlings were tested for TOV by rRT-PCR prior and after alpine pasture in 2009. These goatlings were positive for TOV only after the alpine pasture. The final logistic regression model included: "exposure to goats from other farms" (OR=10.12, p=0.007), "exposure of the goats to red deer" (OR=4.79, p=0.04) and "exposure to sheep from other farms" (OR=0.05, p=0.002). These variables do not implicitly include direct contact, and the findings are only vaguely indicative for a contact-driven transmission. Furthermore, it is likely that they are only associated with, and thus indicative for, an unknown risk factor associated with alpine pasture not measured in the study. The results of this screening study do not indicate iatrogenic transmission pathways as a main transmission mode and stimulate the formulation of hypotheses on the origin, the transmission pathway and other host species for TOV. Especially, the involvement of an insect vector in transmission on alpine pasture and the relevance of vertical transmission are to be clarified.

Using scenario tree modelling for targeted herd sampling to substantiate freedom from disease.

BACKGROUND: In order to optimise the cost-effectiveness of active surveillance to substantiate freedom from disease, a new approach using targeted sampling of farms was developed and applied on the example of infectious bovine rhinotracheitis (IBR) and enzootic bovine leucosis (EBL) in Switzerland. Relevant risk factors (RF) for the introduction of IBR and EBL into Swiss cattle farms were identified and their relative risks defined based on literature review and expert opinions. A quantitative model based on the scenario tree method was subsequently used to calculate the required sample size of a targeted sampling approach (TS) for a given sensitivity. We compared the sample size with that of a stratified random sample (sRS) with regard to efficiency. RESULTS: The required sample sizes to substantiate disease freedom were 1,241 farms for IBR and 1,750 farms for EBL to detect 0.2% herd prevalence with 99% sensitivity. Using conventional sRS, the required sample sizes were 2,259 farms for IBR and 2,243 for EBL. Considering the additional administrative expenses required for the planning of TS, the risk-based approach was still more cost-effective than a sRS (40% reduction on the full survey costs for IBR and 8% for EBL) due to the considerable reduction in sample size. CONCLUSIONS: As the model depends on RF selected through literature review and was parameterised with values estimated by experts, it is subject to some degree of uncertainty. Nevertheless, this approach provides the veterinary authorities with a promising tool for future cost-effective sampling designs.

Spatial analysis of bluetongue cases and vaccination of Swiss cattle in 2008 and 2009.

Bluetongue (BT) is a vector-borne viral disease of ruminants. The infection is widespread globally with major implications for international animal trade and production. In 2006, BT virus serotype 8 (BTV-8) was encountered in Europe for the first time, causing extensive production losses and death in susceptible livestock. Following the appearance of BTV-8 in Switzerland in 2007, a compulsory vaccination programme was launched in the subsequent year. Due to social factors and difficulties to reach animals on high pasture, the regional vaccination coverage varied across the country in both 2008 and 2009. In this study, the effect of vaccination on the spatial occurrence of BTV-8 and the associated relative disease risk in Switzerland in 2008 and 2009 were investigated by a spatial Bayesian hierarchical approach. Bayesian posterior distributions were obtained by integrated nested Laplace approximations, a promising alternative to commonly used Markov chain Monte Carlo methods. The number of observed BTV-8 outbreaks in Switzerland decreased notably from 2008 to 2009. However, only a non-significant association between vaccination coverage and the probability of a spatial unit being infected with BTV-8 was identified using the model developed for this study. The relative disease risk varied significantly across the country, with a higher relative risk of BTV-8 infection in western and north-western Switzerland where environmental conditions are more suitable for vector presence and viral transmission. Examination of the spatial correlation between disease occurrence, control measures and associated ecological factors can be valuable in the evaluation and development of disease control programmes, allowing prioritisation of areas with a high relative risk of disease.

Surveillance and simulation of bovine spongiform encephalopathy and scrapie in small ruminants in Switzerland.

BACKGROUND: After bovine spongiform encephalopathy (BSE) emerged in European cattle livestock in 1986 a fundamental question was whether the agent established also in the small ruminants' population. In Switzerland transmissible spongiform encephalopathies (TSEs) in small ruminants have been monitored since 1990. While in the most recent TSE cases a BSE infection could be excluded, for historical cases techniques to discriminate scrapie from BSE had not been available at the time of diagnosis and thus their status remained unclear. We herein applied state-of-the-art techniques to retrospectively classify these animals and to re-analyze the affected flocks for secondary cases. These results were the basis for models, simulating the course of TSEs over a period of 70 years. The aim was to come to a statistically based overall assessment of the TSE situation in the domestic small ruminant population in Switzerland. RESULTS: In sum 16 TSE cases were identified in small ruminants in Switzerland since 1981, of which eight were atypical and six were classical scrapie. In two animals retrospective analysis did not allow any further classification due to the lack of appropriate tissue samples. We found no evidence for an infection with the BSE agent in the cases under investigation. In none of the affected flocks, secondary cases were identified. A Bayesian prevalence calculation resulted in most likely estimates of one case of BSE, five cases of classical scrapie and 21 cases of atypical scrapie per 100'000 small ruminants. According to our models none of the TSEs is considered to cause a broader epidemic in Switzerland. In a closed population, they are rather expected to fade out in the next decades or, in case of a sporadic origin, may remain at a very low level. CONCLUSIONS: In summary, these data indicate that despite a significant epidemic of BSE in cattle, there is no evidence that BSE established in the small ruminant population in Switzerland. Classical and atypical scrapie both occur at a very low level and are not expected to escalate into an epidemic. In this situation the extent of TSE surveillance in small ruminants requires reevaluation based on cost-benefit analysis.

Milk concentration improves Bluetongue antibody detection by use of an indirect ELISA.

A national Bluetongue antibody surveillance in cattle through bulk milk was conducted in Switzerland between July 2007 and June 2008. Using ID Screen Bluetongue Milk ELISA (ID VET, Montpellier, France), samples from 15 out of 210 dairy farms at least once gave a positive result. In only three of these herds bluetongue positive animals were found. Therefore, specificity for bulk milk was not as good as expected and when individual milk samples were tested, it was even lower. As further investigations of positive results were time-consuming and no other ELISA was available at that time, we aimed at discriminating false from true positive samples with a confirmatory test using a protein precipitation method followed by retesting with the same ELISA. Additionally, we examined whether testing of single milk samples can reliably be used to assess status of cows, and whether sampling at the beginning or at the end of milking, as well as freezing and thawing of the milk could influence the performance of the test. Screening with ID VET milk ELISA and confirmatory testing after protein precipitation yielded a clear increase of specificity without any loss of sensitivity in both bulk and single milk samples. This testing scheme allowed minimizing follow-up investigations by blood testing. Antibody levels in plasma and milk showed a good correlation. Tested by logistic regression, none of the possible influencing factors (time point of sample collection, freezing, or milk content of the samples) had a significant influence on the test performance.

Risk-based sample size calculation for consecutive surveys to document freedom from animal diseases.

International trade regulations require disease freedom to be documented. This is generally achieved by national random surveys. Risk-based sample size calculations can reduce both the sample size and the costs for repeated surveys by one-third compared to traditional sample size calculations based on random sampling. In this approach, information from previous surveys can reduce the sample size of a new survey while maintaining its overall level of confidence. Risk-based sample size calculations have only formerly been described for one single survey and not when applied consecutively. Based on the existing deterministic origin of risk-based methods and sample size calculations, we devised a further development of sample size calculation to document freedom from non-highly contagious diseases. We show that for a repeated risk-based sample size calculation not only does the loss of confidence due to the risk of disease import and the risk of undetected disease within the country need to be calculated between the two surveys, but the time value of historical testing information also needs to be considered. As the order of surveys is important, a separate process, capable of calculating the time value of information from all conducted surveys, needs to be incorporated in the sample size calculation. This paper suggests how to use information from previous surveys in a risk-based approach for sample size calculations in consecutive surveys considering the adjusted time value of historical testing information, import risk assessments and the risk of disease spread within the country. Thus, the reduction of confidence between two surveys is adequately estimated. The results of sample size calculations for surveys over various years, under different conditions, show that the risk-based approach, including import risk assessments and adjusted time value of historical testing information, could reduce the sample size of annual surveys by 25% compared to the sample sizes calculated without a risk-based technique. The presented risk-based sample size calculation is appropriate for the requirements of consecutive surveys and outlines how the adjusted time value of historical testing information should be considered in this context. When planning to undertake repeated surveys to document freedom from disease, this method can easily be used to calculate sample sizes and consequently reduce them.

Establishing a cost-effective national surveillance system for Bluetongue using scenario tree modelling.

Vector-borne diseases pose a special challenge to veterinary authorities due to complex and time-consuming surveillance programs taking into account vector habitat. Using stochastic scenario tree modelling, each possible surveillance activity of a future surveillance system can be evaluated with regard to its sensitivity and the expected cost. The overall sensitivity of various potential surveillance systems, composed of different combinations of surveillance activities, is calculated and the proposed surveillance system is optimized with respect to the considered surveillance activities, the sensitivity and the cost. The objective of this project was to use stochastic scenario tree modelling in combination with a simple cost analysis in order to develop the national surveillance system for Bluetongue in Switzerland. This surveillance system was established due to the emerging outbreak of Bluetongue virus serotype 8 (BTV-8) in Northern Europe in 2006. Based on the modelling results, it was decided to implement an improved passive clinical surveillance in cattle and sheep through campaigns in order to increase disease awareness alongside a targeted bulk milk testing strategy in 200 dairy cattle herds located in high-risk areas. The estimated median probability of detection of cases (i.e. sensitivity) of the surveillance system in this combined approach was 96.4%. The evaluation of the prospective national surveillance system predicted that passive clinical surveillance in cattle would provide the highest probability to detect BTV-8 infected animals, followed by passive clinical surveillance in sheep and bulk milk testing of 200 dairy cattle farms in high-risk areas. This approach is also applicable in other countries and to other epidemic diseases.

Field performance of two rapid screening tests in active surveillance of transmissible spongiform encephalopathies in small ruminants.

Recently, screening tests for monitoring the prevalence of transmissible spongiform encephalopathies specifically in sheep and goats became available. Although most countries require comprehensive test validation prior to approval, little is known about their performance under normal operating conditions. Switzerland was one of the first countries to implement 2 of these tests, an enzyme-linked immunosorbent assay (ELISA) and a Western blot, in a 1-year active surveillance program. Slaughtered animals (n = 32,777) were analyzed in either of the 2 tests with immunohistochemistry for confirmation of initial reactive results, and fallen stock samples (n = 3,193) were subjected to both screening tests and immunohistochemistry in parallel. Initial reactive and false-positive rates were recorded over time. Both tests revealed an excellent diagnostic specificity (>99.5%). However, initial reactive rates were elevated at the beginning of the program but dropped to levels below 1% with routine and enhanced staff training. Only those in the ELISA increased again in the second half of the program and correlated with the degree of tissue autolysis in the fallen stock samples. It is noteworthy that the Western blot missed 1 of the 3 atypical scrapie cases in the fallen stock, indicating potential differences in the diagnostic sensitivities between the 2 screening tests. However, an estimation of the diagnostic sensitivity for both tests on field samples remained difficult due to the low disease prevalence. Taken together, these results highlight the importance of staff training, sample quality, and interlaboratory comparison trials when such screening tests are implemented in the field.

Surveillance of H5 avian influenza virus in wild birds found dead.

Wild birds are suspected to play a role in the spread of avian influenza H5N1; however, much remains unknown about the ecology and epidemiology of H5N1 in wild birds. Lake Constance is an important wetland area and was a focus for surveillance of dead wild birds between February and June 2006. Dead wild birds collected from the lake and surrounding regions were tested for avian influenza H5. This article provides a descriptive and spatial analysis of the data collected during this period and includes discussion of the strengths and limitations of this type of surveillance. The sampling of dead birds may provide a rapid and cost-effective means of detecting the presence of H5N1; however, such sampling is prone to certain biases and lacks sensitivity in detecting asymptomatic infections. The benefit of such surveillance will be enhanced by detailed ornithologic information, greater accuracy of spatially referenced data, and quantification of surveillance effort.

Comparison of the historic recycling risk for BSE in three European countries by calculating the basic reproduction ratio R0.

A deterministic model of BSE transmission is used to calculate the R(0) values for specific years of the BSE epidemics in the United Kingdom (UK), the Netherlands (NL), and Switzerland (CH). In all three countries, the R(0) values decreased below 1 after the introduction of a ban on feeding meat and bone meal (MBM) to ruminants around the 1990s. A variety of additional measures against BSE led to further decrease of R(0) to about 0.06 in the years around 1998. The calculated R(0) values were consistent with the observations made on the surveillance results for UK, but were partially conflicting with the surveillance results for NL and CH. There was evidence for a dependency of the BSE epidemic in NL and CH from an infection source not considered in the deterministic transmission model. Imports of MBM and feed components can be an explanation for this discrepancy, and the importance of imports for these observations is discussed.