Quantitative analysis of 33 benzodiazepines, metabolites and benzodiazepine-like substances in whole blood by liquid chromatography-(tandem) mass spectrometry.

A quantitative method using high-performance liquid chromatography-mass spectrometry (LC-MS, ion trap) after matrix supported liquid-liquid extraction is described for the simultaneous determination in whole blood of 33 benzodiazepines including metabolites and benzodiazepine-like substances. The limits of detection (LOD) range from 0.0001 to 0.0126 mg/l. Linearity is satisfactory for all compounds. The extraction recoveries for the benzodiazepines in whole blood are between 60 and 91%, desmethyldiazepam, OH-bromazepam and brotizolam excepted. Selectivity, accuracy and precision are satisfactory for clinical and forensic purposes.

Computer simulation to support policy making in the control of pseudorabies.

A further integration of international markets makes a coordinated policy against contagious animal infections increasingly important. In the future, stricter demands are to be expected concerning the control and eradication of such infections. To anticipate these demands, a computer simulation model is created in which scenarios can be evaluated with respect to epidemiological and economic effects of the infections and control strategies. In this paper, the simulation model is described for Pseudorabies in swine. In the model, the population of herds is subdivided into two main herd types: breeding and finishing. Each herd is in one of 24 states per herd type. The states are based on (1) the reproduction ratio R which is the number of secondary cases caused by one infectious herd, (2) the prevalence for each value of R and (3) the expected number of infectious animals in an infectious herd within each prevalence range and for each R. The different values of R are based on experiments and field data in which different vaccination strategies were used. The transition matrix with the probabilities of every transition from one state to another is calculated on a weekly base. With this matrix the distribution of herds over states from week to week is derived. To include a dynamic element in the transition probabilities, the number of newly infectious herds per week is a function of animal and other contacts, including aerial, material and personal contacts. Calculations show that the infection in the Dutch swine population will not disappear without vaccination. With a vaccination scheme in which sows are vaccinated 3 times per year and fattening pigs 1 time per cycle the infection will ultimately be eradicated, but 2 vaccinations per cycle for fattening pigs are needed to eradicate the infection within an acceptable timespan (i.e. 2 to 3 years). The latter strategy will become compulsory in the Netherlands from October 1st 1995.

An economic model for on-farm decision support of management to prevent infectious disease introduction into dairy farms.

A more-closed farming system can be a good starting point for eradication of infectious diseases from within a herd. The economic implications of a more-closed farming system will not always be obvious to farmers. The management decisions are related to different parts of the farm and are farm-specific. To support these decisions, a model was developed of the economic consequences of a more-closed system (a simple static and deterministic design was used). The risk factors in the model were based solely on bovine herpesvirus type 1 (BHV1) but losses due to introduction of BVDV, L. hardjo, and S. dublin were added to the model. The model was verified and partly validated and a sensitivity analysis was done. The cost to one 55-cow dairy farm that refrained from purchasing cattle, provided protective clothing to professional visitors and a temporary employee, and built and maintained a double fence around 6 ha of land to prevent over-the-fence contacts was Dfl. 4495 over 5 years. The probability of disease introduction was decreased by 74%. The prevented losses for disease introduction amounted to Dfl. 7033 over 5 years (net benefits of Dfl. 2538 over 5 years).A more-closed system would be still beneficial when a sanitary barrier was used instead of just protective clothing, when the probability of introduction of infectious diseases was decreased, and when odds ratios in the model were replaced by more-conservative relative risks. The benefits became negative when a farm had to build and maintain a double fence around 12 ha instead of 6 ha, when the probability of introduction of all diseases was decreased by 50%, and when the estimations were based solely on BHV1.

Repeatability in ranking of dairy farms on technical and economic performance over years.

Repeatability of farm average 305-day milk production and gross margin per 100 kg of milk was evaluated for 39 farms. Ranking of gross margin, its underlying factors (i.e. milk price, returns from cull cows and calves, costs of concentrates, and costs of roughage purchases per 100 kg of milk), and 305-day milk production was not completely random over the four years of the study. The coefficient of concordance ranged between 0.55 and 0.82. The costs of roughage purchased had the lowest concordance over time, and 305-day milk production had the highest concordance. For each year and each farm, the difference between average gross margin and farm-specific gross margin was calculated. The standard deviations (SD) of these values was calculated for each farm, and showed differences between farms in variability in gross margin over years (the farm-year-specific SD varied between farms from 0.56 to 5.73). All the underlying factors showed a deviation over years. So, variability of gross margin can be due to changes in all underlying factors. The impact on gross margin of purchased roughage was not of major importance because its absolute impact on the gross margin is small. We concluded that milk-production data over one year is a reliable indicator for the typical farm milk production. Because gross margin fluctuates considerably over time, however it is preferred to base economic research on data from more than one year.

Quantifying characteristics of information-technology applications based on expert knowledge for detection of oestrus and mastitis in dairy cows.

Expert opinions were elicited about the characteristics at the commercial-farm level of on-line information technology (IT) applications that are able to detect oestrus and mastitis in dairy cows. Since actual data of these characteristics are not available, judgmental data provided an alternative means to interpret the implications of research results for commercial farms. Applications included were activity measurement, milk-production measurement, electrical conductivity of quarter milk, automated concentrate feeders and milk-temperature measurement. Sensitivity and specificity of detection of oestrus (OD), clinical-mastitis (CMD) and subclinical-mastitis (SCMD) were ascertained. Conjoint-analysis was used to assess the effect of each application indirectly by decomposing the evaluated overall detection characteristics of a predefined number of IT combinations. The individual experts were consistent in evaluating the alternatives, but there was variation in estimates among experts. Estimations of the main effects of the applications and important first-order interactions were incorporated into the detection models. Implementation of all applications under study resulted in overall sensitivities and specificities of 82% and 90%, 73% and 87%, 58% and 82% for OD, CMD and SCMD, respectively. Further research is necessary that should take into account costs and benefits of the different detection systems based on the current status of farm performance (e.g. OD and mastitis incidence) and farm structure (e.g. farm size, years in operation of the milking parlour and parlour layout). Research to do this is currently in progress.

Adaptive conjoint analysis to determine perceived risk factors of farmers, veterinarians and AI technicians for introduction of BHV1 to dairy farms.

A study was carried out to determine the possibility of a more-closed farming system for (Dutch) dairy farms. The objective of the study was to provide effective and economically profitable management advice for improving the animal-health status of farms. Management measures will only be successfully applied if supported by farmers and their advisors (such as veterinarians). Therefore, the perception of farmers and advisors of the importance of various risk factors for the introduction of diseases to a farm was determined by using bovine herpes virus type 1 (BHV1) as an example. As part of the study, an evening-long workshop was organized and run thrice. In total, 49 farmers, veterinarians and AI technicians participated in these workshops. The computerized questionnaire technique was based on adaptive conjoint analysis (ACA). ACA has the advantage that participants can work with a large number of risk factors in a relatively short period of time. Another advantage of ACA (compared with standard questionnaires) is that the answers from each participant can be checked with regard to consistency with respect to the importance assigned to them. Data from participants with inconsistent responses can be excluded from further analyses. The results of the ACA interview were compared with the risk factors reported in the literature as being associated with BHV1 status (e.g. purchase of cattle, participation in cattle shows) and with farmers' actual management to prevent the introduction of diseases. The workshop participants were all operating in the dairy sector and they seemed well aware of the risk of direct animal contacts for the introduction of BHV1. Farmers thought visitors to be more risky than did AI technicians and (especially) veterinarians. Farmers who purchased cattle or participated in cattle shows were of the opinion that the risks of direct animal contacts were more important than did farmers who were not involved in those practices. Farmers whose farms were BHV1-positive (and participated in cattle shows more often) thought the risk of participation smaller than did farmers with BHV1-negative farms.

Probability of and risk factors for introduction of infectious diseases into Dutch SPF dairy farms: a cohort study.

A 2-year cohort study was conducted to investigate the probability of disease introduction into Dutch dairy farms. The farms were tested regularly for diseases and were visited biannually to collect management data. Ninety-five specific pathogen-free (SPF) dairy farms were selected from a database of bovine herpesvirus type 1 (BHV1)-free farms to study the probability of, and risk factors for, introduction of BHV1, bovine viral diarrhoea virus (BVDV), Salmonella enterica subsp. enterica serotype Dublin (S. dublin), and Leptospira interrogans serovar hardjo (L. hardjo). Although most of the 95 SPF farms had a low risk on introduction of infectious diseases, one disease was introduced into 12 farms and two diseases were introduced into one farm. Three farms experienced an outbreak of BHV1, one farm an outbreak of L. hardjo, two farms BVDV, six farms S. dublin, and one farm both BHV1 and S. dublin. The total incidence rate was 0.09 (0.06-0.12) per herd-year at risk. The results suggest that the "non-outbreak" farms were significantly more closed than the "outbreak" farms. Direct animal contacts with other cattle should be avoided and professional visitors should be instructed to wear protective clothing before handling cattle.

Monte Carlo simulation of virus introduction into the Netherlands.

In order to improve the understanding of the risk of introducing classical swine fever (CSF) and foot-and-mouth disease (FMD) into the Netherlands, a Monte Carlo simulation model was developed. The model, VIRiS (Virus Introduction Risk Simulation model) describes virus introduction into the Netherlands from outbreaks in other European countries. VIRiS is aimed at supporting decision makers involved in disease prevention. The model is based on historical and experimental data, supplemented with expert judgement, and provides the expected number, location and cause of primary outbreaks in the Netherlands. The paper gives a detailed description of the design and behaviour of VIRiS. The default outcomes of VIRiS show that in the current situation, the western and northern regions of the Netherlands are most prone to outbreaks of CSF and FMD. Most outbreaks originate from the countries neighbouring the Netherlands and the countries of southern Europe. Several alternative prevention strategies were evaluated using a combination of the VIRiS model and models describing the spread and economic consequences of outbreaks. A considerable financial window is available for measures aimed at speeding up the detection of epidemics in countries from which a Dutch outbreak may originate. Complete elimination of the risk associated with the risk factor 'returning trucks' reduces the annual losses due to FMD and CSF epidemics by approximately US$ 9 million. The approach is general and could also be applied to other diseases and countries.

Relationships between dairy cow mastitis and fertility management and farm performance.

A field study was carried out on 38 dairy farms in the Netherlands to determine the relationship between mastitis and fertility management with 305-day milk production and gross margin. Questionnaires were used to get insight into the farmers' management. Out of 150 variables related to mastitis and fertility management, and technical and economic results, 44 variables were selected based on correlation of > or = 0.25 or < or = -0.25 with milk production and/or gross margin. These variables were used in two separate partial least squares (PLS) analyses. PLS has the advantage that it can handle a large number of variables in relation to the number of cases. The PLS-model of 305-day milk production had R2 = 0.54 and showed a positive relation between 305-day milk production and awareness of the farmer regarding bulk somatic-cell count (BSCC), the goal level of the farmer for BSCC, and hygiene of the milking parlour. Fertility was negatively related to 305-day milk production, in spite of a relatively good fertility management on high-producing farms. R2 = 0.46 for gross margin. The aspiration level of fertility did not seem to affect gross margin, but awareness of BSCC and calving interval (CI) had positive effects. Such awareness seemed a general parameter for good economic results, because it was correlated with different aspects of gross margin.

Economic evaluation of national identification and recording systems for pigs in Belgium.

Four national identification and recording (I&R) systems for the Belgian pig industry were evaluated economically, using a computer simulation model. These systems were: (1) the previous system; (2) a revised system (based on the previous one); (3) a system based on electronic identification; (4) a system similar to (3) but which also allows electronic monitoring of individual pigs. The evaluation of the systems particularly concerned their use in the control of classical swine fever (CSF). Four factors have shown to be very influential in economic decision making with respect to I&R systems: (1) the economic losses per CSF epidemic; (2) the frequency of CSF epidemics; (3) the operational costs of the I&R system; (4) the possibility of additional use of the system besides CSF control. It was concluded that for the Belgian situation, replacement of the previous I&R system by the revised one is economically justifiable. Because of high operational costs, electronic identification systems are only economically feasible in very specific situations, e.g. when a higher degree of additional use is possible or with a relatively high frequency of CSF epidemics.

Spatial and stochastic simulation to compare two emergency-vaccination strategies with a marker vaccine in the 1997/1998 Dutch Classical Swine Fever epidemic.

Two alternative emergency-vaccination strategies with a marker vaccine that could have been applied in the 1997/1998 Dutch Classical Swine Fever (CSF) epidemic were evaluated in a modified spatial, temporal and stochastic simulation model: InterCSF. In strategy 1, vaccination would be applied only to overcome a shortage in destruction capacities. Destruction of all pigs on vaccinated farms distinguishes this strategy from strategy 2, which assumes intra-Community trade of vaccinated pig meat. InterCSF simulates the spread of CSF between farms through local spread and three contact types. Disease spread is affected by control measures implemented through different mechanisms. Economic results were generated by a separate model that calculated the direct costs (including the vaccination costs) and consequential losses for farmers and related industries subjected to control measures. The comparison (using epidemiological and economic results) between the different emergency-vaccination strategies with an earlier simulated preventive-slaughter scenario led to some general conclusions on the Dutch CSF epidemic. Both emergency-vaccination strategies were hardly more efficient than the non-vaccination scenario. The intra-Community trade strategy (vaccination-strategy 2) was the least costly of all three scenarios.

An epidemiological and economic simulation model to evaluate the spread and control of infectious bovine rhinotracheitis in The Netherlands.

Bovine herpesvirus type I (BHV1), causing infectious bovine rhinotracheitis (IBR), was introduced in the Netherlands in 1971. In 1993, about 42% of the dairy cows had antibodies against BHV1. In the future, stricter requirements are anticipated regarding the health status of exported breeding cows and material. To support policymakers in their decisions on IBR eradication, a simulation model was developed in which the epidemiological and economic consequences of various control strategies were evaluated. This paper describes the model and provides an overview of some important outcomes. In the model, dairy herds were classified into different disease states based on (1) the reproduction ratio of the disease (R, defined as the number of secondary cases caused by one infectious animal) (2) the within-herd prevalence, within each value of R and (3) the expected number of infectious animals in an infectious herd within each prevalence range. The dynamic transition probability of a herd going from one state to another per week depends on direct contacts between animals, and other contacts such as transmission through fomites, indirect transmission through other species, airborne transmission and minor disease-specific routes such as venereal or iatrogenic transmission. Five control strategies, including both a voluntary vaccination program and a compulsory vaccination program for all dairy herds were evaluated. A voluntary vaccination program with 50% participation is not expected to lead to eradication of IBR. It appears that compulsory vaccination would be necessary to reach an IBR-free status.

A model to estimate the financial consequences of classical swine fever outbreaks: principles and outcomes.

A model is presented aimed at a financial analysis of a Classical Swine Fever outbreak. Financial consequences are calculated for affected parties, including governments (EU and national), farms, and related industries in the production chain. The model can be used to calculate the losses of a real outbreak as well as of a simulated one. In this article, the model is applied to the 1997/1998 outbreak of Classical Swine Fever in the Netherlands. Results show that total financial consequences of the outbreak are US $2.3 billion. Consequential losses for farmers and related industries are US $423 million and US $596 million respectively. Budgetary consequences for governments include less than 50% of the total losses calculated by the model. The model can be adapted easily to suit other diseases and countries.

Spatial and stochastic simulation to evaluate the impact of events and control measures on the 1997-1998 classical swine fever epidemic in The Netherlands. I. Description of simulation model.

The simulation model InterCSF was developed to simulate the Dutch Classical Swine Fever (CSF) epidemic of 1997-98 as closely as possible. InterCSF is a spatial, temporal and stochastic simulation model. The outcomes of the various replications give an estimate of the variation in size and duration of possible CSF-epidemics. InterCSF simulates disease spread from an infected farm to other farms through three contact types (animals, vehicles, persons) and through local spread up to a specified distance. The main disease-control mechanisms that influence the disease spread in InterCSF are diagnosis of the infected farms, depopulation of infected farms, movement-control areas, tracing, and pre-emptive slaughter. InterCSF was developed using InterSpread as the basis. InterSpread was developed for foot-and-mouth disease (FMD). This paper describes the process of modifying InterSpread into InterCSF. This involved changing the assumptions and mechanisms for disease spread from FMD to CSF. In addition, CSF-specific control measures based on the standard European Union (EU) regulations were included, as well as additional control measures that were applied during the Dutch epidemic. To adapt InterCSF as closely as possible to the Dutch 1997/98 epidemic, data from the real epidemic were analysed. Both disease spread and disease-control parameters were thus specifically based on the real epidemic. In general, InterSpread turned out to be a flexible tool that could be adapted to simulate another disease with relative ease. The most difficult were the modifications necessary to mimic the real epidemic as closely as possible. The model was well able to simulate an epidemic with a similar pattern over time for number of detected farms as the real outbreak; but the absolute numbers were (despite many relevant modifications) not exactly the same--but were within an acceptable range. Furthermore, the development of InterCSF provided the researchers with a better insight into the existing knowledge gaps. In part II (see the final paper in this issue), InterCSF was used to compare various control strategies as applied to this epidemic.

Spatial and stochastic simulation to evaluate the impact of events and control measures on the 1997-1998 classical swine fever epidemic in The Netherlands. II. Comparison of control strategies.

Using the spatial, temporal and stochastic simulation model InterCSF, several alternative pre-emptive slaughter strategies that could have been applied in the Dutch Classical Swine Fever (CSF) epidemic of 1997-1998 were evaluated. Furthermore, effects of changes in some disease-spread and disease-control parameters were studied. InterCSF simulates the spread of CSF between farms through local spread and contacts (animals, transport and persons). Disease spread is affected by control measures implemented through different mechanisms (e.g. depopulation of infected farms, pre-emptive slaughter, movement control). The starting point for the evaluation of strategies was a simulated basic scenario, which mimicked the real epidemic. Strategies were compared using epidemiological as well as economic results. Economic results were generated by a separate model (EpiLoss) that calculated the direct losses and consequential losses for farmers and related industries. The comparison of the different alternatives to the basic scenario led to some general conclusions on the Dutch CSF-epidemic. Pre-emptive slaughter seemed to be an effective strategy to reduce the size of an epidemic, if started at an early stage. Economically, pre-emptive slaughter was not as expensive as expected; the resulting smaller size of the epidemic, combined with less welfare slaughter, led to much lower overall losses. Furthermore, although large movement control areas seemed effective in reducing the size of the epidemic, the total losses were relatively high because of subsequent welfare slaughter. If infection probabilities could be reduced, for example by improved biosecurity, the resulting epidemics would be much smaller.

Evaluating control strategies for outbreaks in BHV1-free areas using stochastic and spatial simulation.

Several countries within the EU have successfully eradicated bovine herpesvirus type I (BHV1), while others are still making efforts to eradicate the virus. Reintroduction of the virus into BHV1-free areas can lead to major outbreaks - thereby causing severe economic losses. To give decision-makers more insight into the risk and economic consequences of BHV1 reintroduction and into the effectiveness of various control strategies, we developed the simulation model InterIBR. InterIBR is a dynamic model that takes into account risk and uncertainty and the geographic location of individual farms. Simulation of a BHV1-outbreak in the Netherlands starts with introduction of the virus on a predefined farm type, after which both within-farm and between-farm transmission are simulated. Monitoring and control measures are implemented to simulate detection of the infection and subsequent control. Economic consequences included in this study are related to losses due to infection and costs of control. In the simulated basic control strategy, dairy farms are monitored by monthly bulk-milk tests and miscellaneous farms are monitored by half-yearly serological tests. After detection, movement-control measures apply, animal contacts are traced and neighbour farms are put on surveillance. Given current assumptions on transmission dynamics, we conclude that a strategy with either rapid removal or vaccination of infected cattle does not reduce the number of infected farms compared to this basic strategy - but will cost more to control. Farm type with first introduction of BHV1 has a considerable impact on the expected number of secondarily infected farms and total costs. To limit the number of infected farms and total costs due to outbreaks, we suggest intensifying the monitoring program on farms with a high frequency of cattle trade, and monthly bulk-milk testing on dairy farms.

Risk factors for existence of Bovine Herpes Virus 1 antibodies on nonvaccinating Dutch dairy farms.

A more closed farming system may prevent introduction of infectious diseases on dairy farms and can be a good starting point for control of these diseases. Data were available on the presence of Bovine Herpes Virus 1 (BHV1) antibodies in bulk milk and/or blood samples of Dutch dairy farms. Furthermore, information about the possible risk factors for introduction of infectious diseases was collected on 214 of these dairy farms. Data of 107 farms which had been never vaccinated against BHV1 remained for the analysis. A positive BHV1 status on these 107 farms could only be caused by introduction of BHV1. Risk factors for introduction of BHV1 on the farms were quantified using logistic regression. BHV1-positive farms purchased cattle and participated in cattle shows more often compared with BHV1-negative farms. A BHV1-positive farm also had more (professional) visitors in the barn who used farm clothing less often. The BHV1-positive farms were found to be situated closer to other cattle farms compared with the BHV1-negative farms.

Use of AI technician scores for body condition, uterine tone and uterine discharge in a model with disease and milk production parameters to predict pregnancy risk at first AI in Holstein dairy cows.

Technicians recorded body condition score (BCS) and several parameters related to estrus and/or metritis for 1694 first insemination cows on 23 farms. Additional variables for modeling the adjusted odds ratios (OR) for pregnancy were data on disease prior to or within 21 days of AI and test day milk yields. Significant predictors for pregnancy were farm, year and season, BCS, uterine tone, contaminated insemination gun after AI, fat-protein corrected kilograms milk (FPCM), days in milk (DIM), and diseases. Vaginal mucus, ease of cervical passage, and lameness were not significant predictors for pregnancy. Pregnancy risk at AI increased with increasing DIM, reaching a near optimum after 82 days. Lack of uterine tone was associated with a lowered pregnancy risk (OR = 0.69) as was contaminated insemination gun (OR = 0.67), first-parity lactation, FPCM >33 kg (OR = 0.71), BCS 2.5 at AI (OR = 0.65), clinical mastitis (OR = 0.53), cystic ovarian disease (OR = 0.53), and metritis (OR = 0.74). It was concluded that data on BCS and uterine findings, as collected by AI technicians, are significant predictors of AI outcome. Dairy producers and veterinarians should jointly examine the potential costs and value of such AI technician-based data to improve herd fertility.

Risks and economic consequences of introducing classical swine fever into The Netherlands by feeding swill to swine.

An effective animal disease prevention and eradication programme is of great importance for meat-exporting countries such as the Netherlands. If a serious outbreak of disease were to occur, the eradication measures required by the European Union and a possible ban on meat exports would have severe economic consequences. However, historical and experimental information on which these programmes can be based is scarce. Furthermore, until recently, an integrated approach which combined the various aspects of outbreaks and risks with economic consequences was lacking. This paper describes a project based on such an integrated approach. The project covered the elicitation of expert knowledge and the development of the virus introduction risk simulation model (VIRiS). VIRiS integrates objective and subjective information concerning risks and consequences of virus introduction, and thus presents policy-makers with a useful tool for the evaluation of existing prevention programmes and possible alternatives. VIRiS is illustrated for classical swine fever. A comparison is made between the current situation and a hypothetical situation where the risk factor 'swill feeding' is completely eliminated.

The risk of the introduction of classical swine fever virus at regional level in the European Union: a conceptual framework.

Recent classical swine fever (CSF) epidemics in the European Union (EU) have clearly shown that preventing the introduction of CSF virus (CSFV) deserves high priority. Insight into all the factors contributing to the risk of CSFV introduction is a prerequisite for deciding which preventive actions are cost-effective. The relations between virus introduction and spread, prevention and control, and economic losses have been described using the conceptual framework presented in this paper. A pathway diagram provides insight into all the pathways contributing to the likelihood of CSFV introduction (LVI_CSF) into regions of the EU. A qualitative assessment based on this pathway diagram shows that regions with high pig densities generally have a higher LVI_CSF, although this cannot be attributed to pig density only. The pathway diagram was also used to qualitatively assess the reduction in LVI_CSF achieved by restructuring the pig production sector. Especially integrated chains of industrialised pig farming reduce the LVI_CSF considerably, but are also difficult and costly to implement. Quantitative assessment of the LVI_CSF on the basis of the pathway diagram is needed to support the results of the qualitative assessments described.