Classical Swine Fever Epidemics Research Articles

Estimation of the Lethality Rate, Recovery Rate, and Case Fatality Ratio of Classical Swine Fever in Japanese Wild Boar: An Analysis of the Epidemics From September 2018 to March 2019.

Understanding the morbidity and lethality of diseases is necessary to evaluate the effectiveness of countermeasure against the epidemics (e.g., vaccination). To estimate them, detailed data on host population dynamics are required; however, estimating the population size for wildlife is often difficult. We aimed to elucidate the morbidity and lethality of classical swine fever (CSF) currently highly prevalent in the wild boar population in Japan. To this end, we estimated lethality rate, recovery rate, and case fatality ratio (CFR) of CSF without detailed data on the population estimates of wild boar. A mathematical model was constructed to describe the CSF dynamics and population dynamics of wild boar. We fitted the model to the (i) results of the reverse transcription polymerase chain reaction (RT-PCR) test for the CSFV gene and the (ii) results of the enzyme-linked immunosorbent assay (ELISA) test for the antibody against CSFV in sampled wild boar. In the 280 wild boar sampled from September 2018 to March 2019 in the major CSF-affected area in Japan, the lethality rate and recovery rate of CSF per week were estimated as 0.165 (95% confidence interval: 0.081–0.250) and 0.004 (0–0.009), respectively. While the estimate of lethality rate of CSF was similar with the estimates in previous studies, the recovery rate was lower than those reported previously. CFR was estimated as 0.959 (0.904–0.981) using our estimate of recovery rate. This study is the first to estimate lethality rate of CSF from the dynamics of CSF epidemics in the wild boar population. Since the value of CFR is sensitive to the value of recovery rate, the accuracy in the estimate of recovery rate is a key for the accurate estimation of CFR. A long-term transmission experiment of moderately virulent strains may lead to more accurate estimation of the recovery rate and CFR of CSF.

Space-time cluster analysis to improve classical swine fever risk-based surveillance in Ecuador

Space-time cluster analysis to improve classical swine fever risk-based surveillance in Ecuador

Implementation and validation of an economic module in the Be-FAST model to predict costs generated by livestock disease epidemics: Application to classical swine fever epidemics in Spain

Be-FAST is a computer program based on a time-spatial stochastic spread mathematical model for studying the transmission of infectious livestock diseases within and between farms. The present work describes a new module integrated into Be-FAST to model the economic consequences of the spreading of classical swine fever (CSF) and other infectious livestock diseases within and between farms. CSF is financially one of the most damaging diseases in the swine industry worldwide. Specifically in Spain, the economic costs in the two last CSF epidemics (1997 and 2001) reached jointly more than 108 million euros. The present analysis suggests that severe CSF epidemics are associated with significant economic costs, approximately 80% of which are related to animal culling. Direct costs associated with control measures are strongly associated with the number of infected farms, while indirect costs are more strongly associated with epidemic duration. The economic model has been validated with economic information around the last outbreaks in Spain. These results suggest that our economic module may be useful for analysing and predicting economic consequences of livestock disease epidemics.

Simulation of Cross-border Impacts Resulting from Classical Swine Fever Epidemics within the Netherlands and Germany.

The cross-border region of the Netherlands (NL) and the two German states of North Rhine Westphalia (NRW) and Lower Saxony (LS) is a large and highly integrated livestock production area. This region increasingly develops towards a single epidemiological area in which disease introduction is a shared veterinary and, consequently, economic risk. The objectives of this study were to examine classical swine fever (CSF) control strategies' veterinary and direct economic impacts for NL, NRW and LS given the current production structure and to analyse CSF's cross-border causes and impacts within the NL-NRW-LS region. The course of the epidemic was simulated by the use of InterSpread Plus, whereas economic analysis was restricted to calculating disease control costs and costs directly resulting from the control measures applied. Three veterinary control strategies were considered: a strategy based on the minimum EU requirements, a vaccination and a depopulation strategy based on NL and GER's contingency plans. Regardless of the veterinary control strategy, simulated outbreak sizes and durations for 2010 were much smaller than those simulated previously, using data from over 10 years ago. For example, worst-case outbreaks (50th percentile) in NL resulted in 30-40 infected farms and lasted for two to four and a half months; associated direct costs and direct consequential costs ranged from €24.7 to 28.6 million and €11.7 to 26.7 million, respectively. Both vaccination and depopulation strategies were efficient in controlling outbreaks, especially large outbreaks, whereas the EU minimum strategy was especially deficient in controlling worst-case outbreaks. Both vaccination and depopulation strategies resulted in low direct costs and direct consequential costs. The probability of cross-border disease spread was relatively low, and cross-border spread resulted in small, short outbreaks in neighbouring countries. Few opportunities for further cross-border harmonization and collaboration were identified, including the implementation of cross-border regions (free and diseased regions regardless of the border) in case of outbreaks within close proximity of the border, and more and quicker sharing of information across the border. It was expected, however, that collaboration to mitigate the market effects of an epidemic will create more opportunities to lower the impact of CSF outbreaks in a cross-border context.

The potential of antiviral agents to control classical swine fever: A modelling study

Classical swine fever (CSF) represents a continuous threat to pig populations that are free of disease without vaccination. When CSF virus is introduced, the minimal control strategy imposed by the EU is often insufficient to mitigate the epidemic. Additional measures such as preemptive culling encounter ethical objections, whereas emergency vaccination leads to prolonged export restrictions. Antiviral agents, however, provide instantaneous protection without inducing an antibody response. The use of antiviral agents to contain CSF epidemics is studied with a model describing within- and between-herd virus transmission. Epidemics are simulated in a densely populated livestock area in The Netherlands, with farms of varying sizes and pig types (finishers, piglets and sows).Our results show that vaccination and/or antiviral treatment in a 2km radius around an infected herd is more effective than preemptive culling in a 1 km radius. However, the instantaneous but temporary protection provided by antiviral treatment is slightly less effective than the delayed but long-lasting protection offered by vaccination. Therefore, the most effective control strategy is to vaccinate animals when allowed (finishers and piglets) and to treat with antiviral agents when vaccination is prohibited (sows). As independent control measure, antiviral treatment in a 1km radius presents an elevated risk of epidemics running out of control. A 2km control radius largely eliminates this risk.

Control of Classical Swine Fever Epidemics Under Varying Conditions - With Special Focus on Emergency Vaccination and Rapid PCR Testing

In case of a classical swine fever outbreak in the European Union (EU), its control is based upon the culling of swine on infected farms, movement restrictions in the protection and surveillance zones, and contact tracing. Additionally, preventive culling may be carried out. Emergency vaccination and rapid PCR testing are discussed as alternatives to avoid this measure. An outbreak of classical swine fever and the success of its control are influenced by different factors. Using a spatial and temporal Monte-Carlo simulation model the control strategies 'Restriction Zone', 'Traditional Control', 'Emergency Vaccination', 'Test To Slaughter', 'Test To Control' and 'Vaccination in conjunction with Rapid Testing' were compared under various conditions. Farm density, compliance with movement restrictions and delay in the establishment of an emergency vaccination were analysed as influencing factors. It was found that all these factors had a significant influence on the number of infected and culled farms. In a low-density region, the basic measures are sufficient to control an epidemic, provided strict compliance with movement restrictions is adhered to. In a high-density region, additional measures are necessary. They can compensate non-strict compliance with movement restriction to a certain extent. In the high-density region, 'Emergency Vaccination' and 'Vaccination in conjunction with Rapid Testing' reached the same level of infected farms as 'Traditional Control', independent of the value of compliance with movement restrictions. However, in the case of an emergency vaccination, an early start to the vaccination campaign is essential for successful disease control.

Modelling the spread of Swine Vesicular Disease Virus and Vesicular Stomatitis Virus in an area of livestock units without any control measures and measurement of consequential impact resulting from an assumed introduction into one livestock farm

EFSA Supporting PublicationsVolume 9, Issue 5 285E External scientific reportOpen Access Modelling the spread of Swine Vesicular Disease Virus and Vesicular Stomatitis Virus in an area of livestock units without any control measures and measurement of consequential impact resulting from an assumed introduction into one livestock farm Dr. Dirk Eisinger, Dr. Dirk Eisinger Dr. Dirk EisingerSearch for more papers by this author Dr. Dirk Eisinger, Dr. Dirk Eisinger Dr. Dirk EisingerSearch for more papers by this author First published: 21 May 2012 https://doi.org/10.2903/sp.efsa.2012.EN-285 This external report is not produced by EFSA. It is published to help keep the public informed of developments related to EFSA's scientific work. EFSA reserves its rights, view and position as regards the issues addressed and conclusions reached in the present document, without prejudice to the rights of the authors. Published date: 21 May 2012 Question number: EFSA-Q-2011-01135 AboutPDF ToolsExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinkedInRedditWechat References Backer, J.A., Brouwer, H., van Schaik, G., van Roermind, H.J.W., 2011. Using mortality data for early detection of Classical Swine Fever in The Netherlands. Prev. Vet. Med. 99, 38– 47. Backer, J.A., Hagenaars, T.J., van Roermund, H.J.W., de Jong, M.C.M., 2009. Modelling the effectiveness and risks of vaccination strategies to control classical swine fever epidemics. Journal of the Royal Society Interface 6, 849– 861. Bates, T.W., Thurmond, M.C., Carpenter, T.E., 2003. Description of an epidemic simulation model for use in evaluating strategies to control an outbreak of foot-and-mouth disease. Am. J. Vet. Res. 64, 195– 204. EFSA, 2012. Scientific Opinion on Swine Vesicular Disease and Vesicular Stomatitis. The EFSA Journal 10, 2631. Elbers, A.R.W., Stegeman, A., Moser, H., Ekker, H.M., Smak, J.A., Pluimers, F.H., 1999. The classical swine fever epidemic 1997–1998 in the Netherlands: descriptive epidemiology. Prev. Vet. Med. 42, 157– 184. Garner, M.G., Beckett, S.D., 2005. Modelling the spread of foot-and-mouth disease in Australia. Aust Vet J 83, 758– 766. Grimm, V., Berger, U., Bastiansen, F., Eliassen, S., Ginot, V., Giske, J., Goss-Custard, J., Grand, T., Heinz, S., Huse, G., Huth, A., Jepsen, J.U., Jørgensen, C., Mooij, W.M., Müller, B., Pe'er, G., Piou, C., Railsback, S.F., Robbins, A.M., Robbins, M.M., Rossmanith, E., Rüger, N., Strand, E., Souissi, S., Stillman, R.A., Vabø, R., Visser, U., DeAngelis, D.L., 2006. A standard protocol for describing individual-based and agent-based models. Ecol. Modell. 198, 115– 126. Grimm, V., Berger, U., DeAngelis, D.L., Polhill, J.G., Giske, J., Railsback, S.F., 2010. The ODD protocol: a review and first update. Ecol. Modell. 221, 2760– 2768. Harvey, N., Reeves, A., Schoenbaum, M.A., Zagmutt-Vergara, F.J., Dubé, C., Hill, A.E., Corso, B.A., McNab, W.B., Cartwright, C.I., Salman, M.D., 2007. The North American Animal Disease Spread Model: A simulation model to assist decision making in evaluating animal disease incursions. Prev. Vet. Med. 82, 176– 197. Ribbens, S., Dewulf, J., Koenen, F., Laevens, H., de Kruif, A., 2004. Transmission of classical swine fever. A review. Veterinary Quarterly 26, 146– 155. Staubach, C., Teuffert, J., Thulke, H.-H., 1997. Risk analysis and local spread mechanisms of classical swine fever. Epidémiol. santé anim. 31–32, 6.12.1– 3. Stegeman, A.J., Elbers, A.R.W., Bouma, A., de Jong, M.C.M., 2002. Rate of inter-herd transmission of classical swine fever virus by different types of contact during the 1997–8 epidemic in The Netherlands. Epidemiol. Infect. 128, 285– 291. Thulke, H.-H., Eisinger, D., Beer, M., 2011. The role of movement restrictions and pre-emptive destruction in the emergency control strategy against CSF outbreaks in domestic pigs. Prev. Vet. Med. 99, 28– 37. Volume9, Issue5May 2012285E ReferencesRelatedInformation

Modelling the effectiveness and risks of vaccination strategies to control classical swine fever epidemics

In a recent update of the Dutch contingency plan for controlling outbreaks of classical swine fever (CSF), emergency vaccination is preferred to large-scale pre-emptive culling. This policy change raised two questions: can emergency vaccination be as effective as pre-emptive culling, and what are the implications for showing freedom of infection? Here, we integrate quantitative information available on CSF virus transmission and vaccination effects into a stochastic mathematical model that describes the transmission dynamics at the level of animals, farms and livestock areas. This multilevel approach connects individual-level interventions to large-scale effects. Using this model, we compare the performance of five different control strategies applied to hypothetical CSF epidemics in The Netherlands and, for each of these strategies, we study the properties of three different screening scenarios to show freedom of infection. We find that vaccination in a ring of 2 km radius around a detected infection source is as effective as ring culling in a 1 km radius. Feasible screening scenarios, adapted to the use of emergency vaccination, can reduce the enhanced risks of (initially) undetected farm outbreaks by targeting vaccinated farms. Altogether, our results suggest that emergency vaccination against CSF can be equally effective and safe as pre-emptive culling.

Simulated financial losses of classical swine fever epidemics in the Finnish pig production sector

Rapid structural change and concentration of pig production in regions with most intensive production has raised concerns about whether the risk of large-scale disease losses has increased in Finland. This paper examines the pig industry's losses due to classical swine fever (CSF) epidemics. The work is based on economic and epidemiological models providing insights to the consequences of epidemics to infected and uninfected farms, government and meat processing. The economic analysis was carried out by use of a sector model, which simulated the recovery of pig production, starting from the recognition of the disease in the country and ending at a steady-state market equilibrium about 12 years later. The model explicitly took into account profit-maximising behaviour of producers and the effects of decrease in export demand. Epidemiological evidence suggests that under the current spatially diversified structure of Finnish pig farming and related industries, the probability of a severe disease epidemic counting dozens of infected farms is small. Even for epidemics considered large in Finland (5–33 infected farms) combined with a major reduction in export demand, the median loss was simulated to be only €19.2 million. The majority of these losses were due to loss of exports corresponding almost 20% of pig meat production in Finland. While the current structure of pig farming in Finland incurs higher production costs than the most intensive structures in Europe, it also seems to decrease the probability of ‘catastrophic’ economic losses. The results suggest that the response of export markets and the number of uninfected farms affected by preventive measures are critical to the magnitude of losses, as they can amplify losses even if only few farms become infected.

Evaluation of Measures for the Control of Classical Swine Fever Using a Simulation Model

Abstract. A stochastic and temporal simulation model has been developed to simulate the spread of classical swine fever among herds within a certain area due to farm contacts and local spread. Due to spatial as well as on-farm level heterogeneities in pig production the model allows for the importing of individual farm data. The control measures movement restrictions within protection and surveillance zones, pre-emptive slaughter in proximity to detected farms and animal contact tracing with subsequent culling, applied additionally to stamping-out infected farms, were compared in relation to their effect on the size and the duration of possible epidemics. Additionally, the effects of varying efficiency in contact tracing were analysed. An area with 2986 pig farms and a density of 1.34 farms per km² was generated stochastically for the analysis. When stamping-out infected herds was applied as a single measure, 532 farms became infected on average. The additional application of restriction zones led to a mean epidemic size of 8 infected farms. When all control measures were applied, 5 outbreaks occurred on average. However, the high number of herds depopulated in total curtailed the relative priority of this control strategy. Thus, the presented results point out the necessity to weigh up the advantages and disadvantages in the determination of the optimal control strategy. The simulation model is shown to be a good method to assess the possible consequences of different control measures. The control measures laid down in the EU Council Directive 2001/89/EC (stamping-out infected herds, contact tracing and implementation of restriction zones) seemed to be sufficient for the eradication of classical swine fever epidemics in a region of such farm density. A further reduction in the mean number of outbreaks could be observed when tracing efficiency increased and animal contacts were traced more quickly.

Phylogenetic characterization of classical swine fever viruses isolated in Korea between 1988 and 2003

Twenty-four isolates of classical swine fever (CSF) virus which were obtained from CSF outbreaks during 1988 and 2003 in the Republic of Korea were genetically characterized for partial E2 gene (190 nucleotides) and compared with CSF viruses reported by other countries. Phylogenetic analyses classified Korean field isolates between1988 and 1999 into subgroup 3.2, forming an independent clade distinct from CSF viruses identified in other countries. In contrast, the viruses isolated during 2002–2003 CSF epidemics were classified into a different subgroup (2.1). The 2.1 viruses showed a close genetic relationship (92.1–100% nucleotide similarity) with CSF viruses reported from China and Taiwan in 1998–2001. As no evidence of CSF virus infection was detected in the wild boar ( Sus scrofa coreanus) population that inhabits Korea, the results of molecular characterization strongly suggest that CSF epidemic outbreaks in Korean swine populations during 2002–2003 were attributed to the introduction of a new strain or strains, likely from neighboring countries.

Sensitivity Analysis to Evaluate the Impact of Uncertain Factors in a Scenario Tree Model for Classical Swine Fever Introduction

Introduction of classical swine fever virus (CSFV) is a continuing threat to the pig production sector in the European Union. A scenario tree model was developed to obtain more insight into the main risk factors determining the probability of CSFV introduction (P(CSFV)). As this model contains many uncertain input parameters, sensitivity analysis was used to indicate which of these parameters influence model results most. Group screening combined with the statistical techniques of design of experiments and meta-modeling was applied to detect the most important uncertain input parameters among a total of 257 parameters. The response variable chosen was the annual P(CSFV) into the Netherlands. Only 128 scenario calculations were needed to specify the final meta-model. A consecutive one-at-a-time sensitivity analysis was performed with the main effects of this meta-model to explore their impact on the ranking of risk factors contributing most to the annual P(CSFV). The results indicated that model outcome is most sensitive to the uncertain input parameters concerning the expected number of classical swine fever epidemics in Germany, Belgium, and the United Kingdom and the probability that CSFV survives in an empty livestock truck traveling over a distance of 0-900 km.

Simulated detection of syndromic classical swine fever on a Finnish pig-breeding farm

Although Finland has not experienced a classical swine fever (CSF) epidemic since 1917, the concern about early detection is relevant. The time until detection of CSF on a pig-breeding farm was predicted by simulation, and earlier detection of CSF-infected farms was assessed. Eight to 12 weeks will pass before CSF is detected on a Finnish pig-breeding farm, which resembles detection of the index farm for actual CSF epidemics in Europe. Although notification of suspected CSF on the infected farm accelerates detection the most, interventions aimed at promoting investigations of the general health problem noticed on the farm, or a more comprehensive testing of samples currently arriving from pig farms to the investigating laboratory could shorten detection time by 3 weeks. Results are applicable for further simulation of an event of a CSF epidemic in Finland, and for studying contingency options to promote more rapid detection of infectious diseases of swine not found at present in the country.

Monte Carlo simulation of classical swine fever epidemics and control

A stochastic and spatial simulation model was developed to simulate the spread of classical swine fever virus among herds in a certain area. A model is a simplification of a real system. The mechanisms and parameters are often not exactly known. Validation is necessary to gain insight into model behaviour and to identify risk factors with great impact on the response variables. Several risk factors such as incubation period, number of daily farm contacts, probability of detection, probability of infection after contact, probability of local spread and time from infection to infectivity were considered in the model as probability distributions in order to take the stochastic component of disease dynamics into account. In order to estimate the effects of the risk factors on the response variables mean size and duration of epidemics, a sensitivity analysis was performed. A fractional factorial design with two-level factors (2(7-2) design) was developed to gain the maximum strength with minimum demand on the calculating capacity. The main factors were unconfounded with any other main factor and also unconfounded with two-factor interactions. Apart from the time from infection to infectivity, all risk factors had a significant effect on the mean size and duration of epidemics (p<0.05). Eight two-factor interactions had a significant influence as well (p<0.05). Mainly, two-factor interactions with probability of detection were significant thus emphasising the impact of a rapid detection of outbreaks. The reaction of the simulation responses to changing of the parameter values was consistent with the expected reaction.

Monte Carlo simulation of classical swine fever epidemics and control

A Monte Carlo simulation has been developed to describe the spread of classical swine fever virus between farms within a certain region. The data of the farms can be imported and considered individually. Transmission occurs via the infection routes direct animal and indirect person and vehicle contact, as well as by contaminated sperm and local spread. Parameters, such as incubation period and probability of detection, can be varied by the user and their impact on disease spread can be studied. The control measures stamping-out, movement control and pre-emptive slaughter in circular restriction areas as well as contact tracing can be applied and their effect on disease spread can thus be analysed. The numbers of culled and restricted farms and animals per epidemic and per day within an epidemic, the epidemic duration and the total length of restrictions per restricted farm are given. In an example, simulation runs were performed under the condition of application of all four-control measures. Because no real farm data were available, a test area was generated stochastically with a farm density of 1.3 farms/km(2). The distributions of the number of infected farms per epidemic and the epidemic length are shown.

The effectiveness of classical swine fever surveillance programmes in The Netherlands

Consequences of classical swine fever (CSF) epidemics depend on the control measures, but also on the number of infected herds at the end of the high-risk period (HRP). Surveillance programmes aim to keep this number as low as possible, so the effectiveness of surveillance programmes can be measured by the number of infected herds at the end of the HRP. In this paper, an evaluation of the effectiveness of the following five Dutch CSF surveillance programmes is presented: (1) routine gross pathology of severely diseased pigs; (2) routine virological tests of tonsils of all pigs, submitted under 1; (3) daily clinical observation by the farmer; (4) periodic clinical inspection by a veterinarian; (5) leucocyte counts in blood samples from diseased animals on a herd where antimicrobial ‘group therapy’ is started. The evaluation was done by a modelling study, in which virus transmission, disease development, and actions and diagnostic tests in surveillance programmes were simulated. Also, the yearly costs of the programmes were calculated, and direct costs of CSF epidemics were related to the number of infected herds at the end of the HRP. It appeared that the current Dutch surveillance programmes, without the leucocyte counts, keep the number of infected herds at the end of the HRP below 20 with 95% probability. Leaving out the most-expensive programme of periodic inspection (12.5 M€ per year) does not change this result – indicating that (for CSF surveillance) the programme could well be stopped. If the leucocyte programme, which is currently not effective due to the low sample submission rate, optimally were applied, the 95th percentile could be reduced to 10 infected herds. However, whether application is beneficial is unclear, because of uncertainty of the economic benefits due to the many expected false-positive herds each year.

Quantification of the effect of control strategies on classical swine fever epidemics

Emergency vaccination during an epidemic of classical swine fever virus (CSFV) has become a serious option because of the ethical problems of strategies with massive culling and the availability of a marker vaccine that reduces virus transmission. Here we present a model of between-herd CSFV transmission, which quantifies the effect of control strategies with and without vaccination. We estimate the model parameters from data of the Dutch CSFV epidemic of 1997/1998. With the model, a set of control strategies is compared, consisting of five control measures in several combinations. Consequently, the following general requirements of successful strategies can be formulated. First, to achieve extinction of a CSFV epidemic, transmission through transport should be prevented and the indirect virus transmission, i.e. all transmission not through animal contacts, should at least be halved, either by vaccination or by culling of the susceptible pig population. Second, to minimize the size and duration of an epidemic, the extinction requirements should be met quickly and indirect virus transmission should be reduced by far more than a half. Although the origin of the model parameters let the requirements in fact be only applicable for the south-eastern part of the Netherlands, it is argued that epidemics in other areas will not need stricter control strategies.

Who gains, who loses? Welfare effects of classical swine fever epidemics in the Netherlands

A sectoral market model and a stochastic epidemiological model were used to simulate the effects of classical swine fever (CSF) epidemics in the Netherlands in 1997-1998. Compulsory EU control measures were implemented. Welfare changes of Dutch stakeholders, as well as government costs, were calculated. In a medium-sized epidemic without export restrictions, pig producers' surplus increased by Euro 502 million, but producers within quarantine areas lost. Consumer surplus fell by Euro 552 million. With a ban on live pig exports, pig producers collectively lost whereas consumers gained or experienced only a small loss. Government costs were lower when exports were banned, although net welfare losses were higher. Net welfare losses increased more than proportionately with epidemic size.

Simulated effect of pig-population density on epidemic size and choice of control strategy for classical swine fever epidemics in The Netherlands

We examined the importance of pig-population density in the area of an outbreak of classical swine fever (CSF) for the spread of the infection and the choice of control measures. A spatial, stochastic, dynamic epidemiological simulation model linked to a sector-level market-and-trade model for The Netherlands were used. Outbreaks in sparsely and densely populated areas were compared under four different control strategies and with two alternative trade assumptions. The obligatory control strategy required by current EU legislation was predicted to be enough to eradicate an epidemic starting in an area with sparse pig population. By contrast, additional control measures would be necessary if the outbreak began in an area with high pig density. The economic consequences of using preventive slaughter rather than emergency vaccination as an additional control measure depended strongly on the reactions of trading partners. Reducing the number of animal movements significantly reduced the size and length of epidemics in areas with high pig density. The phenomenon of carrier piglets was included in the model with realistic probabilities of infection by this route, but it made a negligible contribution to the spread of the infection.

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 ≈US$ 9 million. The approach is general and could also be applied to other diseases and countries.