North American Animal Disease Spread Research Articles

Simulating the Spread of Peste des Petits Ruminants in Kazakhstan Using the North American Animal Disease Spread Model

In this study, we simulated the potential spread of Peste des Petits Ruminants (PPR) between small ruminant (SR) farms in the Republic of Kazakhstan (RK) in case of the disease’s introduction into the country. The simulation was based on actual data on the location and population of SR farms in the RK using the North American Animal Disease Spread Model (NAADSM). The NAADSM employs the stochastic simulations of the between-farm disease spread predicated on the SIR compartmental epidemic model. The most important epidemiological indicators of PPR, demography of SR farms, and livestock management characteristics in the RK were used for model parameterization. This article considers several scenarios for the initial introduction of PPR into the territory of Kazakhstan, based on previously identified high-risk regions and varying sizes of initially infected farms. It is demonstrated that the duration and size of the outbreak do not depend on the size of initially infected farms but rather depend on the livestock concentration and number of farms in the affected area. This implies that the outbreak may affect the largest number of farms in the case of introduction of the disease into farms in southern Kazakhstan. However, even in the most unfavorable scenario, the total number of affected farms does not exceed 2.4% of all SR farms in the RK. The size of the affected area is, in most cases, no larger than an averaged 2-level administrative division’s size, which suggests the scale of a local epidemic. The chosen model provides ample opportunity to study the impact of different control and prevention measures on the spread of PPR as well as to assess the potential economic damage.

Modeling the Spread of Porcine Reproductive and Respiratory Syndrome Among Pig Farms in Lira District of Northern Uganda.

Porcine Reproductive and Respiratory Syndrome (PRRS) is a viral swine disease that causes reproductive failure in breeding sows and respiratory distress in growing pigs. The main objectives were to simulate the transmission patterns of PRRS in Uganda using North American Animal Disease Spread Model (NAADSM) and to evaluate the potential effect of prevention and control options such as vaccination and movement control. The median number of infectious farms at the end of 52 weeks for the baseline scenario was 735 (36.75% of the 2,000 farms). The best effects of vaccination were observed in scenarios 60% farm coverage and 80% farm coverage, which resulted in 82 and 98.2% reduction in the median number of infectious farms at the end of the simulation, respectively. Vaccination of all medium and large farms only (33% of the farms) resulted in a 71.2% decrease in the median number of infectious farms at the end of 52 weeks. Movement control (MC) results showed that the median number of infectious farms at the end of 52 weeks decreased by 21.6, 52.3, 79.4, and 92.4% for scenarios MC 20, MC 40, MC 60, and MC 80%, respectively. This study provides new insights to the government of Uganda on how PRRS can be controlled. The large and medium farms need to be prioritized for vaccination, which would be a feasible and effective way to limit the spread of PRRS in Uganda. Scavenging pigs should be confined at all times, whether in the presence or absence of any disease outbreaks.

A stochastic simulation model of African swine fever transmission in domestic pig farms in the Red River Delta region in Vietnam.

The main objectives of this study were to model various scenarios of African swine fever (ASF) virus transmission among farms in Vietnam and to evaluate the impact of control strategies using North American Animal Disease Spread Model (NAADSM). A total of 7,882 pig farms in the Red River Delta (RRD) region were obtained from the General Statistics Office, and then, random points corresponding to the number of farms in each province were generated as exact farm locations were not available. A total of 10 models were developed, including movement control scenarios. In addition, we conducted sensitivity analysis to assess the impact of indirect contact transmission probability (TP). Overall, the indirect contact exhibited an important role in transmitting the ASF virus. In order to minimize ASF transmission between farms, we found that movement restriction needed to reach a certain level (approximately between 50% and 75%) and that the restriction had to be applied in a timely manner. This study offers valuable insight into how ASF virus can be transmitted via direct and indirect contact and controlled among farms under the various simulation scenarios. Our results suggest that the enforcement of movement restriction was an effective control measure as soon as the outbreaks were reported. In addition, this study provided evidence that high standards of biosecurity can contribute to the reduction of disease spread.

Movement Restriction and Increased Surveillance as Efficient Measures to Control the Spread of Highly Pathogenic Avian Influenza in Backyard Productive Systems in Central Chile.

During the last 5 years there has been an alarming number of reports of highly pathogenic avian influenza worldwide. However, little is known about the status of this disease in South America. Chile has been the only country in South America where an HPAI outbreak was reported. This outbreak occurred in 2002 and was due to an H7N3 HPAI, where the most plausible hypothesis that explained the entrance of the disease to the country, had relation to migratory wild birds. Commercial poultry farms in Chile are highly integrated and have high biosecurity standards. Nevertheless, poultry backyard production systems lack biosecurity measures and are widely distributed. Since 2002 outbreak, avian influenza viruses have been identified in wild birds and different animal species kept in backyard productive systems (BPS) in Chile. The aim of this study was to simulate the possible natural history of HPAI after its introduction to BPS in central Chile and to simulate different intervention strategies. To do so, the North American Animal Disease Spread Model version 3.3 was used. The results showed that a median of 15,930 BPS would be affected if HPAI spread among BPS in central Chile, representing 97.8% of the current amount of BPS existing in study zone. Movement restrictions, pre-emptive destruction, passive surveillance, tracing of infected premises and combinations of the three, where the intervention strategies tested in the simulation model. From all the interventions simulated, movement restrictions together with increasing surveillance (through increasing passive surveillance and good tracing of infected premises) had the biggest effect, reducing the median number of infected BPS in 90.8%. However, more studies are needed to more accurately estimate local contact rates. These results can guide the official veterinary services to consider potential mechanisms to control or prevent an HPAI emergency situation.

Simulation of control scenarios of porcine reproductive and respiratory syndrome in Nghe An Province in Vietnam

The main objective of this study was to develop various models using North American Animal Disease Spread Model (NAADSM) to simulate the transmission of Porcine reproductive and respiratory syndrome (PRRS) virus between farms in Nghe An Province in Vietnam in order to inform the prevention and control of this important disease. Using real data from the household survey, credible parameters for direct/indirect mean contact rates between different farms were estimated. A total of eleven models were developed, including immunization scenarios. In addition, we conducted sensitive analysis on how the mean contact rates influenced the results. The immunization scenarios showed that a high proportion of pigs in medium size farms needs to be vaccinated in order to reduce the transmission to pigs in small farms under the Vietnamese pig production system. In order to promote the use of vaccinations, incentives (such as a vaccine subsidy) for medium size farms may be needed. It could be the most cost‐effective control and prevention strategy for pig diseases in Vietnam. Our study provides insights on how pig diseases can be spread between pig farms via direct and indirect contact in Nghe An under the various hypothetical scenarios. Our results suggest that medium/large farms may play an important role in the transmission of pig diseases.

BENEFITS OF AN ANIMAL TRACEABILITY SYSTEM FOR A FOOT-AND-MOUTH DISEASE OUTBREAK: A SUPPLY-DRIVEN SOCIAL ACCOUNTING MATRIX APPROACH

AbstractThis study reports the findings for an analysis using the computer program NAADSM (North American Animal Disease Spread Model) and a supply-driven social accounting matrix to examine the impact of a hypothetical foot-and-mouth disease (FMD) outbreak in a relatively isolated part of the United States, Utah, under various levels of livestock traceability. The analysis demonstrates that a significant regional economic impact in Utah would result from an FMD outbreak but that improved levels of traceability would be very important in helping to reduce the negative economic consequences of the outbreak.

Assessment of Effectiveness of Control Strategies Against Simulated Outbreaks of Highly Pathogenic Avian Influenza in Ontario, Canada.

The North American Animal Disease Spread Model (NAADSM) is a stochastic model framework developed to simulate the spread of highly contagious diseases of livestock and poultry, such as foot-and-mouth disease and highly pathogenic avian influenza (HPAI). The objective of this study was to make recommendations on the most effective HPAI control policy for Canada, specifically, on the effect of different speeds of detection, effectiveness of movement restrictions and stamping-out and ring-culling strategies on the magnitude of an HPAI outbreak. In addition, the effect of introduction of infection in a range of multiple farms simultaneously was also evaluated. A total of 21060 scenarios, defined as different combinations of parameters for various epidemiological conditions and control measures, were created to simulate the number of poultry flocks that would become infected as a result of an incursion of HPAI. Each scenario was parameterized in NAADSM and replicated 1000 times, generating the median number of flocks infected at the end of the simulated outbreak for each scenario. Negative binomial regression analysis was used to model significant explanatory variables of the median number of flocks infected at the end of each simulated outbreak for each of the 21060 scenarios. The final model included the following explanatory variables: number and type initially infected flock(s), density of flocks within the county where the initially infected flock(s) was located, probability of transmission through indirect contact, subclinical spread of the infection, speed of detection and a two-way interaction between intensity of bird destruction strategy and movement restriction effectiveness to reduce transmission through direct and indirect contacts. The modelling results suggested that stamping out of the detected infected flocks, without ring culling, in combination with effective movement restrictions on direct and indirect contacts, would be the most appropriate policy for Ontario.

Emergency vaccination use in a modelled foot and mouth disease outbreak in Minnesota.

Epidemiological modelling is an important approach used by the Veterinary Services of the United States Department of Agriculture Animal and Plant Health Inspection Service to evaluate the potential effectiveness of different strategies for handling foot and mouth disease (FMD). Identifying the potential spread of FMD by modelling an outbreak, and then considering the impacts of FMD vaccination, is important in helping to inform decision-makers about the potential outcomes of vaccination programmes. The objective of this study was to evaluate emergency vaccination control strategies used in a simulated FMD outbreak in Minnesota. The North American Animal Disease Spread Model (NAADSM, Version 3.2.18) was used to simulate the outbreak. Large-scale (1,500 herds per day) emergency vaccination reduced the size of the modelled outbreak in both swine and dairy production types, but the effect was larger when the outbreak began in a dairy herd. Large-scale vaccination also overcame limitations caused by delays in vaccine delivery. Thus, even if vaccination did not begin until 21 days into the outbreak, large-scale vaccination still reduced the size and duration of the outbreak. The quantity of vaccine used was markedly larger when large-scale vaccination was used, compared with small-scale (50 herds per day) vaccine administration. In addition, the number of animals and herds vaccinated in an outbreak originating in a herd of swine was substantially lower than in an outbreak beginning in a herd of dairy cattle.

Simulation of between-farm transmission of porcine reproductive and respiratory syndrome virus in Ontario, Canada using the North American Animal Disease Spread Model

Porcine reproductive and respiratory syndrome (PRRS), a viral disease of swine, has major economic impacts on the swine industry. The North American Animal Disease Spread Model (NAADSM) is a spatial, stochastic, farm level state-transition modeling framework originally developed to simulate highly contagious and foreign livestock diseases. The objectives of this study were to develop a model to simulate between-farm spread of a homologous strain of PRRS virus in Ontario swine farms via direct (animal movement) and indirect (sharing of trucks between farms) contacts using the NAADSM and to compare the patterns and extent of outbreak under different simulated conditions. A total of 2552 swine farms in Ontario province were allocated to each census division of Ontario and geo-locations of the farms were randomly generated within the agriculture land of each Census Division. Contact rates among different production types were obtained using pig movement information from four regions in Canada. A total of 24 scenarios were developed involving various direct (movement of infected animals) and indirect (pig transportation trucks) contact parameters in combination with alternating the production type of the farm in which the infection was seeded. Outbreaks were simulated for one year with 1000 replications. The median number of farms infected, proportion of farms with multiple outbreaks and time to reach the peak epidemic were used to compare the size, progression and extent of outbreaks. Scenarios involving spread only by direct contact between farms resulted in outbreaks where the median percentage of infected farms ranged from 31.5 to 37% of all farms. In scenarios with both direct and indirect contact, the median percentage of infected farms increased to a range from 41.6 to 48.6%. Furthermore, scenarios with both direct and indirect contact resulted in a 44% increase in median epidemic size when compared to the direct contact scenarios. Incorporation of both animal movements and the sharing of trucks within the model indicated that the effect of direct and indirect contact may be nonlinear on outbreak progression. The increase of 44% in epidemic size when indirect contact, via sharing of trucks, was incorporated into the model highlights the importance of proper biosecurity measures in preventing transmission of the PRRS virus. Simulation of between-farm spread of the PRRS virus in swine farms has highlighted the relative importance of direct and indirect contact and provides important insights regarding the possible patterns and extent of spread of the PRRS virus in a completely susceptible population with herd demographics similar to those found in Ontario, Canada.

Modeling the impact of vaccination control strategies on a foot and mouth disease outbreak in the Central United States

The central United States (U.S.) has a large livestock population including cattle, swine, sheep and goats. Simulation models were developed to assess the impact of livestock herd types and vaccination on foot and mouth disease (FMD) outbreaks using the North American Animal Disease Spread Model. In this study, potential FMD virus outbreaks in the central region of the U.S. were simulated to compare different vaccination strategies to a depopulation only scenario. Based on data from the U.S. Department of Agriculture National Agricultural Statistics Service, a simulated population of 151,620 livestock operations characterized by latitude and longitude, production type, and herd size was generated. For the simulations, a single 17,000 head feedlot was selected as the initial latently infected herd in an otherwise susceptible population. Direct and indirect contact rates between herds were based on survey data of livestock producers in Kansas and Colorado. Control methods included ring vaccination around infected herds. Feedlots ≥3000 head were either the only production type that was vaccinated or were assigned the highest vaccination priority. Simulated vaccination scenarios included low and high vaccine capacity, vaccination zones of 10km or 50km around detected infected premises, and vaccination trigger of 10 or 100 detected infected herds. Probability of transmission following indirect contact, movement controls and contact rate parameters were considered uncertain and so were the subjects of sensitivity analysis. All vaccination scenarios decreased number of herds depopulated but not all decreased outbreak duration. Increased size of the vaccination zone during an outbreak decreased the length of the outbreak and number of herds destroyed. Increased size of the vaccination zone primarily resulted in vaccinating feedlots ≥3000 head across a larger area. Increasing the vaccination capacity had a smaller impact on the outbreak and may not be feasible if vaccine production and delivery is limited. The ability to vaccinate all the production types surrounding an infected herd did not appear as beneficial as priority vaccination of feedlot production types that have high numbers of indirect contacts. Outbreak duration, number of herds depopulated and the effectiveness of vaccination were sensitive to indirect contact transmission probability and movement restrictions. The results of this study will provide information about the impacts of disease control protocols which may be useful in choosing the optimal control methods to meet the goals of rapid effective control and eradication.

One-Health Simulation Modelling: A Case Study of Influenza Spread between Human and Swine Populations usingNAADSM

The circulation of zoonotic influenza A viruses including pH1N1 2009 and H5N1 continue to present a constant threat to animal and human populations. Recently, an H3N2 variant spread from pigs to humans and between humans in limited numbers. Accordingly, this research investigated a range of scenarios of the transmission dynamics of pH1N1 2009 virus at the swine-human interface while accounting for different percentages of swine workers initially immune. Furthermore, the feasibility of using NAADSM (North American Animal Disease Spread Model) applied as a one-health simulation model was assessed. The study population included 488 swine herds and 29, 707 households of people within a county in Ontario, Canada. Households were categorized as follows: (i) rural households with swine workers, (ii) rural households without swine workers, and (iii) urban households without swine workers. Forty-eight scenarios were investigated, based on the combination of six scenarios around the transmissibility of the virus at the interface and four vaccination coverage levels of swine workers (0-60%), all under two settings of either swine or human origin of the virus. Outcomes were assessed in terms of stochastic 'die-out' fraction, size and time to peak epidemic day, overall size and duration of the outbreaks. The modelled outcomes indicated that minimizing influenza transmissibility at the interface and targeted vaccination of swine workers had significant beneficial effects. Our results indicate that NAADSM can be used as a framework to model the spread and control of contagious zoonotic diseases among animal and human populations, under certain simplifying assumptions. Further evaluation of the model is required. In addition to these specific findings, this study serves as a benchmark that can provide useful input to a future one-health influenza modelling studies. Some pertinent information gaps were also identified. Enhanced surveillance and the collection of high-quality information for more accurate parameterization of such models are encouraged.

Impact of uncertainty in foot and mouth disease indirect transmission probability on outbreak duration and number of herds depopulated

The central United States (US) has a large livestock population including cattle, swine, sheep, and goats that are susceptible to foot and mouth disease (FMD). Because FMD is a highly infective foreign animal disease, the only method to assess the impact of an introduction and the effectiveness of control programs is via modeling. We developed simulation scenarios to assess the impact of the introduction of FMD in the central US and the effect of vaccination strategies and variation in biosecurity on FMD outbreaks using the North American Animal Disease Spread Model (NAADSM), a spatially explicit, stochastic infectious disease model.

Impact of livestock production type vaccination priority order on the control of a foot and mouth disease outbreak in the central United States

The central United States (US) has a large livestock population including cattle, swine, sheep, and goats that are fully susceptible to foot and mouth disease (FMD). Introduction of FMD to the US would have potentially devastating consequences to the livestock industry. Identification of optimal control measures including potential vaccination strategies is essential to minimize the impact of a FMD outbreak. Both dairy and large feedlot operations have frequent indirect contacts, which make them key production types for FMD transmission and thus should be the focus of control strategies. To address this issue, we developed simulation scenarios to assess the impact of livestock production type vaccination priority on FMD outbreaks using the North American Animal Disease Spread Model (NAADSM), a spatially explicit, stochastic infectious disease model.

Evaluation of Strategies for the Eradication of Pseudorabies Virus (Aujeszky's Disease) in Commercial Swine Farms in Chiang-Mai and Lampoon Provinces, Thailand, Using a Simulation Disease Spread Model

Several strategies for eradicating Pseudorabies virus (Aujeszky's disease) in Chiang-Mai and Lampoon Provinces, Thailand, were compared using a computer simulation model, the North American Animal Disease Spread Model (NAADSM). The duration of the outbreak, the number of affected herds and the number of destroyed herds were compared during these simulated outbreaks. Depopulation, zoning for restricted movement and improved detection and vaccination strategies were assessed. The most effective strategies to eradicate Pseudorabies as per the findings from this study are applying depopulation strategies with MOVEMENT RESTRICTIONS in 3-, 8- and 16-km ZONES surrounding infected herds and enhancing the eradication with vaccination campaign on 16-km radius surrounding infected herds.

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

Foot and mouth disease model verification and ‘relative validation’ through a formal model comparison

Researchers from Australia, New Zealand, Canada and the United States collaborated to validate their foot and mouth disease models--AusSpread, InterSpread Plus and the North American Animal Disease Spread Model--in an effort to build confidence in their use as decision-support tools. The final stage of this project involved using the three models to simulate a number of disease outbreak scenarios, with data from the Republic of Ireland. The scenarios included an uncontrolled epidemic, and epidemics managed by combinations of stamping out and vaccination. The predicted numbers of infected premises, the duration of each epidemic, and the size of predicted outbreak areas were compared. Relative within-model between-scenario changes resulting from different control strategies or resource constraints in different scenarios were quantified and compared. Although there were differences between the models in absolute outcomes, between-scenario comparisons within each model were similar. In all three models, early use of ring vaccination resulted in the largest drop in number of infected premises compared with the standard stamping-out regimen. This consistency implies that the assumptions made by each of the three modelling teams were appropriate, which in turn serves to increase end-user confidence in predictions made by these models.

The North American Animal Disease Spread Model: A simulation model to assist decision making in evaluating animal disease incursions

The North American Animal Disease Spread Model is a stochastic, spatial, state-transition simulation model for the spread of highly contagious diseases of animals. It was developed with broad international support to assist policy development and decision making involving disease incursions. User-established parameters define model behavior in terms of disease progression; disease spread by animal-to-animal contact, contact with contaminated personnel or equipment, and airborne dissemination; and the implementation of control measures such as destruction and vaccination. Resources available to implement disease control strategies, as well as the direct costs associated with these strategies, are taken into consideration. The model records a wide variety of measures of the extent of simulated outbreaks and other characteristics. The graphical interface and output visualization features also make it a useful tool for training and preparedness exercises. This model is now being used to evaluate outbreak scenarios and potential control strategies for several economically important exotic animal diseases in the United States, Canada, and elsewhere. NAADSM is freely available via the Internet at http://www.naadsm.org.