Progress 12/01/04 to 11/30/09
Outputs
OUTPUTS: Over the lifetime of this project, the FMD model which started out modeling FMD in a 3-county region of California has been expanded to work on a statewide and national level. Statewide movement bans, surveillance zones, vaccination and culling have been introduced as modifications to the model to more accurately reflect realistic scenarios likely to be encountered if FMD were to enter the US and to make the model more "user-friendly" by improving the graphic user interface (GUI). The model now runs on a cluster of computers which permits evaluation of extensive amounts of spatially-referenced data. Most recently the model has been validated using data from the 2001 FMD epidemic in the UK and outbreak data from Argentina and eradication strategies have been evaluated. PARTICIPANTS: 1 Principle investigator 1 programmer 2 analysts Assistance in the project was provided by Dr Mark Woolhouse at the UNiversity of Edinburgh and his PhD student Paul Bessel. Additionally data was provided by Miles Thomas of the UK's Department for Environment, Food and Rural Affairs (DEFRA) and Argentina data were provided by Dr Andres Perez of the Center for Animal Disease Modeling and Surveillance (CADMS). TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Work performed over the life of this project has shown that in California, ring vaccination of all animals within a specified distance of an infected herd consistently decreased size and duration of an epidemic. Additionally we identified that our knowledge of animal movements within the 3 county area did not reflect movements on a state level. The present study also found more high risk indirect contacts occurring on beef operations than previously reported. As a result of these differences, epidemic simulation models for California based on earlier data likely under predicted disease transmission patterns involving beef herds. In our work to validate our model using Argentinian outbreak data, we found that all scenarios that start with a single index herd produce outbreaks that are both smaller and shorter than the actual epidemic, in which 65 herds were infected over the course of 70 days. In 100 realizations of Scenario 1 (outbreak in Mar Chiquita alone, Weibull distance kernel), an average of 28 (range: 5 to 97) premises were infected, in outbreaks lasting an average of 27 (range: 19 to 38) days. Outbreaks in Scenario 3 (outbreak in Mar Chiquita and neighboring departments, Weibull distance kernel) were larger, affecting an average of 40 herds over an average of 32 days. It appears that repeated introductions of FMD into Mar Chiquita from neighboring departments may have played an important role in determining the size and duration of the outbreak. We found no significant difference in outbreak size or duration between runs that used Weibull distance kernels and those that modeled transmission as independent of distance. This may be related to the relatively small area that we considered, and certainly implies that local depletion of susceptible premises was not important in slowing the spread of the epidemic. It suggests that the model is not overly sensitive to assumptions made within the model as they relate to the distance of disease transmission. Evaluation of the model using outbreak data from the 2001 UK FMD outbreak looked at fitting different models to data. By doing this we can show that the data are better described by models with density independent disease transmission which is the method of transmission used by our model for indrect contact transmission. Previous models that were used to evaluate control strategies in the UK assumed density dependent disease transmission. Our results therefore suggest that the effect of pre-emptive culling on disease control has been overestimated by previous models. A manuscript detailing our findings is being written.
Publications
- No publications reported this period
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Progress 12/01/07 to 11/30/08
Outputs
OUTPUTS: Median number of interstate (movements both into and out of California) animal movements was found to be 0.17 per month, or more than twice per year. Total median monthly animal movements were 1.44 from the respondents' premises for all herd sizes and 0.54 for beef herds <250 head and 0.36 for beef herds ≥250 head to the respondents' premises. Respondents kept beef cattle at up to 5 locations throughout the year. More than 40% of the movements from the respondents' premises were to a salesyard or auction. Duration, number of infected premises and culled animals, and spatial distribution of infected herds, resulting from the simulated outbreaks, varied considerably among geographic regions, depending on index case type and location. Outbreaks beginning in the south region of California were consistently longest, while those beginning in the north region were shortest. The largest outbreaks resulted from index cases located in the south and valley regions, while outbreaks were the smallest when originating in the Sonoma or north regions. For all regions, when the index herd was a dairy, size and duration of the outbreak were consistently reduced with implementation of a 3-day or longer statewide movement ban (SWMB). PARTICIPANTS: Nothing significant to report during this reporting period. TARGET AUDIENCES: Nothing significant to report during this reporting period. PROJECT MODIFICATIONS: Nothing significant to report during this reporting period.
Impacts
Frequency of animal movements in this statewide study differed from previously-reported values for monthly shipments of animals to and from beef operations in three counties of California. The present study found more frequent movements of animals to and from beef operations of all sizes. In addition, the present study also found more high risk indirect contacts occurring on beef operations than previously reported. However, the number of low risk indirect contacts reported here were similar for small beef operations but less for large beef operations than reported previously. As a result of these differences, epidemic simulation models for California based on earlier data likely under predicted disease transmission patterns involving beef herds. Results show that following the introduction of FMDV from wild pigs into a dairy or beef herd, it could result in a large and rapidly spreading outbreak, potentially affecting large numbers of herds. The size and duration of the outbreak can be reduced with an SWMB; however, the impact is highly dependent on the index herd type and location.
Publications
- Mario Pineda-Krch, Joshua M. O' Brien, Clair Thunes, Tim E Carpenter, 2009. Potential impact of an introduction of foot-and-mouth disease from wild pigs into commercial livestock premises in California, American Journal of Veterinary Research (in press).
- Edith S. Marshall, Tim E Carpenter, Clair Thunes, 2009. Cattle movements and other contact rates among beef herds in California, with reference to the potential spread and control of foot-and-mouth disease (in press).
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Progress 12/01/06 to 11/30/07
Outputs
OUTPUTS: In 2005 a paper survey of livestock producers in California was performed. Approximately 5500 surveys were mailed out with assistance from state level livestock associations, with the mean response rate of approximately 30%. The data collected have allowed direct and indirect parameters to be calculated for this larger geographic area and the model has been expanded to run for the state of California. Information gathered regarding movements of animals has resulted in a new shipping distance parameter. In addition an online survey was released nationally in 2006 to gather similar data on a national level. Responses are still being collected and the model has been scaled up to run on the national level. Currently the model is parameterized with the data collected in California; however, once the national data have been analyzed these will be used to make changes as necessary to model parameters. In 2007 a graphic user interface (GUI) was created for the model which allows
non-programmers to run scenarios for various states. Simulation runs performed in California have looked at various scenarios including the use of alternative ring vaccination strategies, use of movement controls, the importance of knowing accurate livestock facility locations, and resource constraints for example limited amounts of vaccine. The model now runs on a 20-node computer cluster and measures were taken to increase the speed with which simulations run. As a result the model can run at the state and national levels. Presentation given within this period follow; Presentation (T. Carpenter) - "Distillation of Simulation Scenario Results", Council of Research Workers on Animal Diseases (CRWAD), Chicago, IL, Dec 4-5, 2006. Invited Presentation (T. Carpenter) - "Foreign Animal Disease Modeling", University of California, Davis; UC Davis Goat Day Meeting, Jan 20, 2007. Invited Presentation (T. Carpenter) - "Multicenter comparison of modelling tools for the evaluation of foot and
mouth disease vaccination strategies in Denmark", Foreign Animal Disease Modeling Meeting, Arlington, VA, Aug 22, 2007. Invited Speaker (C. Thunes) - National Institute of Animal Agriculture ID Expo, Kansas City, MO, Aug 27 - 30, 2007, Invited Presentation (T. Carpenter) - "Analisis de Riesgo y sus Aplicaciones Conceptos teoricos y algunos ejemplos", Ministry of Agriculture, Madrid, Spain, Sept 2007. Invited Presentation (T. Carpenter) - "Modelos de Simulacion: Conceptos teoricos y algunos ejemplos", Faculty of Veterinary Medicine, Madrid, Spain, Sept 20, 2007. Invited Presentation (T. Carpenter) - "Modeling as a tool for surveillance planning and analysis", US Animal Health Association Meeting, Reno, NV, Oct 21, 2007. Invited Presentation (T. Carpenter) - "FMD modeling: linking epidemiology and economics to aid decision making", Department of Homeland Security, Washington, DC, Nov 10, 2007. Invited Presentation (T. Carpenter) - "Epidemiologic model of foot-and-mouth disease: moving
from premises to a national model", 2007 TAMU Symposium on Geospatial Technologies and Public Health: mapping disease, promoting health, College Station, TX, Nov 17, 2007.
PROJECT MODIFICATIONS: In the original proposal, we requested funding to validate our model using data collected from the 2001 UK FMD outbreak. We identified Drs. Mark Woolhouse and John Wilesmith as collaborators who would assist in this effort. While we are currently working with Dr. Woolhouse, Dr. Wilesmith has been unable to participate as planned. Because of this, Peter Johnson the National Program Leader has agreed to our expanding the model validation portion of the proposal. We will be performing a similar model validation exercise using data collected from the 2001 FMD outbreak in Argentina.
Impacts
The model provided a means of assessing the relative merits of potential strategies for control and eradication of FMD should it enter the US livestock population. For California, ring vaccination of all animals within a specified distance of an infected herd consistently decreased size and duration of an epidemic. However, constraints on the amount of vaccine available in the face of an outbreak were identified, indicating vaccine should be preferentially administered to dairy animals. Ring vaccination with highly efficacious (90%) vaccine may be the most economically effective strategy to control FMD. Although, less optimal than vaccination, a strategy to slaughter selectively the highest-risk herds was found to be preferable to other preemptive slaughter strategies considered.
Publications
- Marshall, E.M., Carpenter, T.E, and Thurmond, M.C. 2007. Results of a survey of owners of miniature swine to characterize husbandry practices affecting risks of foreign animal disease. JAVMA. 230, 702-707. Thunes, C., and Carpenter, T.E., . 2007. Biosecurity practices and travel history of individuals exhibiting livestock at the 2005 California State Fair. JAVMA. 231, 581-585. Carpenter, T.E, Christiansen L.E, Dickey B.F., Thunes C., and Hullinger P. 2007. The Potential Impact of an Introduction of Foot-and-Mouth Disease into the California State Fair. JAVMA. 231, 1231-1235 Kobayashi M., B.F. Dickey, T.E. Carpenter, and R.E. Howitt. 2007. A dynamic optimal disease control model for foot-and-mouth disease. I. Model description, Preventive Veterinary Medicine.2007. A dynamic optimal disease control model for foot-and-mouth disease. II. Model results and policy implications, Preventive Veterinary Medicine. Dickey, B.F., T.E. Carpenter and S.M. Bartell. 2007. Parsimony in
spatial simulation modeling of
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