ABSTRACT
Foot and Mouth disease (FMD) is a highly contagious viral disease that affects all cloven-hoofed animals. Because of its devastating effects on the agricultural industry, many countries take measures to stop the introduction of FMD virus into their countries. Decision makers at multiple levels of the United States Department of Agriculture (USDA) use Risk Assessments (RAs) (both quantitative and qualitative) to make better and more informed scientifically based decisions to prevent the accidental or intentional introduction of the disease. There is a need for a generic RA that can be applied to any country (whether FMD free or non-FMD free) and for any product (FMD infected animals and animal products). We developed a user-friendly generic RA tool (software) that can be used to conduct and examine different scenarios of quantitative/qualitative risk assessments for the different countries with their varying FMD statuses in relation to reintroduction of FMD virus into the USA. The program was written in Microsoft Visual Basic 6.0 (Microsoft Corporation, Redmond, Washington, USA). The @Risk 6.1 Developer Kit (RDK) and @Risk 6.1 Best Fit Kit library (Palisade Corporation, Newfield, NY.USA) was used to build Monte Carlo simulation models. Microsoft Access 2000 (Microsoft Corporation, Redmond, Washington, USA) was used and SQL to query the data. Different input probability distributions can be selected for the nodes in the scenario tree and different output for each end-state of the simulation is given in different graphical formats and statistical values are used in describing the likelihood of FMD virus introduction. Sensitivity Analysis in determining which input factor has more effect on the total risk outputs is also given. The developed generic RA tools can be eventually extended and modified to conduct RAs for other animal diseases and animal products.
ABSTRACT
Computational models, such as in epidemiology, provide a powerful tool that can be used to systematically examine an array of dynamic interactions among populations as well as to evaluate altemate disease intervention strategies. The specific objectives in this study were to: a/ examine the interaction of cellular (CD4) and HIV population dynamics and evaluate the impact of the use of combination chemotherapies on viral and CD4 populations (Experiment #1), b/ demonstrate how modelling can be used to evaluate the impact of an intervention (condom use) on reducing the rate of HIV/AIDS (Experiment #2). In this study, we used state transition models and conducted simulation experiments to evaluate various alternatives for the control and/or prevention of HIV/AIDS. The result indicated that combination therapy (double or triple drug therapies) was very effective. The HIV viral population decreased rapidly and remained suppressed for years. On the other hand, the CD4 cell population increased above 400 cells per ml and was maintained above that level for many years. Mono-therapy was not as effective; although the viral load decreased rapidly, it increased to its original levels within a few months. Since condom use is one of the key interventions of HIV/AIDS, we evaluated its use in 25%, 50% and 75% of an adult, sexually active population. Increasing condom use by 50% and 75% above an estimated baseline of 25% reduced the incidence of AIDS by 53% in Blacks, 49% in Hispanics and 43% in Whites. The study shows how a cellular/molecular level model can be incorporated within a macro-epidemiologic systems dynamics model to evaluate a variety of scientific questions such as to see if cellular/molecular level interventions reduce morbidity and mortality rates in HIV.
