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.

Evaluation of the fluorescence polarization assay for the detection of Brucella abortus antibodies in bison in a natural setting.

Bison and elk in the greater Yellowstone area are the last-known reservoir of Brucella abortus in the United States. Diagnosis of brucellosis is challenging as there is no perfect reference test. The objectives of this study were to estimate the accuracy of the fluorescence polarization assay (FPA) for the screening of B. abortus antibodies in bison in a natural setting. Serum and tissue samples were collected and analyzed from the known brucellosis-infected bison herd in Yellowstone National Park (YNP). Additionally, serum samples from privately owned bison were serologically tested for brucellosis. While the FPA and five other tests had perfect sensitivity, all tests had substantially lower specificity in the YNP herd. However, a Bayesian analysis showed that as many as 59-74% of the culture-negative animals were most-likely truly infected. A decision-tree analysis showed that the expected cost of FPA testing was comparable to the cost of other serologic tests. The FPA was shown to be highly sensitive but may not be able to differentiate culture-positive and culture-negative animals. There is a need for long-term longitudinal studies to estimate diagnostic accuracy of tests for B. abortus in bison.