Simulating sterilization, vaccination, and test-and-remove as brucellosis control measures in bison

Ebinger, Mike; Cross, Paul; Wallen, Rick; White, Patrick; Treanor, John

Brucella abortus, the causative agent of bovine brucellosis, infects wildlife,cattle, and humans worldwide, but management of the disease is often hindered by the logisticsof controlling its prevalence in wildlife reservoirs. We used an individually basedepidemiological model to assess the relative efficacies of three management interventions(sterilization, vaccination, and test-and-remove). The model was parameterized withdemographic and epidemiological data from bison in Yellowstone National Park, USA.Sterilization and test-and-remove were most successful at reducing seroprevalence when theywere targeted at young seropositive animals, which are the most likely age and sex category tobe infectious. However, these approaches also required the most effort to implement.Vaccination was less effective (even with a perfect vaccine) but also required less effort toimplement. For the treatment efforts we explored (50–100 individuals per year or 2.5–5% ofthe female population), sterilization had little impact upon the bison population growth ratewhen selectively applied. The population growth rate usually increased by year 25 due to thereduced number of Brucella-induced abortions. Initial declines in seroprevalence followed byrapid increases (.15% increase in 5 years) occurred in 3–13% of simulations with sterilizationand test-and-remove, but not vaccination. We believe this is due to the interaction ofsuperspreading events and the loss of herd immunity in the later stages of control efforts asdisease prevalence declines. Sterilization provided a mechanism for achieving large diseasereductions while simultaneously limiting population growth, which may be advantageous insome management scenarios. However, the field effort required to find the small segment ofthe population that is infectious rather than susceptible or recovered will likely limit the utilityof this approach in many free-ranging wildlife populations. Nevertheless, we encouragescientists and policy makers to consider sterilization as part of a suite of available brucellosismanagement tools.

Simulating sterilization, vaccination, and test-and-remove as brucellosis control measures in bison

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