Cooperative Ecosystem Studies Unit, Rocky Mountain CESU

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The U.S. Geological Survey¿s (USGS) National Wildlife Health Center is offering a funding opportunity to a CESU partner having demonstrated capability in spatial statistics and spatial-temporal statistical modeling of wildlife diseases. Disease mitigation tactics for wildlife are limited, and vaccination is one tool that holds promise for reducing the effects of disease on wildlife. We have developed spatially-explicit models parameterized from lab and field trials of an oral sylvatic plague vaccine (SPV), that allow us to explore the effects of vaccination and other plague mitigation tactics, as well as local environmental conditions on plague transmission dynamics. These models will provide important information for management agencies implementing plague control programs under increasingly erratic weather conditions. This opportunity is to evaluate different vaccination strategies for SPV, and address question such as what percentage of prairie dogs in a colony are required to be vaccinated in order for a population to survive under persistent pressure from plague. Can vaccination firewalls be built surrounding infected prairie dog towns and successfully prevent the spread of plague? Are small colonies less likely to benefit from the effect of SPV? Does dusting with insecticides play a role in designing the optimal strategy for plague management? What are the predicted long-term effects of a vaccination strategy on small mammal communities? How will optimal strategies change under drought conditions? USGS have developed a spatially-explict model of prairie dog and flea dynamics that includes options for including plague in the system. This model incorporates data from the SPV field trials, and laboratory trials at NWHC. Prairie dogs proceed from susceptible to infected by encountering other infected prairie dogs, being bitten by infected fleas, or encountering a carcass that has suffered plague mortality. These encounters occur based on multinomial probabilities parameterized from field and lab data. The model includes fleas in 4 stages of plague exposure include susceptible, early phase, latent phase, and late phase, which allows us to explore hypothesis regarding the role of early phase versus late phase transmission of plague from fleas to prairie dogs (currently in debate in the literature see Lorange et al. 2005, Eisen et al., 2006). Currently USGS is exploring the sensitivity of the models due to parameter uncertainty. These models include a parameter to indicate whether a prairie dog is susceptible or not to plague based on whether the prairie dog consumed a vaccine-laden bait (based on field trials) and the estimated probability the vaccine is effective (based on lab trials). In addition, reproduction and mortality of fleas can be linked to climate variables such as temperature and humidity to provide predictions regarding the effects of climate change on plague transmission.

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