Sylvatic plague, a zoonotic flea-borne disease, caused by the bacterium Yersinia pestis, is relevant to Department of Defense (DOD) as prairie dogs and other susceptible rodents are present on military installations in several western states. Arthropod-borne diseases, like plague, are thought to be particularly sensitive to local climate conditions. Expected changes in temperature and humidity over the next several decades will likely increase the geographical expansion of plague outbreaks in wildlife. Through a combination of field and laboratory work, along with data-driven modeling, the project team evaluated the potential effects of climate change on plague exposure pathways in prairie dogs and associated rodents to provide guidance to DOD partners regarding the potential for future outbreaks. Briefly, the specific objectives were to determine the relationship between local climate conditions and the prevalence of plague and other pathogens while assessing the ecological roles of specific rodent hosts and vector species in plague dynamics, evaluate flea intensity on rodent hosts and in burrows in relation to local climate conditions, and develop models to predict the impacts of climate change on plague dynamics.
Using data and samples collected during a large field study on the effectiveness of vaccination to manage plague in prairie dogs, the project team assessed rodent/flea assemblages, pathogen prevalence in fleas, and determined how local climate conditions influence flea development rates and relative abundance. Live animals (prairie dogs and some small rodents) were trapped to collect fleas and other samples on 46 prairie dog plots in six western states, many sites near DOD lands. At seven additional locations on a latitudinal gradient, fleas were collected from burrows several times per year to assess seasonality and effects of local climate conditions on flea abundance. These data were then used to develop predictive models that could be used to test specific hypotheses.
The project team determined that flea developmental rates, on-host flea abundance, species composition of the flea community, and burrow temperatures varied across a latitudinal gradient. Rodent and flea community composition and abundance differed geographically and were highly specialized with flea-switching between prairie dogs and short-lived rodents rare. Flea development rates, on-host flea abundance, and burrow temperatures increased with increasing ambient temperature. A large increase in the number of fleas found on a prairie dog colony, coupled with a greater number of infested burrows, could have meaningful impacts on plague dynamics in the western US as the climate warms. In addition to affecting flea load, climate change may also influence body condition of prairie dogs by reducing the amount of forage. This may result in animals being more tolerant of high flea loads (less engaged in grooming behavior) and more vulnerable to disease.
The project team has summarized information on flea communities and pathogen distribution in prairie dog populations across a broad range of species and geographic areas. The project team has developed a predictive model based on empirical data that can provide guidance regarding expected changes in plague frequency under different climate scenarios. These models can be used to estimate the potential effects of mitigation activities on the frequency and intensity of disease outbreaks which will benefit DOD in planning military exercises in areas affected by plague.