This project focuses on brucellosis, a bacterial infection of elk, bison and cattle in the Greater Yellowstone Ecosystem. Since 2004, several instances of brucellosis transmission from wildlife to livestock have resulted in cattle outbreaks in Wyoming, Idaho, and Montana. This research will provide critical scientific information to the multiple State and Federal agencies responsible for wildlife and livestock in this region. The specific research objectives are to: (1) determine whether brucellosis prevalence of elk can be reduced on the supplemental feedgrounds of Wyoming using two ecological field manipulations; (2) determine the effects of changing land-ownership, irrigation, predation, and hunting on elk group size distributions and brucellosis prevalence; and (3) estimate the amount of intraspecific brucellosis transmission among elk populations and the interspecific transmission among elk, bison, and cattle using a combination of host and pathogen DNA markers and genomics.
The researchers will assess how contact and disease transmission are related to host aggregation, and how host aggregations, in turn, are affected by land-use, habitat, hunting, and predators. The relationship between host density and parasite transmission is fundamental to understanding the dynamics of infectious disease transmission. Models predict that when transmission is correlated with host density, there is a host density threshold below which the parasite will be unable to persist as the density is reduced. This forms the basis for using social distancing (such as school closures) to reduce the spread of pandemics. In natural systems, the density-transmission relationship is the justification for strategies such as culling, sterilization, and vaccination, which aim to reduce the density of susceptible individuals.
The problem of managing Brucella in the Greater Yellowstone Ecosystem is of direct and immediate importance for wildlife management and conservation in this flagship American ecosystem. The researchers will provide information to natural resource managers through biennual meetings and will disseminate free novel software for genetic analyses of pathogen dynamics. The project also will: provide research and training opportunities for undergraduate and graduate students, with a particular goal of recruiting Native American students; foster the participation of scientists in programs with GK-12 teachers and students; and support public outreach through films and podcasts developed by students in the Science and Natural History Filmmaking program at Montana State and through the educational outreach program at Yellowstone National Park.
This project was intended to answer general questions about how host density affects disease transmission as well as specific questions about brucellosis, a bacterial infection of elk, bison and cattle in the Greater Yellowstone Ecosystem (GYE). Brucellosis appears to be expanding in the elk population of the GYE and there is significant uncertainty about how to best protect overlapping cattle herds. Understanding how diseases are transmitted in different populations is relevant to natural resource managers who may alter hunting pressure or public health officials that may recommend limiting large gatherings and school attendance during a major outbreak. We found that at the individual level, contacts and thus transmission, are likely to increase as elk group sizes get larger. In addition, as elk populations increase so do the sizes of the largest groups in that population. As a result, disease transmission appears to be linked to host density at both local and broader scales in the elk population, but the relationship gets weaker at broader spatial scales. This is not true for all host species. For example, we have also worked on disease issues in bison and bighorn sheep. In both of these species, local group sizes stay the same even though the total population size may increase or decrease. As a result, even though transmission at the local scale may increase with larger group sizes, reducing the total population size at a broad scale is unlikely to affect the local transmission. For elk around the GYE, we found that the largest elk groups are likely to be on flatter and more open habitats, which may create additional conflicts with livestock. We also found that some elk are likely to become test-negative later in life, after initially testing positive. This is probably due to antibodies that decay over time in an infected individual. This project has lead us to several ongoing research efforts: whole genome sequencing of the brucellosis isolates to assess cross-species transmission as well as predicting the future spread of brucellosis in the GYE.
