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Disease Invasion and Control in Structured Populations



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Disease Invasion and Control in Structured Populations Bovine Tuberculosis in the Buffalo Population of the Kruger National Park by Paul Chafee Cross B A University of Virginia 1998 A dissertation submitted in partial satisfaction of the requirements for the degree of Doctor of Philosophy in Environmental Science Policy and Management in the GRADUATE DIVISION of the UNIVERSITY OF CALIFORNIA BERKELEY Committee in charge Professor Wayne M Getz Chair Professor Steven R Beissinger Professor Cheryl J Briggs Professor Johan T du Toit May 2005 Disease Invasion and Control in Structured Populations Bovine Tuberculosis in the Buffalo Population of the Kruger National Park 2005 by Paul Chafee Cross Abstract Disease Invasion and Control in Structured Populations Bovine Tuberculosis in the Buffalo Population of the Kruger National Park by Paul Chafee Cross Doctor of Philosophy in Environmental Science Policy and Management University of California Berkeley Professor Wayne M Getz Chair From 1991 to 2004 bovine tuberculosis Mycobacterium bovis BTB moved north and increased in prevalence in the African buffalo Syncerus caffer population of the Kruger National Park South Africa I use this epidemic as a case study to understand how host population structure affects disease dynamics Radio tracking data indicated that all sex and age groups moved between herds but males over eight years old had higher mortality and dispersal rates than any other sex or age category BTB appeared to have only minor effects upon survival Models incorporating these data suggest that the success of vaccination programs will depend strongly upon the duration that a vaccine grants protection which is currently unknown Even with a lifelong vaccine 1 however eradication is unlikely unless vaccination is combined with other control strategies To analyze the radio tracking and association data I proposed a new metric of association the fission decision index FDI that significantly reduces the biases that exist in traditional association analyses in fission fusion societies Adult female and juvenile buffalo made non random fission decisions while adult male choices were indistinguishable from a random coin toss Incorporating the association data into a dynamic social network model suggested that the dynamic nature of the network has a strong influence on disease dynamics particularly for diseases with shorter infectious periods Buffalo herds were more tightly associated in 2002 than 2003 perhaps due to drier conditions in 2003 prompting additional movement that would facilitate the spread of disease among herds Using a metapopulation model I illustrate how the group level metric R which is the average number of groups infected by the initial group is a better predictor of disease invasion than the traditional individual level R0 in structured host populations R is a function of group size movement rate infection rate and length of the infectious period Chronic diseases allow for more host mixing between groups thus they perceive a more well mixed host population As a result chronic diseases are more likely to invade structured populations than acute diseases given the same R0 and it is more important to incorporate the spatial structure of the host population for acute diseases than chronic diseases 2 Table of Contents Acknowledgements ii Chapter One 1 Chapter Two 8 Chapter Three 39 Chapter Four 61 Chapter Five 92 References 118 i Acknowledgements First I would like to thank my family for all of their support Craig Hay Justin Bowers Julie Wolhuter Khutani Bulunga and Augusta Mabunda collected the vast majority of the field data included in this dissertation Always professional and great companions they made the last four years in Satara an amazing experience I am grateful to the managers scientists and staff of the Kruger National Park for facilitating the project and to the United States National Science Foundation Ecology of Infectious Disease Grant DEB 0090323 for funding this research Drs Markus Hofmeyr Peter Buss Lin Mari de Klerk Roy Bengis and Douw Grobler as well as Marius Kruger KNP Game Capture State Veterinary technicians and many University of Pretoria students assisted in buffalo capture operations Roy Bengis Steve Beissinger Cherie Briggs Justin Brashares Charlie Nunn and Anna Jolles all provided many helpful comments along the way Martin Haupt and Elmarie Cronje at the University of Pretoria were invaluable in their assistance with equipment and finances All the students in the Getz Lab including Peter Baxter Chris Wilmers Sadie Ryan Andy Lyons Allison Bidlack Wendy Turner Shirli Bar David John Eppley George Wittemyer James Lloyd Smith and Karen Levy made it a fantastic environment to work in In particular Jamie Lloyd Smith and George Wittemyer were a great support and source of ideas and inspiration throughout this dissertation Lastly I would like to thank Molly Smith Johan du Toit and Wayne Getz To list all the ways that they helped would be its own dissertation ii Chapter One Summary P C Cross 1 Bovine tuberculosis BTB caused by Mycobacterium bovis is an airborne bacterial pathogen that is re emerging in wildlife and livestock worldwide In the Kruger National Park KNP of South Africa BTB is increasing in prevalence and moving northwards from its introduction from cattle along the southern border of the KNP in the early 1960s Bengis et al 1996 Bengis 1999 Rodwell et al 2001 African buffalo Syncerus caffer caffer are a reservoir host maintaining the disease at high prevalence over 50 in some herds while predators such as lions and leopards appear to be spillover hosts Keet et al 1996 Rodwell et al 2000 It remains unclear how the effects of BTB with its wide range of potential hosts will ripple through the KNP ecosystem Caron et al 2003 Furthermore Kruger National Park is the largest reserve in South Africa covering over 20 000 km2 and is the source of many animal translocations BTB may limit the ability of KNP managers to translocate animals from the KNP thereby decreasing a potential source of revenue for South African National Parks and creating a conservation island This dissertation is one component of a larger research program on BTB in the buffalo population of the KNP the goal of which is to develop a better understanding of disease dynamics in wildlife systems as well as to evaluate potential management strategies Here I investigate the role of host social and spatial structure on the spread and


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