Interactions Amongst the Community of Endemic Pathogens of African Cattle: A Longitudinal Study in South East Uganda
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Date
03/2007Author
Tosas Auguet, Olga
Metadata
Abstract
The work presented in this thesis is focused upon the community of endemic pathogens of African
cattle in Sub-Saharan Africa, which has long constrained livestock production in these areas. The
first aim of this work is to investigate whether the pathogen community as a whole shapes the
ensuant epidemiology and morbidity which are currently attributed to any of its individual
pathogens. The second aim is to determine if a greater understanding of the interactions present
amongst genetically distinct parasites of the same species can be used to better explain
epidemiological features that are at present poorly understood. Emphasis is placed on examining
spatial variation in the epidemiology of Theileria parva, a tick-transmitted protozoan that causes
East Coast Fever.
To achieve these aims, this work examines field data collected from a large and comprehensive
study conducted in south east Uganda. Through application of apposite statistical techniques and
mathematical modelling, aspects of the complex relations amongst the pathogen community and
their environment are explored. Evidence is presented that demonstrates the paramount role of
the pathogen community as a whole in shaping the infection dynamics and pathogenicity of any of
its individual components. By focusing on a single member of this pathogen community (Theileria
parva), some of the influences of host, vector, geographical location, temporal dynamics and
intra-species pathogen interactions are elucidated. Application of a polymorphic molecular marker
to Theileria parva infected blood samples and the use of Cox proportional hazard analysis, show
variability in the survival of infections in cattle in high and low tick challenge areas. Moreover
infection survival, which plays a pivotal role in parasite transmission, is shown to be a function of
the interactions established amongst genetically distinct co-infective parasites. In consequence,
vector intensity alone is insufficient to develop reliable transmission models which can accurately
predict the epidemiology of the parasite inside and outside enzootic belts. Finally, a theoretical
model is developed which, based upon the field evidence obtained throughout this work, provides
a possible explanation for the mechanics of T. parva survival in cattle. In summary, this thesis makes a case that consideration of both inter- and intra-species pathogen interactions, can
greatly augment understanding of the epidemiology of these pathogen communities. An
integrated approach to pathogen dynamics can better equip an integrated approach to control of
important diseases of African cattle.