|dc.description.abstract||Unravelling the complexities of a disease with multiple wildlife host and multiple tsetse
vector species is no easy task. After over a century of field observations, experimental
studies, anecdotal evidence and conjecture, the role of wildlife in the transmission of
trypanosomes is still unclear. Recently, however, frameworks used in the studies of other
vector-borne diseases with wildlife reservoirs showed that not only is it possible to
understand transmission, but that spatio-temporal predictions of human disease risk and
targeted control are realistic aims, even in such complex systems. This thesis explores the
epidemiology of human African trypanosomiasis (HAT) in the Serengeti-Mara ecosystem in
Northern Tanzania, where recent cases in tourists have highlighted the disease as a public
health and economic concern.
Assessment of the prevalence of trypanosome infections in different wildlife species is the
first step in investigating the relative importance of different species in disease transmission.
Identification of trypanosomes relies on sensitive and specific diagnostic tests. Polymerase
chain reaction (PCR) protocols based on interspecies differences in the length of the
ribosomal internal transcribed spacer (ITS) regions have been widely used in livestock to
identify multiple trypanosome species in one PCR reaction. This study represents the first
assessment of these protocols on blood samples collected from wildlife. Clonal sequence
analysis of PCR products revealed a large range of trypanosomes circulating in wildlife,
including Trypanosoma congolense, Trypanosoma brucei, Trypanosoma simiae Tsavo,
Trypanosoma godfreyi and Trypanosoma vivax. In addition sequences similar to known
sequences, termed Trypanosoma simiae-like and T. vivax-like trypanosomes, may reflect
further diversity. However, further characterisation is needed before ITS protocols can be
used widely for epidemiological studies in wildlife.
The prevalence of T. brucei s.l. and T. congolense varied widely between species. This
variation was predominantly explained by taxonomic classification, suggesting intrinsic
differences in response to trypanosomes. Trypanosoma brucei rhodesiense, the subspecies
responsible for HAT, was identified in lion, hyaena and reedbuck. Age significantly affected
the prevalence of T. congolense in lion and hyaena, with the highest prevalence in subadults.
The lack of statistically significant differences in prevalence between animals
sampled live or after death confirmed that post-mortem sampling provides a method for
increasing sample sizes in wildlife studies. The complex relationship between tsetse density
and prevalence of trypanosome infections illustrated the difficulties of assessing data from
diverse ecosystems with many potential confounding factors.
A cross-sectional study of Glossina swynnertoni and Glossina pallidipes, the main tsetse
species in Serengeti, highlighted the difficulties of integrating the results of microscopy and
PCR to generate meaningful measures of the prevalence of transmissible T. brucei infections
for epidemiological studies. However, PCR results suggested that G. pallidipes may be more
important as a vector of T. brucei s.l. than has been previously recognised. Spatial variation
in both tsetse density and the prevalence of trypanosome infections suggests human disease
risk is heterogeneous.
The results of this study, along with relevant literature, are considered within the context of
frameworks used for other vector-borne diseases and the implications for disease