Prevalence and associations of Trypanosoma spp. and Sodalis glossinidius with intrinsic factors of tsetse flies

Trypanosomiasis has been identified as a neglected tropical disease in both humans and animals in many regions of sub-Saharan Africa. Whilst assessments of the biology of trypanosomes, vectors, vertebrate hosts and the environment have provided useful information about life cycles, transmission, and pathogenesis of the parasites that could be used for treatment and control, less information is available about the effects of interactions among multiple intrinsic factors on trypanosome presence in tsetse flies from different sites. It is known that multiple species of tsetse flies can transmit trypanosomes but differences in their vector competence has normally been studied in relation to individual factors in isolation, such as: intrinsic factors of the flies (e.g. age, sex); habitat characteristics; presence of endosymbionts (e.g. Wigglesworthia glossinidia, Sodalis glossinidius); feeding pattern; host communities that the flies feed on; and which species of trypanosomes are transmitted. The purpose of this study was to take a more integrated approach to investigate trypanosome prevalence in tsetse flies. In chapter 2, techniques were optimised for using the Polymerase Chain Reaction (PCR) to identify species of trypanosomes (Trypanosoma vivax, T. congolense, T. brucei, T. simiae, and T. godfreyi) present in four species of tsetse flies (Glossina austeni, G. brevipalpis, G. longipennis and G. pallidipes) from two regions of eastern Kenya (the Shimba Hills and Nguruman). Based on universal primers targeting the internal transcribed spacer 1 region (ITS-1), T. vivax was the predominant pathogenic species detected in flies, both singly and in combination with other species of trypanosomes. Using Generalised Linear Models (GLMs) and likelihood ratio tests to choose the best-fitting models, presence of T. vivax was significantly associated with an interaction between subpopulation (a combination between collection sites and species of Glossina) and sex of the flies (X2 = 7.52, df = 21, P-value = 0.0061); prevalence in females overall was higher than in males but this was not consistent across subpopulations. Similarly, T. congolense was significantly associated only with subpopulation (X2 = 18.77, df = 1, P-value = 0.0046); prevalence was higher overall in the Shimba Hills than in Nguruman but this pattern varied by species of tsetse fly. When associations were analysed in individual species of tsetse flies, there were no consistent associations between trypanosome prevalence and any single factor (site, sex, age) and different combinations of interactions were found to be significant for each. The results thus demonstrated complex interactions between vectors and trypanosome prevalence related to both the distribution and intrinsic factors of tsetse flies. The potential influence of the presence of S. glossinidius on trypanosome presence in tsetse flies was studied in chapter 3. A high number of Sodalis positive flies was found in the Shimba Hills, while there were only two positive flies from Nguruman. Presence or absence of Sodalis was significantly associated with subpopulation while trypanosome presence showed a significant association with age (X2 = 4.65, df = 14, P-value = 0.0310) and an interaction between subpopulation and sex (X2 = 18.94, df = 10, P-value = 0.0043). However, the specific associations that were significant varied across species of trypanosomes, with T. congolense and T. brucei but not T. vivax showing significant interactions involving Sodalis. Although it has previously been concluded that presence of Sodalis increases susceptibility to trypanosomes, the results presented here suggest a more complicated relationship, which may be biased by differences in the distribution and intrinsic factors of tsetse flies, as well as which trypanosome species are considered. In chapter 4 trypanosome status was studied in relation to blood meal sources, feeding status and feeding patterns of G. pallidipes (which was the predominant fly species collected for this study) as determined by sequencing the mitochondrial cytochrome B gene using DNA extracted from abdomen samples. African buffalo and African elephants were the main sources of blood meals but antelopes, warthogs, humans, giraffes and hyenas were also identified. Feeding on multiple hosts was common in flies sampled from the Shimba Hills but most flies from Nguruman had fed on single host species. Based on Multiple Correspondence Analysis (MCA), host-feeding patterns showed a correlation with site of sample collection and Sodalis status, while trypanosome status was correlated with sex and age of the flies, suggesting that recent host-feeding patterns from blood meal analysis cannot predict trypanosome status. In conclusion, the complexity of interactions found suggests that strategies of tsetse fly control should be specific to particular epidemic areas. Future studies should include laboratory experiments that use local colonies of tsetse flies, local strains of trypanosomes and local S. glossinidius under controlled environmental conditions to tease out the factors that affect vector competence and the relative influence of external environmental factors on the dynamics of these interactions.

Breaking old and new ground: a comparative study of coastal and inland naming in Berwickshire

This thesis investigates the place-names of four parishes in Berwickshire and compares coastal and inland naming patterns. Berwickshire is a large county that borders on northern England and historically formed part of Anglo-Saxon Northumbria. Partly due to the survival of extensive archives from the medieval priory of Coldingham, preserved in Durham Cathedral Archives, this county holds some of Scotland’s earliest recorded place- names. The parishes that form the research area are grouped together in the north-east of the county. Two of these parishes, Abbey St Bathans and Bunkle & Preston, are inland, and two, Cockburnspath and Coldingham, have extensive coastlines. The diversity of this group of parishes allows a comparative study of the place-names of coastal and inland areas to be undertaken. The topography of Berwickshire’s thirty-two parishes is very varied, and the four parishes have been chosen to reflect this range of landscapes. The place-names within the four parishes examined in this thesis derive almost exclusively from Old English, Older Scots, Modern Scots including Standard Scottish English, with a small minority derived from Old Norse, Gaelic, and Brittonic. The chronology of Old English, Older Scots, and Modern Scots is defined as given in the Concise Scots Dictionary: Old English is the period up to 1100, Older Scots is the period 1100-1700, and Modern Scots is the period 1700 onwards (CSD, 1985: xiii). Often with place-names it is not possible to give a precise dating for the coining of a toponym. For the purposes of this study, the language label given for a toponym is that of the date of the earliest record of the place-name with earlier linguistic evidence supplementing discussion. This thesis focuses on the names of topographic features, for example hills, rocks and woodland, and the role of perception in their naming. In order to compare the role of perception in inland and coastal naming, this thesis includes a diachronic study of the toponymy of the research area, along with two case studies. The first of these is a study of the toponymy of relief features, which focuses on generic elements in order to compare the perception of one type of referent in the two environments. The second is a study of the ‘colour’ category, which focuses on qualifying elements in order to compare the use of colour terms in the two environments. This thesis is the first comparative study of inland and coastal place-names, and it is one of the first to investigate new ways of using fieldwork as a central part of its methodology. In doing so it proposes innovative and nuanced ways to understand the toponymy of diverse landscapes within a community.