For vector-borne parasites such as malaria, how within- and between-host processes interact to shape transmission is poorly understood. In the host, malaria parasites replicate asexually but for transmission via mosquitoes to occur, specialized sexual stages (gametocytes) must be produced. Once inside the mosquito vector, gametocytes immediately differentiate into male and female gametes, and motile male gametes must swim through the hostile environment of the bloodmeal to find and fertilise female gametes. Despite the central role that gametocytes play in disease transmission, explanations of why parasites adjust gametocyte production in response to in-host factors remain controversial. Furthermore, surprisingly little is known about the mating behaviour of malaria parasites once inside the mosquito. Developing drugs and/or vaccines that prevent transmission by disrupting sexual stages are major goals of biomedicine, but understanding variation in gametocyte investment and male gamete behaviour is key to the success of any intervention. First, I propose that the evolutionary theory developed to explain variation in reproductive effort in multicellular organisms provides a framework to understand gametocyte investment strategies in malaria parasites. I then demonstrate that parasites appear to change their reproductive strategies in response to environmental cues and in a manner consistent with our predictions. Next, I show how digital holographic microscopy can be used to characterise the morphology and motility of male gametes. I then provide evidence for non-random movement of male gametes and that gamete interactions with red blood cells appear to hinder mating success in a bloodmeal. Finally, I discuss the variation in gametocyte differentiation and fertilisation success when exposed to a number of factors implicated in gametocyte activation. The data presented here provides important information on the basic biology of malaria parasite reproductive stages and demonstrates considerable variation in parasite traits and behaviours in response environmental changes; both in the host and in the mosquito vector.

Fragmentation can drive local populations to become smaller and more isolated, and consequently more susceptible to extinction. Movement between patches, however, can interconnect such populations so that they effectively behave as larger and more stable metapopulations. Over the past two decades metapopulations have been used to shed light on the complex interactions that occur between hosts and parasites. Effectively every host can be considered as a discrete habitat patch from the perspective of a parasite. As such, host-parasite interactions naturally lend themselves to being examined within the metapopulation paradigm. In this thesis I examine empirically how various aspects of metapopulation structure, such as local host population size and landscape isolation/connectivity, combine to determine the extinction and recolonization dynamics of parasites in the landscape. Using a naturally fragmented water vole (Arvicola amphibious) metapopulation, I describe the spatial and temporal variation in parasite infection prevalence or burden in a Scottish landscape. I specifically address the spatial and temporal dynamics of both ectoparasites, and vectortransmitted microparasites, since these are two groups of parasites commonly found in natural systems yet often overlooked in the host-parasite metapopulation literature. In addition, I attempt to understand how specific parasite characteristics, such as transmission mode and infectious period, can influence how parasites respond to host population structure. In the final chapter, I bring together a number of parasite groups to examine the impact of metapopulation dynamics on parasite communities as a whole by investigating its impact of parasite community richness. Overall the findings of my study indicate that host spatial structure and the level of connectivity between patches are important factors that affect parasite dynamics and community richness. However, the exact level of connectivity required to sustain a parasite population locally depended on specific parasite characteristics. In contrast, local effects host/vector population size and patch infection history) had no discernible impact on most parasite groups.

Many zoonotic pathogens of concern to human and veterinary health are maintained in the environment within small mammal reservoirs and vectored to new hosts by ectoparasitic arthropods. While the ecological relationships among small mammals, ectoparasites, and disease-causing symbiotic microorganisms are important to these dynamics, little is known about them across much of North America. The sylvatic cycle of Borrelia burgdorferi, the etiologic agent of Lyme disease, is of particular interest because Lyme disease is the most common vector-borne disease of humans in the United States. However, cases of Lyme disease are primarily confined to the northeastern and Midwestern United States, with only sporadic cases extending into the southeast. As a result, much of what is known of the ecology of Lyme disease comes from studies conducted in those regions. The goal of this study was to examine the ecological dynamics of the B. burgdorferi/vector/reservoir system in south-central Kentucky and gain insight into the relative paucity of Lyme disease in Kentucky. Small mammals were captured using live traps in three 200x50 m trapping grids within Western Kentucky University’s Green River Preserve from November 2014-October 2015. Captured small mammals were identified to species and standard measurements were recorded. Ectoparasites were removed and retained for identification. Collected blood and tissue were examined for B. burgdorferi DNA by polymerase chain reaction with primers specific to the OspA gene. The Bray-Curtis dissimilarity index, Schnabel population estimates, and the Shannon-Wiener diversity index were used to assess the structure of the small mammal communities. Parasite infestation was low but was affected by age and sex of the host, site, and season in different parasite taxa. Infestation by Ixodes scapularis, the primary vector for B. burgdorferi, was uncommon and prevalence of B. burgdorferi in blood was similar to the lowest prevalence previously observed in the Lyme disease endemic regions. We found that life history characteristics of hosts and ectoparasites drive their associations. We also suggest that the lack of an efficient vector for B. burgdorferi is the likely explanation for the few reported cases of Lyme disease in Kentucky.

published_or_final_version / Zoology / Master / Master of Philosophy

Various biological relationships between the myramid egg parasite, Anaphes ovijentatus (Crosby and Leonard), and its hosts were studied. Eggs of the four major species of Lygus that occur on crops were highly parasitized. Other mirid hosts in southern Arizona were collected from weeds in agricultural areas. Small numbers of Nabis alternatus Parshley and N. americoferus Carayon, predators of several insect pests, were parasitized in the laboratory. The membracid Spissistilus festinus (Say) was an infrequent host. Parasitism of L. hesperus was similar (82-88%) for eggs 1-6 days old at 25°C, but parasitism of 7-day-old eggs was significantly reduced (18.9%). Parasitism must occur at least 24 hours prior to host egg hatch to be successful; the period of time required for A. ovijentatus egg development. Anaphes ovijentatus developed from egg to adult in L. hesperus eggs at a constant temperature of 12.8°C and at variable regimes with means of 12.8, 10.6, and 32.8°C. An average of 26 progeny per female were produced at the variable 12.8 and 10.6°C regimes, only a few progeny were produced at a constant 12.8°C and none were produced at the variable 32.8°C regime. Lygus hesperus eggs hatched at all four temperature regimes, but nymphs survived to adulthood only at the variable regimes of 12.8 and 10.6°C. Total egg to egg periods at the variable 12.8°C was approximately 103 days for L. hesperus and about 54 days for A. ovijentatus. The majority of the L. hesperus eggs were deposited in the upper halves of cotton, alfalfa, and the crucifer Sisymbrium irio L. plants. L. hesperus deposited more eggs in alfalfa than in cotton plants, but showed no preference between alfalfa and S. irio. Anaphes ovijentatus did not demonstrate clear preferences for L. hesperus eggs in any plant species or plant section.

Gastrointestinal parasitism in grazing lambs adversely affects animal performance and welfare, causing significant production losses for the sheep industry. Control of gastrointestinal parasitism using chemotherapeutic treatment is under threat due to the emergence of anthelmintic resistance, thus stimulating research into alternative control strategies. Whilst investigating control strategies experimentally can be costly and time consuming, using a mathematical modelling approach can reduce such constraints. A previously developed model which describes the impact of host nutrition, genotype and gastrointestinal parasitism in a growing lamb, provided an appropriate starting point to explore control strategies and their impact on host-parasite interactions. Two contrasting mechanisms have previously been proposed to account for the occurrence of anorexia during parasitism. These were reductions in either intrinsic growth rate or relative food intake. Thus, the existing individual lamb model was modified to evaluate these mechanisms by exploring the relationship between anorexia and food composition (Chapter 2). For foods that did not constrain food intake, published data was found to be consistent with the predictions that arose from anorexia being modelled as a reduction in relative food intake. Reported genetic parameter estimates for resistance and performance traits appear to vary under differing production environments. In order to explore the impact of epidemiological effects and anthelmintic input on genetic parameter estimates the model was extended to simulate a population of lambs in a grazing scenario (Chapter 3). Whilst estimates of heritabilities and genetic correlations for drenched lambs remained constant, for lambs given no anthelmintic treatment, the heritability of empty body weight (EBW) reduced and the genetic correlation between faecal egg count (FEC) and EBW became increasingly negative with increasing exposure to infective larvae. Thus differences in anthelmintic input and pasture larval contamination (PC) may provide plausible causes for the variation in genetic parameter estimates previously reported. To investigate the interactions between host resistance and epidemiology (Chapter 4) a population of 10,000 lambs were simulated and FEC predictions used to assign the 1,000 lambs with the highest and lowest predicted FEC to ‘susceptible’ (S) and ‘resistant’ (R) groups, respectively. R and S groups were then simulated to graze separate pastures over 3 grazing seasons. The average FEC and PC predictions of these groups diverged during the first 2 grazing seasons and stabilised during the third, such that the difference in FEC predictions between R and S groups were double those predicted when grazed with the population. This was found to be consistent with experimental data. Further, anthelmintic treatment and grazing strategies were predicted to have no impact on the EBW of resistant lambs, suggesting that control strategies should be targeted towards susceptible animals. Targeted selective anthelmintic treatment (TST) has been proposed to reduce risks of anthelmintic resistance with minimal impacts on performance. To describe the short- and long-term impacts of TST and drenching frequency on sheep production and the emergence of anthelmintic resistance, the model was extended to include a description of anthelmintic resistance genotypes within the nematode population (Chapter 5). Reducing the proportion of treated animals was predicted to increase the duration of anthelmintic efficacy, whilst reducing the drenching frequency increased the long-term benefits of anthelmintic on sheep production. Various determinant criteria for use in TST regimes were compared (Chapter 5) including performance traits such as live weight and growth rate, and parasitological traits such as FEC. Using FEC as the TST criterion was predicted to allow the greatest reduction in the number of anthelmintic treatments administered whilst maintaining the highest average EBW, whilst live weight and growth rate were predicted to give little to no improvement in comparison to selecting animals at random for TST. Using estimated breeding values (EBVs) for FEC as the determinant criterion for TST regimes was compared to using measured FEC (Chapter 6). The EBV for true FEC across the entire growth period, akin to perfect genomic selection, was predicted to be a better criterion than measured time-specific FEC (including a sampling error) for a TST regime. EBVs calculated using measured time-specific FEC showed little benefit compared to measured FEC. The information gained from these simulation studies increases our understanding of control strategies and their impact on host-parasite interactions under various scenarios that may not have been possible using experimental methods. It is important to remember that the aim of alternative or complimentary control strategies is to maintain the sustainability of sheep production systems, and as such the production gain of any control strategy needs to be weighed against the financial, labour and time costs involved in implementation.

La compréhension des processus microévolutifs ayant lieu dans la nature nécessite la quantification des principales forces sélectives s'exerçant sur les populations sauvages. Ces 10 dernières années, les études à long terme et l'écologie de la résurrection (qui fait revivre des stades en dormance) ont été les principales approches pour étudier l'évolution des traits d'histoire de vie sur plusieurs générations dans les populations sauvages. Mon travail consiste à comprendre comment des facteurs écologies simples (p. ex. la température) et des interactions interspécifiques ou intraspécifiques plus complexes (p. ex. les interactions antagonistes hôte-parasite ou mâle-femelle) façonnent le processus évolutif des populations sauvages. Dans cette optique, j'ai utilisé l'Artémia comme un organisme modèle, en combinant des études sur le terrain et en laboratoire. Premièrement, j'ai étudié l'évolution de la niche thermique avec une approche d'écologie de la résurrection, en utilisant une série temporelle d'œufs de dormance d'une population d' introduite à partir de marais salants de régions tempérées dans des marais salants tropicaux dans les années 80. Cette étude montre que la survie aux températures élevées (caractéristiques du nouvel environnement) a augmenté linéairement au cours du temps à partir de l'introduction, suggérant un taux d'adaptation constant sur plus de 100 générations. Deuxièmement, j'ai utilisé une approche similaire pour étudier l'adaptation entre males et femelles dans une autre population d'Artémia. Cette étude suggère que les conflits sexuels provoquent une dynamique de coévolution fluctuante dans la nature sur une échelle d'environ 100 générations. Troisièmement, j'ai étudié les impacts respectifs de différents parasites (une espèce de cestode et deux espèces de microsporidie) sur la compétition entre une espèce d'hôte autochtone asexuée et une espèce d'hôte invasive sexuée. Chacun des trois parasites étaient soit spécialiste d'une espèce ou de certains génotypes d'hôte. De plus, l'espèce de cestode dont l'effet castrateur chez l'hôte est bien connu infectait uniquement l'espèce autochtone, suggérant que ce parasite joue un rôle majeur dans la compétition entre les espèces d'hôte autochtones et invasives. Par ailleurs, les trois espèces de parasite semblaient manipuler le comportement d'agrégation de leur hôte, très probablement pour augmenter leur transmission à de nouveaux hôtes. Enfin, j'ai réalisé des études de génétiques des populations d'espèces asexuées diploïdes et polyploïdes d'Artemia et d'espèces sexuées asiatiques proches. Les espèces asexuées diploïdes produisent des mâles rares et il semblerait que ceux-ci permettent une faible fréquence de reproduction sexuée. De plus, l'hybridation d'espèces d'Artémia éloignée phylogénétiquement a donné naissance à au moins trois lignées polyploïdes indépendantes. / Getting a comprehensive understanding of microevolution in natural populations requires proper quantification of the important selective forces exerted on these populations. Over the last decade, long-term studies and resurrection-ecology (revival of resting stages) have been the main approaches to study life history trait evolution over many generations in the wild. My work aims at understanding how simple ecological factors (e.g. temperature) and complex interactions between and within species (host-parasite and male-females antagonistic interactions) shape evolutionary processes in natural populations. To this end, I used the brine shrimp Artemia as a model system and combined laboratory and field studies. First, I investigated thermal niche evolution with a resurrection ecology approach, using dormant-egg time series from an Artemia population introduced from temperate to tropical salterns in the mid-80's. This experiment shows that survival at the high temperatures typical of the new environment increased linearly through time after the introduction, suggesting a sustained rate of adaptation over more than 100 generations. Second, I used the same approach to study adaptation between sexes in another Artemia population. I found that sexual conflicts result in fluctuating male-female coevolutionary dynamics in natura, over a time scale of ~100 generations. Third, I studied the relative role of one cestode and two microsporidian parasites in mediating the competition between a native asexual host and an invasive bisexual host. I found that all three parasites were either host- or genotype-specific and that the castrating cestode parasite specifically infected the native species, suggesting that this parasite actually played a major role in the competition between native and invasive hosts. Interestingly, all three parasites manipulated the swarming behavior of their host, most likely to increase their transmission. Fourth, I performed population genetic studies of diploid and polyploid Artemia parthenogenetica and their Asian bisexual close relatives. Diploid asexual Artemia produce rare males and I found indication that these males allow some rare sex in this otherwise parthenogenetic species. In addition, hybridization between divergent Artemia species has led to the origin of at least three independent polyploid lineages.

The most virulent malaria parasite, Plasmodium falciparum, makes use of extensive antigenic diversity to maximise its transmission potential. Parasite genomes contain several highly polymorphic gene families, whose products are the target of protective immune responses. The best studied of these are the PfEMP1 surface proteins, which are encoded by the var multi-gene family and are important virulence factors. During infection, the parasite switches expression between PfEMP1 variants in order to evade adaptive immune responses and prolong infection. On the population level, parasites appear to be structured with respect to their var genes into non-overlapping repertoires, which can lead to high reinfection rates. This non-random structuring of antigenic diversity can also be found at the level of individual var gene repertoires and var genes themselves. However, not much is known about the evolutionary determinants which select for and maintain this structure at different ecological scales. In this thesis I investigate the mechanisms by which multi-scale immune selection and other ecological factors influence the evolution of structured diversity. Using a suite of theoretical frameworks I show that treating diversity as a dynamic property, which emerges from the underlying infection and transmission processes, has a major effect on the relationship between the parasite’s transmis- sion potential and disease prevalence, with important implications for monitoring control efforts. Furthermore, I show that an evolutionary trade-off between within-host and between-host fitness together with functional constraints on diversification can explain the structured diversity found at both the repertoire and parasite population level and might also account for empirically observed exposure-dependent acquisition of immunity. Together, this work highlights the need to consider evolutionary factors acting at different ecological scales to gain a more comprehensive understanding of the complex immune-epidemiology of P. falciparum malaria.

Made available in DSpace on 2016-04-28T20:15:23Z (GMT). No. of bitstreams: 1 1990-Ruth Miriam Alva Fernandez.pdf: 795004 bytes, checksum: 0fa06a19352e7709d3b42d96b1490723 (MD5) Previous issue date: 1990-05-10 / Conselho Nacional de Desenvolvimento Cient?fico e Tecnol?gico / Steers were used as experimental host for Amblyomma cajennense and Boophilus microplus during simultaneous infections on ears and quarters. Thus, the study shows especifically teleoginas and quenoginas weight, egg production, eclodibility and oviposition period. The ticks were held in laboratoryconditions at 27?C and 70% UR. It was observed that teleoginas collected from the ears were lighter than those collected from hind quarters. Egg production index (EPI) and nutrient efficiency index (NEI) for A. cajennense was 45,74% and 60,36%, respectively, and for B. microplus was 42,58% and 59,51%, respectively. The eclodibility index from simultaneous infection was lower than individual infections. The correlation between teleogina weight and egg production for both ticks specie showed that the number of eggs was influenced by teleogina weight. The interaction between A. cajennense and B. microplus is reported for simultaneous infection on bovine. / Utilizando bovinos como hospedeiros, avaliou-se o comportamento de Amblyomma cajennense e Boophilus microplus em infesta??es simult?neas na orelha e anca, essa em ?reas de aproximadamente 60 cm2. O estudo focalizou prioritariamente o peso das tele?ginas, das quen?ginas, a produ??o de ovos, o tempo de ovipostura e a eclodibilidade. Os carrapatos foram criados em laborat?rio em estufa do tipo B.O.D. com temperatura controlada de 27? C e unidade relativa de 70 ? 10%, e mantidos isoladamente ap?s desprendimento do hospedeiro nas mesmas condi??es laboratoriais. As tele?ginas que ingurgitaram na orelha pesaram menos que as alimentadas nas ancas em ambas as esp?cies; o ?ndice de produ??o de ovos (IPO) e o ?ndice de efici?ncia nutricional (IEN) para A. cajennense e B. microplus foram 45,74 e 42,58%, e 60,36 e 59,5%, respectivamente. As taxas de eclodibilidade foram menores que as j? assinaladas para infesta??es individuais nas duas esp?cies. A correla??o entre o peso da tele?gina das duas esp?cies e a produ??o de ovos foi significativa, comprovando ser o n?mero de ovos ovipostos fun??o do peso da f?mea antes do ?nicio da postura. Concluindo-se haver intera??o entre A. cajennense e B. microplus em infesta??o simult?nea em bovinos.

Further functional investigation revealed that knockdown of GRP78 expression by RNA interference resulted in a significant increase of both intracellular and extracellular HBV virions in the transient HBV-producing HepG2 cells, concomitant with enhanced levels of hepatitis B surface antigen and e antigen in the culture medium Conversely, overexpression of GRP78 in HepG2 cells led to HBV suppression concomitant with induction of the positive regulatory circuit of GRP78 and interferon-beta 1 (IFN-beta1). In this connection, IFN-beta1-mediated 2', 5'-oligoadenylate synthetase (OAS) and ribonuclease L (RNase L) signaling pathway was noted to be activated in GRP78-overexpressing HepG2 cells. Moreover, GRP78 was significantly down-regulated in the livers of chronic hepatitis B patients after effective anti-HBV treatment (p= 0.019) as compared with their counterpart pre-treatment liver biopsies. / Hepatitis B virus (HBV) infection is a global public health problem, which plays a crucial role in the pathogenesis of chronic hepatitis, cirrhosis and hepatocellular carcinoma. Although considerable progress has been made over the past decade, the pathogenesis of HBV infection and the mechanisms of host-virus interactions are still elusive. / In conclusion, the present study demonstrates for the first time that GRP78 functions as an endogenous anti-HBV factor via IFN-beta1-OAS-RNase L pathway in hepatocytes. Induction of hepatic GRP78 may provide a novel therapeutic approach in treating HBV infection. / In this study, we applied a two-dimensional gel electrophoresis and mass spectrometry-based comparative proteomic approach to globally analyze the host early response to HBV by using an inducible HBV-producing cell line HepAD38. Twenty-three proteins were identified as differentially expressed, with glucose-regulated protein 78 (GRP78) as one of the most significantly up-regulated proteins induced by HBV replication. This induction was further confirmed in both HepAD38 and HepG2 cells transfected with HBV-producing plasmids by real-time reverse transcription-polymerase chain reaction (RT-PCR) and Western blotting, as well as in HBV-infected human liver biopsies by immunohistochemistry. / Ma, Yan. / Adviser: Ming-Liang He. / Source: Dissertation Abstracts International, Volume: 72-01, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references (leaves 111-129). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. Ann Arbor, MI : ProQuest Information and Learning Company, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.