Dissertations / Theses on the topic 'Host-parasite relationships Immunological aspects'

Ticks are obligate haematophagous arthropods that represent a major economic drain upon the world's livestock as well being a significant medical and veterinary risk through the transmission of tick-borne pathogens such as Borrelia burgdorferi, the causative agent of Lyme disease. The tick-host relationship is a function of both ecological and physiological factors. Successful feeding requires the effective acquisition and digestion of a bloodmeal by the tick. Acquisition relies upon the ability of the tick to counteract host immune responses induced by the extended feeding periods of ixodid ticks (up to 2 weeks). The host response to tick infestation and the consequent countermeasures employed by the tick, constitute the tick-host interface. The immune response of hosts to Ixodes ricinus infestations was examined through antigenic profiling. The antigens exposed to the host were shown to vary throughout the feeding period and differed between the different development stages of I. ricinus. It was also shown that different host species infested with I. ricinus recognised different antigens. This was true of both natural and non-natural hosts, and even closely related species. Anti-complement activity was investigated in the salivary glands of Ixodes ticks. This activity was shown to inhibit some host species but not others. The pattern of inhibitory activity varied between the tick species tested in a way that was consistent with known tick host-preferences. The mechanisms of anti-complement activity in I. ricinus salivary glands were explored. The alternative but not the classical pathway of complement was inhibited. Activity was present in unfed ticks and throughout the feeding period. Three targets of the complement system were identified as being modulated by the tick. Digestion of the bloodmeal was explored and a haemolytic activity was associated with the salivary glands of I. ricinus ticks. The activity was demonstrated to be Mg²⁺- dependent. In addition, a subtractive cDNA library enriched for saliva-associated transcripts was successfully produced. Random sampling identified putative differentially expressed genes. The results of this thesis illustrate the complexity of tick-host interactions at the molecular level. It is apparent that the research described poses many more questions than answers.

Biological and immunological aspects of the host-parasite relationship were examined in mice which are susceptible (A/J) and resistant (B10.A) to Giardia muris. B10.A exhibited a shorter latent period, lower cyst output during the acute phase of the infection and shorter period of cyst release compared to A/J. Characteristics of the infection transmitted from mouse-to-mouse and those induced by oral inoculation with cysts or trophozoites were similar. The infection was longer in male A/J and B10.A mice compared to females. Susceptibility and resistance during both the acute and elimination phases of the infection were under non-H-2-linked multigenic control. A/J and B10.A differed in non-specific serum IgG and IgA, but not in the specific IgG and IgA to G. muris. Specific antibodies participated in complement-mediated killing of trophozoites. Spleen, mesenteric lymph node and peritoneal cells from A/J and B10.A mice had a similar ability to kill trophozoites. The capacity of B10.A to mount inflammatory responses was greater than that of A/J. A/J were more immunosuppressed than B10.A during the infection, particularly at mucosal sites. Macrophage-like suppressor cells were shown to be the mediators of this suppression.

The relationships among parasite growth, responses to infection and host genetic factors were examined in rodents infected with Echinococcus multilocularis. Mongolian gerbils, cotton rats and C57L/J mice were relatively susceptible to the infection, whereas five other inbred strains of mice, and hybrids and backcrosses between C57L/J and C57BL/6J mice were more resistant. In mice, susceptibility to E. multilocularis was controlled by multiple, non-H-2-linked genes, as were pathological, inflammatory and specific (antibody) responses to the infection. These responses were also affected by the degree of parasite growth in individual hosts. Antibodies, natural killer cells and hematological responsiveness were ruled out as contributing to resistance to E. multilocularis. Studies on peritoneal leukocytes from infected animals suggested that infections with E. multilocularis were controlled by cells in two phases: an acute phase involving neutrophils and mononuclear cells and a chronic phase involving eosinophils and mononuclear cells.

Argulus foliaceus (Linnaeus, 1758) is a member of the branchiuran family Argulidae and has a worldwide distribution, causing major economic impacts for freshwater aquacultured fish species worldwide. In the UK, it has economic impacts for both aquaculture and sports fishing industries. Previous studies observed haemorrhagic and inflammatory responses after Argulus infection, which has been taken to support the idea that the parasite secretes chemicals during the feeding process to assist with the ingestion of blood and epithelial tissue. The present study suggests that the blood-feeding ectoparasite of fish, A. foliaceus, may use similar mechanisms for evading host immune responses to those used by sea lice and other haematophagous arthropods. No previous studies have directly investigated the nature of the bioactive compounds / proteins, assumed to be released from these ectoparasites, and which are considered to contribute to feeding processes and host-parasite interactions during infection. Thus, the work described in this thesis was undertaken with the objective of identifying, describing and characterising the secretory components that have previously been suggested to be secreted from glandular cells associated with the feeding appendages of Argulus foliaceus. The current study applied transcriptomic and proteomic techniques in conjunction with in situ methods to investigate known immunomodulatory genes that may serve a function in parasite-host interactions. Overall, the findings of this project have generated considerable additional knowledge concerning the biology of Argulus spp. and have provided a list of proteins that may be used by the parasite to facilitate feeding processes by secreting these active molecules into the host and hence modulating their immune defence mechanisms. This information can be used as a baseline for developing freshwater lice control strategies to help prevent the spread of Argulosis in aquaculture by applying vaccination as means of control using the candidate antigens described in this study to specifically target Argulus spp. Knowledge generated by the work described in this thesis can also contribute to the development of drugs for controlling Argulus or functional components of feed that may serve to protect fish against this parasite. Furthermore, data from this thesis enhances the knowledge of the distribution of toxin/venom or venom-like substances in crustaceans and arthropods in general.

Largespot pompano, Trachinotus botla, is a surf zone carangid with a cosmopolitan distribution in subtropical and tropical waters. Within South Africa, the species occurs along the KwaZulu-Natal coastline where it is a popular recreational fishing target. Recreational fishing in southern Africa has developed significantly in recent years, and is now regarded as an industry with huge economic potential. The long-term contribution of South African recreational fisheries to local economies is reliant upon sustainable exploitation through effective management. Trachinotus botla was found to grow rapidly with maximum observed age of six years. Otolith growth zone deposition was validated using edge analysis. Growth was similar between males and females until ~350 mm FL after which females continued to grow while growth in males slowed. The resulting overall sex ratio was slightly female-biased (1 male: 1.3 females). Trachinotus botla matures early with all fish considered to be mature at 290 mm FL, which corresponds to an age of three years. A protracted spawning season was observed ranging from November to February and there was evidence to suggest that T. botla is a serial spawner. Dietary analysis indicates that T. botla is an opportunistic predator with a catholic diet. The opportunistic utilization of “superabundant” prey items is a fundamental characteristic of the species feeding habits. An ontogenetic dietary shift was observed at approximately 300 mm FL that was linked to a shift in habitat preference. This thesis provided the first evidence that infection by the tongue-replacing isopod, Cymothoa borbonica, reduces the growth rate of wild host fish populations despite not affecting the diet, feeding habits and feeding frequency of their hosts. These results also highlighted the inadequacy of condition factor as a proxy for quantifying the effects of cymothoids on their hosts, and identified the need to incorporate host age when assessing the effects of parasite infection. Information on the life-cycle of C. borbonica, including estimates of the hypothesized “infectious” period and its longevity were obtained through analysis of parasite infection patterns as a function of host age and length. An assessment of the T. botla shore fishery of KwaZulu-Natal using historical catch data revealed that the fishery is stable. Productivity of the T. botla fishery increased towards the north of KwaZulu-Natal. Distinct seasonal variations in the T. botla fishery were also noted with catches peaking in summer months and lowest during winter. A per-recruit assessment revealed that the species is currently underexploited (SBR = 62% of pristine levels), and fishing mortality rate could be doubled before reaching the spawner biomass-per recruit target reference point of FSB₄₀. A combination of the life history characteristics of species, the nature of the recreational shore fishery together with the current management regulation of 5 fish person⁻¹ day⁻¹ has ensured the sustainable utilization of the T. botla resource in KwaZulu-Natal.

Bibliography: leaves 113-144. Investigates the functions of the maternal, protein secretions of the endoparasitoid wasps Venturia canescens Gravenhorst regarding their role in providing protection against the host's immune system. Also investigates mucinous protein secretions on the egg surface and coagulation reactions and their role in protecting eggs against host cellular attacks.

Bibliography: leaves 113-144.
ix, 144 leaves, [56] leaves of plates : ill. (some col.) ; 30 cm.
Investigates the functions of the maternal, protein secretions of the endoparasitoid wasps Venturia canescens Gravenhorst regarding their role in providing protection against the host's immune system. Also investigates mucinous protein secretions on the egg surface and coagulation reactions and their role in protecting eggs against host cellular attacks.
Thesis (Ph.D.)--University of Adelaide, Dept. of Applied & Molecular Ecology, 2002

Some parasites may modify the behavior of their hosts. Altered behaviors may: 1) benefit the host in that they defend against the pathogen, 2) benefit the pathogen and represent manipulations of the host response, and 3) benefit neither the host or the pathogen and simply be a product of the host response to infection. In this thesis I examine four host/parasite systems. For each system, I explore host/parasite behavioral interactions, and examine them with regard to selective pressures that may be acting on both the host and the parasite. I test the Hamilton and Zuk hypothese in 26 species of lizards. I find an inverse relationship between a lizard species' brightness and parasite prevalence. My result lend credence to criticisms of the Hamilton and Zuk Hypothesis. If infection does occur, animals may alter their behavior to impair the growth and reproduction of the parasite. To test this prediction, I examine behavioral thermoregulation in two strains of the snail Biomphalaria glabrata, one resistant to, and one susceptible to, the parasite Schistosoma mansoni. The preferred temperature of infected snails drops five weeks after exposure to the parasite. I propose the hypothesis that pathogen-induced host defense responses result in altered host behaviors and enhanced predation. In particular, I examine the effects of the acute phase response (a physiological response whose symptoms include fever, reduced activity and malaise) on antipredatory behavior in bullfrog (Rana catesbeiana) tadpoles. This host response is associated with the preliminary stages of infection with many pathogens yet its behavioral effects have received little attention. I find that the stereotypical effects of the acute phase response can lead to increased predation. I suggest that altered behaviors may afford some parasites a potential pathway to their next host. I examine the behavioral effects of a yeast, Candida spp., a single-host parasite species in its natural host, the red-legged frog (Rana aurora). Infected tadpoles exhibit the same behavioral modifications that are noted in bacteria injected bullfrog tadpoles. These results suggest that some altered behaviors may occur due to a host response to infection and not due to parasitic manipulation.
Graduation date: 1993

Marburg virus (MARV)–along with Ebola Virus–comprises Filoviridae, a family of virus which causes the life-threatening hemorrhagic fever in human and non-human primates for which there is no clinically approved vaccine. For this reason, this virus can potentially lend itself to pandemic and weapons of bioterrorism. Strikingly, this virus yields asymptomatic responses in its recently discovered host Rousettus aegyptiacus. Understanding of the interaction between MARV and different animal hosts will enable the improved understanding of filovirus immunology and the development of effective therapeutic agents. Although cell lines and primary cells have been used to investigate gene expression analysis of this virus, the transcriptomic view of MARV infection on the tissue samples of animal hosts has been an uncharted territory. The comprehensive analysis of transcriptome in hosts and spillover hosts will shed light on the immune responses on a molecular level and potentially allow the comparative analysis to understand the phenotypical differences. However, there have been gaps in resources necessary to carry the transcriptome research for MARV. For example, MARV host Rousettus aegyptiacus genome and transcriptome had not been available. Furthermore, the statistical machinery necessary to analyze multi-tissue/multi-time data was not available. In this dissertation, I introduce the two items that fill these gaps and show the application of the tools I built for novel biological discovery. In particular, I have built 1) the comprehensive de novo transcriptome reference of Rousettus aegyptiacus and 2) the Multilevel Analysis of Gene Expression (MAGE) pipeline to analyze the RNA-seq data with the complex experimental design. I show the application of MAGE in multi-time, multi-tissue transcriptome data of Macaca mulata infected with MARV. In this study, 15 rhesus macaques were sequentially sacrificed via aerosol exposure to MARV Angola over the course of 9 days, and 3 types of lymph node tissues (tracheobronchial, mesenteric, and inguinal) were extracted from each sample and sequenced for gene expression analysis. With MAGE pipeline, I discovered that the posterior median log2FC of genes separates the samples based on day post infection and viral load. I discovered the set of genes such as CD40LG and TMEM197 with interesting trends over time and how similar and different pathways have been influenced in three lymph nodes. I also identified the biologically meaningful clusters of genes based on the topology-based clustering algorithm known as Mapper. Using the MAGE posterior samples, I also determined the genes that are preferentially expressed in tracheobronchial lymph nodes. In addition to new analysis tools and biological findings, I built the gene expression exploration tool for biologists to examine differential gene expression over time in various immune-related pathways and contributing members of the pathways. In conclusion, I have contributed to the two important components in the transcriptome analysis in MARV research and discovered novel biological insights. The MAGE pipeline is modular and extensible and will be useful for the transcriptome research with the complex experimental designs which are becoming increasingly prevalent with the decrease in the cost of sequencing.

Indiana University-Purdue University Indianapolis (IUPUI)
Vaccinia virus (VV) is the prototypical member of the orthopoxvirus genus of the Poxviridae family, and is currently being evaluated as a vector for vaccine development and cancer cell-targeting therapy. Despite the importance of studying poxvirus effects on the human immune system, reports of the direct interactions between poxviruses and primary human leukocytes (PHLs) are limited. We studied the specific molecular events that determine the VV tropism for major PHL subsets including monocytes, B cells, neutrophils, NK cells, and T cells. We found that VV exhibited an extremely strong bias towards binding and infecting monocytes among PHLs. VV binding strongly co-localized with lipid rafts on the surface of these cell types, even when lipid rafts were relocated to the cell uropods upon cell polarization. In humans, monocytic and professional antigen-presenting cells (APCs) have so far only been reported to exhibit abortive infections with VV. We found that monocyte-derived macrophages (MDMs), including granulocyte macrophage colony-stimulating factor (GM-CSF)-polarized M1 and macrophage colony-stimulating factor (M-CSF)-polarized M2, were permissive to VV replication. The majority of virions produced in MDMs were extracellular enveloped virions (EEV). Visualization of infected MDMs revealed the formation of VV factories, actin tails, virion-associated branching structures and cell linkages, indicating that infected MDMs are able to initiate de novo synthesis of viral DNA and promote virus release. Classical activation of MDMs by LPS plus IFN-γ stimulation caused no effect on VV replication, whereas alternative activation of MDMs by IL-10 or LPS plus IL-1β treatment significantly decreased VV production. The IL-10-mediated suppression of VV replication was largely due to STAT3 activation, as a STAT3 inhibitor restored virus production to levels observed without IL-10 stimulation. In conclusion, our data indicate that PHL subsets express and share VV protein receptors enriched in lipid rafts. We also demonstrate that primary human macrophages are permissive to VV replication. After infection, MDMs produced EEV for long-range dissemination and also form structures associated with virions which may contribute to cell-cell spread.

Mistletoes are a group of hemiparasitic plants that grow on a wide variety of host trees and differ in their degree of host specificity, ranging from specialists to generalists. Mistletoes can also be locally host specific where host preference varies geographically, i.e. at a given location a mistletoe species may infect only part of its overall host set. The mistletoe Agelanthus natalitius parasitises at least 11 tree genera distributed throughout South Africa. However, there is geographic variation in infection patterns over the parasite’s range, suggesting that A. natalitius may be locally host specific. We quantified the degree of host specificity and tested the mechanisms that direct host specialisation in two distinct mistletoe populations at Highover and Mtontwane (about 110 km apart) in KwaZulu-Natal, South Africa. We investigated the distribution, abundance and community composition of woody species that host the mistletoe. We also assessed the effect of light on germination and early survival of the mistletoes in a greenhouse experiment. We conducted field reciprocal transplant experiments at both sites to investigate the compatibility of these mistletoes with their hosts Acacia karroo and A. caffra during early development. We then analysed the nutrient and water contents of the mistletoe-host pairs to investigate the role of nutrient and water status in directing host specificity in mistletoes. We further studied avian dispersal in the field and in captivity to investigate optimal dispersal distance and germination success, and evaluated their role in determining mistletoe host specificity. At both study sites, five host species were recorded as being parasitised by the mistletoe A. natalitius. A. karroo and A. caffra appear to be the two most common host species in the region; both grow abundantly at the study sites and were recorded with high infection by A. natalitius. However, A. karroo is the most abundant host species and the mistletoe showed a high degree of host specificity on A. karroo. Infection by mistletoes was positively correlated with tree size, and was highly aggregated, both individually and locally. Field observations and greenhouse shade experiments showed that light can influence mistletoe distribution. Germination of mistletoe seeds was independent of host species and site. However, hypocotyls (the structures that develop into haustoria) grew longer when placed on their source host species within their locality. Additionally, they showed preference for the most abundant host species, A. karroo. Water and nutrient status of the host species A. karroo and A. caffra had no significant effect. Thus, host nutrient and water content may not account for host specificity in this mistletoe species. Mistletoes accumulated more nutrients and maintained more negative than their host trees. We also investigated the mistletoes’ use of passive nutrient uptake (from host xylem) and active nutrient uptake (from host phloem) by using the N:Ca ratio as an index of nutrient access. Mistletoes growing on A. caffra had a ratio > 1, i.e. the mistletoe actively accessed nutrients from the phloem of host trees. However, mistletoes on A. karroo had a N:Ca ratio < 1, which implies that they passively accessed nutrients from the xylem. The difference in mechanism of nutrient acquisition on different host species may reflect the level of compatibility between mistletoe and host. Several bird species were frequently observed to feed on mistletoes, many of which were used in our captivity studies. Although birds did not consume mistletoe fruits in captivity as they do in the field, they were effective in removing the pulp cover of mistletoe fruits and exposing seeds in germinable condition. In captivity, the Red-winged Starling ingested whole fruits and regurgitated seeds, deliberately wiping their bills on twigs to remove the sticky seeds. As a result, germination success of mistletoes processed by Red-winged Starlings was higher than any other bird species tested in captivity. Overall, there appears to be host specificity in morphologically identical mistletoes. Understanding the mechanisms that result in host race evolution are potentially important to the process of speciation in hemiparasitic mistletoes. We need to take into account genotypic matching in conserving these different forms of mistletoes and their host Acacia genotypes. Further research into the mechanisms of host specificity and patterns of genotypic matching is warranted.
Thesis (M.Sc.)-University of KwaZulu-Natal, Pietermaritzburg, 2009.

Bibliography: leaves 82-111. This thesis analyses the molecular composition of the surface components of the Endoparasitoid "Venturia canescens" using serological methods and specific sugar-binding lectins as diagnostic tools. The data reveals that the protective layer consists of at least two parts: a mucin-like glycoprotein and additional components from the wasp calyx fluid and the host hemolymph. The study suggests that the wasp larval cuticle is protected in a similar fashion to the egg chorion, except that the calyx-specific VLPs are probably replaced on the larval cuticle by host hemolymph proteins. The findings suggest that the mechanism of passive immune evasion could emerge during the evolution of the wasp-host interactions. The implication is that structurally conserved components may have similar functions in the parasitic and non parasitic species and could constitute a useful pre-adaptations for an endoparasitoid lifestyle.

Ceratomyxa shasta infects salmonids in the Pacific Northwest (PNW) of North America, occasionally causing losses in wild and captive populations. Host-specific parasite genotypes (O, I, II, III) were previously characterized molecularly using markers in the ribosomal DNA and phenotypically by type host in the Klamath River, CA/OR. This thesis sough to re-examine the composition of the parasite population elsewhere in the PNW and to further evaluate the host specificity of each genotype. I surveyed salmonids native to the PNW primarily from the Fraser, the Columbia and the Sacramento River basins. I also conducted sentinel studies on the Willamette and Deschutes Rivers that exposed native and non-native salmonids to parasite populations above and below migration barriers. These studies expanded upon the known host range of each genotype: O was specific to rainbow/steelhead (Oncorhynchus mykiss) and coastal cutthroat trout (O. clarkii); I was specific with Chinook salmon (O. tshawytscha); II was non-specific, being detected in six species, but predominating in coho (O. kitsuch), chum (O. keta), and pink (O. gorbuscha) salmon; and III was also non-specific infecting many native and non-native salmonids. Hosts infected with genotype III were considered “adequate” if myxospore development occurred, and included brook char (Salvelinus fontinalis), brown (Salmo trutta), rainbow, cutthroat, and steelhead trout; but Chinook, kokanee/sockeye (O. nerka) and Atlantic salmon (Salmon salar) were less suitable. The distribution, life history, and phylogenetic traits of each salmonid host are factors that potentially explain the host specificity and the spatial and temporal patterns of each genotype. Data collected in this thesis provide evidence that host-specific C. shasta coevolved with Pacific salmonids, adapting unique host-parasite relationships over time.
Graduation date: 2012