Thesis (Ph. D.)--University of Texas at Austin, 2002. / Vita. Includes bibliographical references. Available also from UMI Company.

Thesis (Ph. D.)--Florida State University, 2003. / Advisor: Dr. Michael S. Chapman, Florida State University, College of Arts and Sciences, Institute of Molecular Biophysics. Title and description from dissertation home page (viewed Mar. 11, 2004). Includes bibliographical references.

Thesis (M. Phil.)--University of Hong Kong, 2002. / Includes bibliographical references (leaves 116-132).

published_or_final_version / Microbiology / Doctoral / Doctor of Philosophy

published_or_final_version / Microbiology / Doctoral / Doctor of Philosophy

Dengue is the most common mosquito-borne human disease, leading to 2.5 billion people at risk, 50-100 millions infections each year worldwide and among them, 500 000 severe dengue cases (dengue hemorrhagic fever, DHF/ dengue shock syndrome, DSS) plus more than 20 000 deaths. It can be caused by any of four dengue virus serotypes, which are antigenicly distinct and belong to the Flaviviridae family, genus Flavivirus. However, up till now there is no specific drug and vaccine against dengue. Understanding mechanisms developed by dengue virus to exploit host cells during all stages of the replication cycle is a first step towards the rationale design of anti-viral strategies. Very little is known about the late stages, which consist of assembly, budding and secretion of the virus. It is therefore very important to develop tools in order to study the egress of the virus. In this study, I investigated a stable cell line named Hela-prME that expresses serotype 1 dengue virus (DENV-1) prM and E native structural envelope proteins and constitutively produces dengue recombinant subviral particles (RSPs). Biochemical characterization of DENV-1 RSPs has validated that this cell line is a potential tool to study the dengue viral late-stage. Indeed, the maturation process observed with RSPs is similar to the pathway described for real virus (cleavage of prM fragment, homodimerization of E, acquisition of complex sugars). To better understand and depict the dengue virus late-stage secretion, I combined various electron microscopy (EM) techniques e.g. classical transmission electron microscopy (TEM), negative staining, immunogold labeling on cryo-ultrathin sections (Tokuyashu method) and tomography (ET) with such RSPs tool. The EM results obtained illustrate that electron dense particles and tubules labeled by antibodies directed against E and prM proteins were abundantly found in the lumen of endoplasmic reticulum (ER)-related cisternae of HeLa prME cells. Epositive particles were also found in other structures such as Golgi stacks and vesicles nearby as well as in aggregates with electron dense materials inside and surrounded by membrane. These particles are most likely corresponding to DENV-1 RSPs whereas the tubules may be other structures induced by assembly of prM and E proteins. This study has clearly shown that DENV-1 RSPs assemble in the ER and transport through the secretory pathway before being released. This work further validates the use of dengue RSPs and RSPs-producing cells as a model to study viral egress. / published_or_final_version / Pathology / Master / Master of Philosophy

Influenza B virus contributes to a significant portion of influenza disease burden in men. It is structurally similar and replicates in the same manner as the influenza A virus, leading to a comparable clinical presentation between the two viral species. Since 1977, influenza B has caused seasonal epidemics around the world together with A/H1N1 and A/H3N2 subtypes, and has a strong affinity to affect children of school age and young adults. In the 1980s, two antigenically distinct lineages of influenza B virus emerged, one being the B/Yamagata lineage and the other known as B/Victoria lineage. The most significant antigenic difference between the two is located in the HA1 domain of the viral hemagglutinin. Host immunity is not shared between the two viral lineages. Therefore, the global prevalence of the two influenza B lineages is closely monitored by the World Health Organization in order to decide which viral lineage to include in the annual trivalent influenza vaccines. Surprisingly, the current methods used in influenza B viral surveillance and lineage discrimination have not seen much technical advancement in nearly 25 years since the emergence of two viral lineages. The current study presents a novel, asymmetric real-time PCR assay which is able to determine the viral lineage in addition to detecting the presence of influenza B virus in clinical specimens. Asymmetric PCR is performed by deliberately limiting the amount of primers in one side of a PCR reaction. This significantly affects the replication efficiency and sensitivity of the PCR reaction, but at the same time facilitates target sequence detection by hybridization probes, due to an increased number of single stranded products in the reaction. Nevertheless, the use of asymmetric PCR has been avoided in the past. The recent introduction of linear-after-the-exponential (LATE) PCR refines the method by adjusting melting temperature of PCR primers so that TmLimiting – TmExcess ≥ 0°C. The modification is shown to raise the efficiency of asymmetric PCR to those of symmetric PCR, as well as allowing more relaxed criteria for PCR primer and probe design. In the current asymmetric assay, pan-influenza B primers and probes targeting Victoria and Yamagata linage specific regions of the influenza B HA were evaluated against a similar symmetric influenza B assay published by the World Health Organization. HA plasmid standards and 155 clinical specimens were tested by both assays, in which the two had intra-assay CV% of less than 5%. Albeit the efficiency and sensitivity of WHO published assay was slightly higher, LATE-PCR based assay performed influenza B detection and genotyping simultaneously with the use of hydrolysis probes. The overall sensitivity/ specificity of the genotyping assay are 96.81%/100% while the WHO recommended assay is at 98.94%/100% for influenza B detection. The LATE-PCR based genotyping assay also successfully genotyped 89 out of 94 clinical specimens. In conclusion, the influenza B genotyping assay evaluated in this study performed favorably and could serve as an alternative to cumbersome viral culture methods to aid in high-throughput global influenza surveillance. / published_or_final_version / Microbiology / Master / Master of Medical Sciences

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