Thesis (M. Phil.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Thesis (M. P. A.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

<p>Avian Influenza (AI) is a contagious viral zoonotic disease with great public health implications and negative socioeconomic impact (WHO, 2006a). The highly pathogenic avian influenza (HPAI) infection is transmitted from birds to man mostly through contact with contaminated poultry and objects (INFOSAN, 2005), hence people who come in contact with birds such as live bird sellers (LBS) are the more vulnerable population (WHO, 2006a). Inadequate knowledge of AI health risks and poor practice of AI preventive measures amongst LBS increases the risk of spread of the infection in both humans and animals.The aim of this study was to describe and quantify the knowledge and practice of LBS with regards to avian influenza health risks and preventive activities in Agege, an urban area in Lagos State, Nigeria.</p>

A proper vaccination program can play a critical role in prevention and control of avian influenza (AI) in commercial poultry. Low pathogenic avian influenza viruses (LPAIV) of H5 and H7 AI subtypes cause serious economic losses to the poultry industry and have the potential to mutate to highly pathogenic AI (HPAI) strains. Due to trade implications, differentiation of infected from vaccinated animals (DIVA) is an important issue in the control of AI. Therefore, the development and characterization of vaccine candidates with DIVA properties is critical in improving vaccination programs. Keeping these aspects in mind, we investigated the role of an NS1 mutant virus as a potential live attenuated DIVA vaccine. The NS1 protein of influenza virus plays a major role in blocking the host's antiviral response. Using an eight-plasmid reverse genetics system, we recovered the low pathogenic parental (H5N3) and NS1 mutant (H5N3/NS1/144) viruses. H5N3/NS1/144 expresses only the first 144 amino acids of the NS1 protein compared to the 230 of the parental H5N3. The growth properties of H5N3 and H5N3/NS1/144 were compared in cell culture and in different age embryonated chicken eggs. Our results confirmed that NS1 is involved in down regulation of interferon as shown by IFN-beta mRNA expression analysis and by the inability of H5N3/NS1-144 to efficiently grow in older age, interferon competent, chicken embryos. However with regards to safety the virus reverted to virulence within five back passages in chickens and was therefore not a safe vaccine candidate. However the killed form of H5N3/NS1-144 was a safer alternative and it also induced antibody titers and protection not significantly different from the parental H5N3 as vaccine. To further understand the reversion of H5N3/NS1/144 to virulence, we carried out 3 independent serial passages of H5N3/NS1/144 in increasing age of embryonated chicken eggs and examined the NS1 gene for presence of mutations. RT-PCR and sequence analysis of the NS gene in all three lineages showed the presence of a 54 amino acid deletion resulting in the generation of a 87 amino acids long NS1 ORF with a point mutation (L80V) at the site of deletion. In addition, the NS1 ORF in lineages L2 and L3 presented two additional point mutations in the RNA binding domain (Q40R and T73M). To determine if these mutations played a role in increased virulence, recombinant viruses expressing these mutant NS1 proteins in the background of parental virus were generated by reverse genetics and their replication properties and pathogenicity was examined in vitro, in ovo and in vivo systems. Our results showed that the 87 amino acid long NS1 protein clearly increased virus replication and virulence specifically in interferon competent systems. In addition, the two point mutations in the RNA binding domain of NS1 ORF expressing 87 a protein slightly increased the virus virulence. Overall this study reinforces the role of NS1 in influenza virus pathogenicity and supports the use of killed inactivated NS1 mutant virus vaccines as potential DIVA vaccines.

Avian influenza virus (AIV) is a type A virus of the family Orthomyxoviridae and its outbreaks not only cause economic losses in poultry, but also are worldwide threats to human health. The phenotypic changes in host cells induced by pathogens are always accompanied by remarkable changes in gene expression. Therefore understanding the gene expression profile of infected cells at the global level is important to get insights into interactions between hosts and viruses. Different genomic approaches have been utilized in the current study to investigate the host-AIV interactions in chickens. The Ser to Asn mutation on position 631 in the chicken Mx1 protein was reported to result in a positive antiviral function in vitro. With AIV infection, the Mx1 mRNA expression levels in heterozygous birds were significantly up-regulated. Additional mutations on the chicken Mx1 coding region were identified by sequencing. The results showed that most identified mutations were co-segregated with S631N mutation except one insertion in the position of 1544bp in the heterozygous birds. We speculate this insertion might be related to the up-regulation of mRNA expression of heterozygous birds with AIV infection. The miRNAs play critical roles in biological processes and are important effectors in host-pathogen interactions. The miRNA deep sequencing was used to profile miRNAs in AIV infected or non-infected chickens. Differentially expressed miRNAs identified have expanded our knowledge in the functions of these potential immune related chicken miRNAs regulating host response to AIV infection. Both microarray and transcriptome analysis by RNA-Seq were used in the current study to investigate the global gene expression of host response to AIV infection. Through the comprehensive analysis, a list of strong candidate miRNAs such as miR-32 and their host target genes including Mx1 were identified for further elucidating the regulatory mechanism of host-AIV interaction. In summary, we have identified many important candidate host genes and miRNAs which play important roles in the modulation of host response to AIV infection using genomic approaches. Further investigation of underline regulatory mechanisms of these genes, miRNAs or related pathways, followed by functional analysis, could lay solid foundation for understanding cellular and molecular mechanisms of the host-AIV interactions, thereby, pave a way for the development of novel protective strategies against AIV infection in chickens.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 174-194). Also available online.

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 169-186). Also available in print.

Thesis (Ph. D.)--University of Hong Kong, 2010. / Includes bibliographical references (leaves 169-186). Also available online.

Thesis (Ph. D.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 174-194). Also available in print.

published_or_final_version / Microbiology / Master / Master of Philosophy