Hepatitis B virus (HBV) is hyperendemic to southern Africa, the Asia-Pacific region, and the Amazon Basin. HBV causes both acute, and chronic infection of the liver that result in a wide spectrum of liver diseases ranging from acute mild subclinical infection, and an asymptomatic carrier state (ASC) to severe clinical manifestations, including, severe acute and, chronic hepatitis, which can progress to cirrhosis, and the development of hepatocellular carcinoma (HCC). Several viral factors have been implicated in the activation, and inhibition of apoptosis. The development, and progression of this wide spectrum of liver diseases are associated with an unregulated increase or decrease in hepatocyte apoptosis as well as a loss of balance between cell proliferation, and apoptosis. In southern Africa, genotype A of HBV is the predominant genotype, with subgenotype A1 prevailing. Individuals infected with subgenotype A1 have several unique characteristics, including relatively lower levels of HBV DNA, and early seroconversion of hepatitis B e antigen (HBeAg) to antibodies against HBeAg during the course of HBV infection. Infection with this subgenotype is associated with rapid disease progression, and high frequency of HCC development. Moreover, patients infected with subgenotype A1 had increased levels of apoptosis when compared to the other subgenotypes. The G1862T mutation occurs most frequently in subgenotype A1. In the clinical setting, South African HCC patients infected with G1862T subgenotype A1 strains had higher levels of apoptosis while ASCs patients infected with G1862T subgenotype A1 strains had lower levels of apoptosis, when compared to those infected with wild-type. To date, G1862T has been functionally characterized in subgenotype A2, genotype B and in a genotype D HBV genome containing a subgenotype A1 precore (PreC) region. The objectives of our study were to construct 1.28 mer replication competent clones containing an endogenous HBV promoter for wild-type subgenotypes A1, A2, and D3 as well as mutant G1862T subgenotype A1, and to functionally characterize these strains in tissue culture. Transfection of Huh7 cells was used to follow the viral replication, expression of HBeAg, activation of the unfolded protein response (UPR), and subsequent apoptosis. The strategy used for the generation of these replication competent clones had several advantages. Very few PCR errors were introduced, and carry-over of enzymes, nonspecific products, and reaction reagents downstream was prevented. The clones contained endogenous HBV promoters, and enhancers, and were generated from a single complete genome of HBV. These replication competent clones may be used in future studies for the establishment of stable cell lines that constitutively express HBV proteins without the need for further manipulation. This strategy can be used for the generation of replication competent clones belonging to genotypes A to D, and G, and with a few minor modifications, for genotypes E, F, and H. Using the newly generated clones, their replication competence was demonstrated using transfection of Huh7 cells. Even in the absence of an exogenous promoter, these clones were able to support the expression of intracellular, and extracellular HBV DNA at levels of 108 to 109 genome copies/ml. HBcAg, HBeAg, and HBsAg were expressed for a period of five days, and the order of expression was similar to that seen during acute HBV infection. Comparison of transfection with a replication competent clone containing an exogenous HBV promoter demonstrated higher expression of HBV DNA, and proteins, as well as an earlier expression, and accumulation of HBeAg in the endoplasmic reticulum (ER) relative to the clone containing an endogenous HBV promoter. This initial increased accumulation of HBeAg in the ER did not affect the level of activation of the UPR, but led to an increased level of total cell death as a consequence of necrosis. When comparing the different subgenotypes following transfection into Huh7 cells, subgenotype D3 replicated at a lower level, as measured by HBsAg, and HBV DNA levels, with HBeAg passing through the secretory pathway earlier, when compared to cells transfected with genotype A. There was no difference in the intracellular, and extracellular HBsAg between cells transfected with either subgenotype A1 or A2. However, cells transfected with subgenotype A1 had higher levels of intracellular replicative intermediates, HBeAg, and HBcAg, and lower extracellular expression of HBeAg from days 1 to 3, when compared to cells transfected with subgenotype A2. The intracellular retention of the PreC/ core (C) precursor protein in cells transfected with subgenotype A1 was clearly demonstrated by its lower expression in the secretory pathway, and its higher co-localization in the nucleus, using indirect immunofluorescence. This intracellular retention led to greater ER stress, and an earlier, and prolonged activation of the UPR. This correlated well with the higher PERK, ATF6, and IRE1/XBP1 activity seen on days 3 than on day 5. These findings suggest that the prolonged activation of the UPR in cells transfected with subgenotype A1 led to increased apoptosis, and subsequent induction of liver damage, and may therefore, be a contributing factor to the higher hepatocarcinogenic potential of subgenotype A1. Our study demonstrated that G1862T reduced replication, and led to the initial temporal retardation of intracellular core-particle-associated HBV DNA. Although, G1862T did not affect HBsAg expression, it led to a decreased expression of HBcAg, and HBeAg. The decreased expression of extracellular HBeAg was probably as a result of decreased cleavage efficiency by the signal peptide, which consequently led to the retardation of the PreC/C precursor protein in the ER, and ER-Golgi intermediate compartment (ERGIC), and its decreased expression in the nucleus. This retardation, and accumulation led to the earlier activation of all three UPR pathways, but not to increased apoptosis. Therefore, it is evident that G1862T does not completely abolish HBeAg expression, but affects the rate of HBeAg maturation, and its expression through the secretory pathway. These findings suggest that in response to the accumulation of HBeAg in the ER, the UPR was activated resulting in the alteration of the capacity to overcome this stress, consequently leading to a new homeostasis of the ER being reached. The capacity of the ER is increased, with no further activation of the UPR and apoptosis, which facilitates maturation of HBeAg. In conclusion, our study for the first time demonstrated that there are a number of factors that influence the expression of proteins in HBV transfection studies including the type of transcriptional promoter, the different genotypes/subgenotypes of HBV, the use of protein expressing as opposed to replication competent clones, and the presence, and absence of mutations, such as the G1862T. Therefore, when comparing the outcomes of various experiments these factors should be taken into consideration, and the results interpreted with caution, because experiments may not be strictly speaking comparable. Importantly, replication competent clones were generated from strains circulating in southern Africa. The generation of these clones is an important step in further functional characterization of African strains of HBV, and their comparison to strains circulating other geographical regions of the world. These strains, in particular, subgenotype A1 can develop unique mutations, such as the G1862T, which we demonstrated can influence the expression of HBeAg, in a way that it can possibly account for the higher hepatocarcinogenic potential of subgenotype A1.

Thesis (MPH)--University of Limpopo, 2009. / BACKGROUND AND AIM: Hepatitis B virus (HBV) is the major cause of hepatitis in South Africa (SA), with an estimated 4 million carriers. It is transmitted by infected blood and other body fluids, placing health care workers (HCWs) at high risk of infection. The SA Department of Health strongly recommends that all HCWs be vaccinated against HBV, but studies have shown that uptake of the vaccine is sub-optimal. This study aimed to estimate HB vaccination coverage levels among nurses, and describe the demographics and characteristics of the HB vaccination policies associated with different levels of coverage, at private and public hospitals in Tshwane. METHODS: This was a questionnaire-based cross-sectional study on 300 randomly selected nurses and 12 chief infection control officers (CICOs) from 13 hospitals (6 public and 7 private) in Tshwane performing high risk procedures. CICOs were asked questions about HB vaccination policies and coverage, while nurses were asked about demographics, HB vaccination status, and the HB vaccination policies of their institutions. RESULTS: The response rate was 84.3% (253/300) for nurses, and 75% (9/12) for CICOs. Of the nurses, 68.0% (172/253) were vaccinated, and logistic regression analysis found that those statistically significantly most likely to be vaccinated were: 30 years and younger (odds ratio [OR]=2.9; 95% CI: 1.11–7.59); employed in private hospitals (OR=3.0; 95% CI: 1.24–7.32); and graduated after 1990 (OR=2.6; 95% CI: 1.10–6.19). Also, logistic regression analysis found two statistically significant policy-related predictor for vaccination uptake, which was the presence of HB vaccination program (OR=4.6; 95% CI: 2.11-10.06); and compulsory HB vaccination (OR=2.8; 95% CI: 1.37-5.70. CONCLUSION: There is a need for a national policy on HB vaccination of HCWs which should include compulsory vaccination, to increase the vaccination coverage level amongst nurses.

Thesis (MSc. (Medical Virology))-- University of Limpopo, 2011. / Introduction: Sub-Saharan Africa is a region with hepatitis B virus (HBV) hyperendemicity with more than 8% HBsAg prevalence. An estimate of two billion people has been reported to carry HBV markers. HBV was associated with about 25% of annual deaths in Africa. HBV possesses a DNA polymerase which lacks proofreading mechanism. This results in highly variability and genetic diversity which poses a challenge for the diagnosis and therapeutic management of HBV infection. High mutation rate of HBV also has great implications on the development of drug resistant mutations. Moreover, HBV diversity represents a challenge for the sensitivity of immunological and molecular diagnostic assays. A number of studies on HBV full length genome have been conducted particularly in developed countries. Limited studies are available in Africa and South Africa. In South Africa, few studies have been done analysing the complete genome of HBV isolates from patients with asymptomatic carriers and fulminant hepatitis B (Owideru et ai, 2001 a; Owideru et ai, 2001 b; Kimbi et ai, 2004; Kramvis et ai, 2002).This study was aimed at characterising the full-length genome of HBV isolates at Dr George Mukhari Hospital, Pretoria, South Africa, with a view of developing a PCR-based technology for amplification and characterisation of HBV strains with different serological profiles. The technology, if successfully developed, will contribute in understanding the molecular mechanisms resulting in various HBV variants or isolates. Methods: The study design was exploratory. Four stored serum samples collected from HBV infected patients at Dr George Mukhari hospital, Pretoria, were used to develop the molecular technology and test the hypothesis. HBV serology was previously performed targeting 5 HBV serological markers; HBsAg, anti-HBs, anti-HBc, HBeAg and anti-HBe using Elecsys version; HBV DNA quantification was done using Cobas Amplicor HBV DNA monitor assay, HBV DNA was extracted and subjected to nested PCR assay targeting HBV full length genome as two overlapping fragments: fragment A (1670 bp) and fragment B (1868 bp). The generated PCR products for both fragments were cloned into the pGEM T easy vector and 2 clones were selected from each sample. The plasm ids were purified using Invisorb@ Spin Plasmid Mini Two and the clones were recovered by PCR assay. The sample PCR products and the clone PCR products were purified and sequenced using SpectruMedix SCE2410 genetic analysis system. HBV genotyping was performed using the NCBI web-based genotyping tool. Phylogenetic analysis was done using MEGA 4 software to confirm HBV genotypes. Results: Serology results were as follows: All samples were HBsAg positive, Anti-HBs negative, anti-HBc positive and anti-HBe negative. Sample B1121 and sample 6 were HBeAg positive while samples B452 and 5 were HBeAg negative. A total of 12 PCR products were sequenced (4 study samples and 8 clones [2 clones each sample]). In total, 7 HBV full length genome sequences were deduced from this study, with 3 sequences belonging to genotype A, 2 to genotype C and 2 to genotype D. 3 HBV genotypes were detected from this study; genotype A, C and D with subgenotype A2, C1 and D1 respectively. Mutations were observed throughout the genome. In the pre-S/S open reading frame (ORF), the most significant findings were the detection of mutations within the "a" determinant site and major hydrophilic region (MHR). These mutations included Y161F,E164G observed in sample B1121 and B1121C1 belonging to subtype A1; 2 amino acid insertion at aa 161-162 in sample 5 belonging to subtype C1. Drug resistance associated mutations were identified in the polymerase gene, these included M204T and L217R which are associated with adefovir resistance, M204T also resulted in a change from tryptophan (W) to arginine (R) at aa 196 on the overlapping surface gene on sample B452 C1. Basal core promoter (BCP) and pre core/core mutations were detected in study isolates; specifically the BCP double mutation (1762/1764) was seen in 8 isolates which belonged to subtype C1 (5) and D1 (3) and the pre-core stop codon mutations (G1896A) in 4 isolates. (2 belonging to subtype C1 and the other 2 to D1). Other changes observed included a 48 nucleotides deletion in the pre-core gene, 6 nucleotides insertion in the HBx gene of all subtype D1 isolates and a 3 nucleotides deletion in subtype C1 clone. Conclusion: This study successfully optimised a PCR-based technology for the amplification and characterisation of HBV full length genome. 3 HBV genotypes were detected with subtypes A2, C1 and D1. However, the detected subtypes are rarely detected in South Africa. The detection of subtype A2 may confirm its Southern African origin. Drug resistance associated mutations were observed in this study. These included the adefovir resistance mutation which the current study confirmed it is a naturally occurring mutation as it was detected in adefovir therapy na'ive patient. The BCP and pre-core/core mutations were detected in genotype C and D isolates; however, their association with serological profile and clinical outcomes could not be deduced. Unique or novel mutations were seen in the study isolates, these included 48 nucleotides deletion in the pre core gene, 3 amino acids insertion in the RNase H and 8 amino acids deletion in the RT domain of polymerase gene. To our knowledge, these mutations have not been identified or reported in the literature. The detection of 6 nucleotide insertion in the HBx gene was reported for the first time in South African isolates. Further analysis is required to ascertain the biological significance of the unique mutations detected in this study.

Thesis ( M Med ( Virology ) )-- University of Limpopo (Medunsa Campus), 2013. / Introduction: The hepatitis B virus (HBV) causes a serious type of liver disease referred to as hepatitis B, which is associated with various fatal sequelae following the onset of chronic infection. As a result of the global burden of chronic HBV infection, HBV-related mortality is currently estimated at 620 000 annual deaths worldwide (Hwang and Cheung, 2011). The World Health Assembly (WHA) recommended in 1992 that the hepatitis B vaccine be incorporated into national immunization programmes universally, especially in the hyperendemic regions of the world, in order to curb the global burden of hepatitis B (WHO, 1992). Accordingly, South Africa introduced the hepatitis B vaccine into the national Expanded Programme on Immunization (EPI-SA) in April 1995. Almost 17 years later, South Africa has not conducted any nationwide serosurveys to monitor the population impact of the hepatitis B vaccine. Instead, a number of field and laboratory studies have been conducted only in vaccinated children within the first 5 years of life and as such reports on the short¬term impact made by the hepatitis B vaccine in the country have largely relied on these studies (Tsebe et al., 2001; Schoub et al., 2002; Simani et al., 2008). The aim of the current study therefore was to assess the population impact made by the hepatitis B vaccine post its introduction into EPI-SA using an age stratified, cross-sectional study. The objectives were to compare the prevalence of HBV exposure between the post- and pre-vaccination populations of South Africa, determine the influence of HIV infection on the prevalence of HBV exposure between the post- and pre-vaccination populations of South Africa by performing a subset analyses, and lastly, to perform molecular characterization of hepatitis B surface and polymerase genes in HBV DNA positive individuals. Materials and Methods: This was an explorative and descriptive retrospective, cross¬ sectional study based on recently tested and stored blood samples from the NHLS fi Diagnostic Laboratory in the Department of Virology. For the purpose of this study, these samples were obtained after Ethics approval, and two target populations identified based on the year (Le. 1995) the hepatitis B vaccine was introduced into EPI-SA; a post-vaccination population consisting of 605 blood samples from individuals aged 1-15 years and a pre¬vaccination population consisting of 601 blood samples from individuals aged 16-25 years. The post-vaccination population was further stratified by age as follows; 1-5,6-10 and 11-15 years, in order to assess immunity and chronic carriage of HBV across the different age groups. All samples were tested for the following primary serological markers; HBsAg, anti¬HBc and anti-HBs, to determine the prevalence of HBV chronic carriage, past HBV exposure and immunity to HBV infection respectively. Samples were further assessed for the vi incidence of acute HBV infection by testing for IgM anti-HBc. All serological testing was performed using the Elecsys@ 2010 Immunoassay System. Samples with serological evidence of infection or exposure to HBV were selected and screened for HBV DNA using a real time PCR assay to determine the prevalence of active HBV infection within this group. Study subjects with records of their HIV status, either positive or negative, were also pooled for subset analyses in order to determine the influence of HIV infection on immunity and chronic carriage of HBV. Finally, samples positive for HBV DNA were subjected to molecular characterization of the hepatitis B surface (S) and polymerase (pol) genes. Results: Following serological screening, immunity to HBV infection was found to be significantly (p<0.001) higher (56.7%) in the post-vaccination population than in the pre-vaccination population (15.5%). Within the post-vaccination population alone, immunity was found to wane with increasing age from 76.1 % in those 1-5 years of age to 50.0% in those 6-10 years and 44.2% in those 11-15 years of age. Chronic carriage on the other hand was significantly (p=0.008) reduced in the post-vaccination population with 1.5% HBsAg prevalence as compared to 4.0% in the pre-vaccination population. Within the different age strata, chronic carriage increased with increasing age (0.5% in 1-5 years; 1.3% in 6-10 years; 2.5% in 11-15 years). Overall, no acute HBV infection was detected within the post-vaccination population, while a 14.6% prevalence rate of acute HBV infection was found for the pre-vaccination population. From the subset analyses, immunity was found to be significantly (p<0.001) higher in the HIV uninfected population as compared to the HIV infected population; 82.5% versus 22.0% in the post-vaccination population and 26.7% versus 0% in the pre-vaccination population, while chronic carriage was found to be higher in the HIV infected population than in the HIV uninfected population. Following molecular characterization of the HBV S gene, it was revealed that the majority of the viral isolates were genotype A, with only 1 genotype D isolate found. A number of notable amino acid i$ variations were also detected within the antigenic region of the HBsAg of viral isolates, inCluding the K122R, N131T, T143S, and E164D mutations. Conclusion: Introduction of the hepatitis B vaccine into EPI-SA has shown remarkable success in children under the age of 5 years. Overall, immunity and chronic carriage of HBV within the post-vaccination population has been greatly impacted by hepatitis B immunization. Within the HIV infected population, susceptibility to HBV infection remains a cause for concern. Finally, although amino acid variations within the viral HBsAg are present, vaccine escape-related mutants appear to be rare or even absent within the South African population. vii

Thesis (M Med (Virology))-- University of Limpopo (Medunsa Campus), 2013 / Introduction: The hepatitis B virus (HBV) causes a serious type of liver disease referred to as hepatitis B, which is associated with various fatal sequelae following the onset of chronic infection. As a result of the global burden of chronic HBV infection, HBV-related mortality is currently estimated at 620 000 annual deaths worldwide (Hwang and Cheung, 2011). The World Health Assembly (WHA) recommended in 1992 that the hepatitis B vaccine be incorporated into national immunization programmes universally, especially in the hyperendemic regions of the world, in order to curb the global burden of hepatitis B (WHO, 1992). Accordingly, South Africa introduced the hepatitis B vaccine into the national Expanded Programme on Immunization (EPI-SA) in April 1995. Almost 17 years later, South Africa has not conducted any nationwide serosurveys to monitor the population impact of the hepatitis B vaccine. Instead, a number of field and laboratory studies have been conducted only in vaccinated children within the first 5 years of life and as such reports on the short¬term impact made by the hepatitis B vaccine in the country have largely relied on these studies (Tsebe et al., 2001; Schoub et al., 2002; Simani et al., 2008). The aim of the current study therefore was to assess the population impact made by the hepatitis B vaccine post its introduction into EPI-SA using an age stratified, cross-sectional study. The objectives were to compare the prevalence of HBV exposure between the post- and pre-vaccination populations of South Africa, determine the influence of HIV infection on the prevalence of HBV exposure between the post- and pre-vaccination populations of South Africa by performing a subset analyses, and lastly, to perform molecular characterization of hepatitis B surface and polymerase genes in HBV DNA positive individuals. Materials and Methods: This was an explorative and descriptive retrospective, cross¬ sectional study based on recently tested and stored blood samples from the NHLS fi Diagnostic Laboratory in the Department of Virology. For the purpose of this study, these samples were obtained after Ethics approval, and two target populations identified based on the year (Le. 1995) the hepatitis B vaccine was introduced into EPI-SA; a post-vaccination population consisting of 605 blood samples from individuals aged 1-15 years and a pre¬vaccination population consisting of 601 blood samples from individuals aged 16-25 years. The post-vaccination population was further stratified by age as follows; 1-5,6-10 and 11-15 years, in order to assess immunity and chronic carriage of HBV across the different age groups. All samples were tested for the following primary serological markers; HBsAg, anti¬HBc and anti-HBs, to determine the prevalence of HBV chronic carriage, past HBV exposure and immunity to HBV infection respectively. Samples were further assessed for the vi incidence of acute HBV infection by testing for IgM anti-HBc. All serological testing was performed using the Elecsys@ 2010 Immunoassay System. Samples with serological evidence of infection or exposure to HBV were selected and screened for HBV DNA using a real time PCR assay to determine the prevalence of active HBV infection within this group. Study subjects with records of their HIV status, either positive or negative, were also pooled for subset analyses in order to determine the influence of HIV infection on immunity and chronic carriage of HBV. Finally, samples positive for HBV DNA were subjected to molecular characterization of the hepatitis B surface (S) and polymerase (pol) genes. Results: Following serological screening, immunity to HBV infection was found to be significantly (p<0.001) higher (56.7%) in the post-vaccination population than in the pre-vaccination population (15.5%). Within the post-vaccination population alone, immunity was found to wane with increasing age from 76.1 % in those 1-5 years of age to 50.0% in those 6-10 years and 44.2% in those 11-15 years of age. Chronic carriage on the other hand was significantly (p=0.008) reduced in the post-vaccination population with 1.5% HBsAg prevalence as compared to 4.0% in the pre-vaccination population. Within the different age strata, chronic carriage increased with increasing age (0.5% in 1-5 years; 1.3% in 6-10 years; 2.5% in 11-15 years). Overall, no acute HBV infection was detected within the post-vaccination population, while a 14.6% prevalence rate of acute HBV infection was found for the pre-vaccination population. From the subset analyses, immunity was found to be significantly (p<0.001) higher in the HIV uninfected population as compared to the HIV infected population; 82.5% versus 22.0% in the post-vaccination population and 26.7% versus 0% in the pre-vaccination population, while chronic carriage was found to be higher in the HIV infected population than in the HIV uninfected population. Following molecular characterization of the HBV S gene, it was revealed that the majority of the viral isolates were genotype A, with only 1 genotype D isolate found. A number of notable amino acid i$ variations were also detected within the antigenic region of the HBsAg of viral isolates, inCluding the K122R, N131T, T143S, and E164D mutations. Conclusion: Introduction of the hepatitis B vaccine into EPI-SA has shown remarkable success in children under the age of 5 years. Overall, immunity and chronic carriage of HBV within the post-vaccination population has been greatly impacted by hepatitis B immunization. Within the HIV infected population, susceptibility to HBV infection remains a cause for concern. Finally, although amino acid variations within the viral HBsAg are present, vaccine escape-related mutants appear to be rare or even absent within the South African population. vii

Sub-Saharan Africa has a high prevalence of hepatitis B virus (HBV) infections. Health care workers (HCWs) are at high risk of contracting HBV infection through their occupation. Vaccination of HCWs against HBV is standard practice in many countries, but is often not implemented in resource-poor settings. We aimed with this cross-sectional study to determine HBV prevalence, HCW vaccination status, and the risk factors for HCWs contracting HBV infection in Tanzania. We enrolled 600 HCWs from a tertiary Tanzanian hospital. Their demographics, medical histories, HBV vaccination details and risk factors for contracting blood-borne infections were collected using a standardized questionnaire. Serum samples were tested for HBV and hepatitis C virus (HCV) markers by ELISA techniques, PCR and an anti-HBs rapid test. HCWs were divided in two subgroups: those at risk of contracting HBV (rHCW 79.2 %) via exposure to potentially infectious materials, and those considered not at risk of contracting HBV (nrHCW, 20.8 %). The overall prevalence of chronic HBV infection (HBsAg+, anti-HBc+, anti-HBs-) was 7.0 % (42/598). Chronic HBV infection was found in 7.4 % of rHCW versus 5.6 % of nrHCW (p-value = 0.484). HCWs susceptible to HBV (HBsAg-, anti-HBc-, anti-HBs-) comprised 31.3 %. HBV immunity achieved either by healed HBV infection (HBsAg-, anti-HBc+, anti-HBs+) or by vaccination (HBsAg-, anti-HBc-, anti-HBs+) comprised 36.5 % and 20.2 %, respectively. 4.8 % of participants had indeterminate results (HBsAg-, anti-HBc+, anti-HBc-IgM-, anti-HBs-). Only 77.1 % of HCWs who received a full vaccination course had an anti-HBs titer >10 ml/U. An anti-HBs point-of-care test was 80.7 % sensitive and 96.9 % specific. There was a significantly higher risk for contracting HBV (anti-HBc+) among those HCW at occupational risk (rHCW) of older age (odds ratios (OR) in rHCW 3.297, p < 0.0001 vs. nrHCW 1.385, p = 0.606) and among those HCW being employed more than 11 years (OR 2.51, p < 0.0001***). HCV prevalence was low (HCV antibodies 1.2 % and HCV-RNA 0.3 %). Chronic HBV infection is common among Tanzanian HCWs. One third of HCWs were susceptible to HBV infection, highlighting the need for vaccination. Due to high prevalence of naturally acquired immunity against HBV pre-testing might be a useful tool to identify susceptible individuals. / Die Studie konnte in einem Krankenhaus der Maximalversorgung im Norden Tansanias eine hohe Prävalenz chronischer Hepatitis B-Infektionen beim Gesundheitspersonal zeigen. Weiterhin hatten die Teilnehmer ein hohes Risiko, eine HBV-Infektion im Laufe ihres Berufslebens zu erwerben. Bezüglich der Hepatitis C-Infektion zeigte sich insgesamt eine sehr niedrige Prävalenz. Ein besonders hohes Risiko, mit Hepatitis B infiziert zu werden, hatte Personal mit direktem Kontakt zu Blut oder Nadelmaterial. Ein Drittel des Krankenhauspersonals wies keine Immunität gegen Hepatitis B auf und war somit weiterhin einem Infektionsrisiko ausgesetzt. Etwas mehr als ein Drittel des Kollektivs wies die Antigen-/Antikörperkonstellation einer ausgeheilten Infektion auf. Der Infektionszeitpunkt ist aufgrund der häufig inapparenten klinischen Verläufe retrospektiv nicht zu eruieren. Ein weiterer Teil konnte mittels Immunisierung durch eine bereits im Vorfeld durch Hilfsgelder finanzierte Impfaktion eine Immunität erwerben. Der Impferfolg wurde nach dieser Impfaktion jedoch nicht serologisch verifiziert. Bei 40 Personen, die angaben an der Impfaktion teilgenommen zu haben, konnten keinerlei Antikörper nachgewiesen werden. Retrospektiv zeigte die Impfaktion mit 76% eine niedrige Erfolgsrate, was unter anderem auf einen hohen Teil an bereits HBV-Infizieren Teilnehmer zurückzuführen ist, bei denen eine Impfung nutzlos ist.

The human hepatitis B virus (HBV) is a small hepatotropic virus, which affects approximately 350 million chronic sufferers worldwide. It has a compact 3.2 kbp dsDNA genome encoding four major overlapping genes namely core, polymerase, surface and X required for its replication. The virus synthesises a pregenomic RNA (pgRNA) which functions both as an RNA intermediate for reverse transcription into the DNA genome and as the mRNA for the translation of the core (C) and polymerase (P) proteins. The core overlaps the polymerase gene and is translated at a 10 to 1 ratio. The polymerase gene translated from the P AUG codon is preceded by at least 4 upstream AUG codons (uAUGs), namely C AUG, C1 AUG, J AUG and C2 AUG. Various mechanisms have been implicated in the synthesis of the polymerase protein. This led to the currently accepted model which involves leaky scanning and a reinitiation mechanism in polymerase synthesis. However, multiple sequence alignment of the pgRNA revealed a short upstream open reading frame (uORF) highly conserved at the nucleotide level in all HBV subtypes and mammalian hepadnaviruses. This previously unreported uORF, designated as C0 ORF in this study is also conserved in its position and length. Past studies have either omitted this uORF in their test constructs or ignored its potential role. The C0 ORF has a conserved weak initiation context and is located within the epsilon structure within the 5' leader of the pgRNA, required for viral encapsidation. Importantly, the C0 ORF precedes and overlaps the core ORF, which may suggest an alternative model in which the core and polymerase may be translated and coordinately regulated. Fusion of the C0 ORF to luciferase showed for the first time that this uORF is translated through the detection of reporter activity (~20% of C) and also visualisation of the fusion protein via western analysis using anti-C0 and anti-luciferase antibodies. Subsequent removal of the C0 ORF implicated a role in repressing downstream core fusion protein synthesis in HepG2 cells. A similar repression was observed on J expression. To study the effect of C0 on downstream polymerase translation, a pgRNA-like DNA construct was made and subsequent mutations introduced. Mutation of the C0 AUG led to an increase in initiation at the downstream P AUG. Alteration of the existing weak initiation context to an optimal context which favours stronger initiation consistently showed a potential role for C0 ORF in facilitating reinitiation at certain downstream initiation codons including P AUG. Mutations of other uAUGs preceding the P AUG were also done to better understand their roles in regulating polymerase synthesis. The removal of the C AUG markedly increased expression from the P AUG. This study revealed other internal uAUGs in-frame to the C AUG, namely the C1 and C2 AUGs are also effectively translated, further reducing availability of translating ribosomes to downstream P AUG. Indeed the removal of the C1 and C2 AUGs led to a corresponding increase in initiation from the P AUG. Initiation at the internal J AUG was also reported and its removal showed a significant decrease in expression from the P AUG, consistent with the previous model implicating reinitiation at the P initiation site after translation of the short J ORF. The inhibitory role of the 5 uAUGs prior to the P AUG were confirmed when all were removed, giving rise to translation almost equal to that at C AUG. Taken together, these results suggest a new model in which the HBV C0 ORF plays a key role in controlling core and polymerase synthesis by repressing core translation and making available more ribosomes to downstream AUGs possibly facilitating translation reinitiation. In addition, the translation of the C0 ORF across the [epsilon] region may also preclude encapsidation, potentially acting as a switch discriminating the pgRNA template between encapsidation and translation. Therefore, the highly conserved [epsilon] region and C0 ORF present an excellent target for molecular based antiviral drugs (antisense oligonucleotides, aptamers, ribozymes) potentially providing new anti HBV drugs.

The human hepatitis B virus (HBV) is a small hepatotropic virus, which affects approximately 350 million chronic sufferers worldwide. It has a compact 3.2 kbp dsDNA genome encoding four major overlapping genes namely core, polymerase, surface and X required for its replication. The virus synthesises a pregenomic RNA (pgRNA) which functions both as an RNA intermediate for reverse transcription into the DNA genome and as the mRNA for the translation of the core (C) and polymerase (P) proteins. The core overlaps the polymerase gene and is translated at a 10 to 1 ratio. The polymerase gene translated from the P AUG codon is preceded by at least 4 upstream AUG codons (uAUGs), namely C AUG, C1 AUG, J AUG and C2 AUG. Various mechanisms have been implicated in the synthesis of the polymerase protein. This led to the currently accepted model which involves leaky scanning and a reinitiation mechanism in polymerase synthesis. However, multiple sequence alignment of the pgRNA revealed a short upstream open reading frame (uORF) highly conserved at the nucleotide level in all HBV subtypes and mammalian hepadnaviruses. This previously unreported uORF, designated as C0 ORF in this study is also conserved in its position and length. Past studies have either omitted this uORF in their test constructs or ignored its potential role. The C0 ORF has a conserved weak initiation context and is located within the epsilon structure within the 5� leader of the pgRNA, required for viral encapsidation. Importantly, the C0 ORF precedes and overlaps the core ORF, which may suggest an alternative model in which the core and polymerase may be translated and coordinately regulated. Fusion of the C0 ORF to luciferase showed for the first time that this uORF is translated through the detection of reporter activity (~20% of C) and also visualisation of the fusion protein via western analysis using anti-C0 and anti-luciferase antibodies. Subsequent removal of the C0 ORF implicated a role in repressing downstream core fusion protein synthesis in HepG2 cells. A similar repression was observed on J expression. To study the effect of C0 on downstream polymerase translation, a pgRNA-like DNA construct was made and subsequent mutations introduced. Mutation of the C0 AUG led to an increase in initiation at the downstream P AUG. Alteration of the existing weak initiation context to an optimal context which favours stronger initiation consistently showed a potential role for C0 ORF in facilitating reinitiation at certain downstream initiation codons including P AUG. Mutations of other uAUGs preceding the P AUG were also done to better understand their roles in regulating polymerase synthesis. The removal of the C AUG markedly increased expression from the P AUG. This study revealed other internal uAUGs in-frame to the C AUG, namely the C1 and C2 AUGs are also effectively translated, further reducing availability of translating ribosomes to downstream P AUG. Indeed the removal of the C1 and C2 AUGs led to a corresponding increase in initiation from the P AUG. Initiation at the internal J AUG was also reported and its removal showed a significant decrease in expression from the P AUG, consistent with the previous model implicating reinitiation at the P initiation site after translation of the short J ORF. The inhibitory role of the 5 uAUGs prior to the P AUG were confirmed when all were removed, giving rise to translation almost equal to that at C AUG. Taken together, these results suggest a new model in which the HBV C0 ORF plays a key role in controlling core and polymerase synthesis by repressing core translation and making available more ribosomes to downstream AUGs possibly facilitating translation reinitiation. In addition, the translation of the C0 ORF across the [epsilon] region may also preclude encapsidation, potentially acting as a switch discriminating the pgRNA template between encapsidation and translation. Therefore, the highly conserved [epsilon] region and C0 ORF present an excellent target for molecular based antiviral drugs (antisense oligonucleotides, aptamers, ribozymes) potentially providing new anti HBV drugs.

Thesis (M. Phil.)--University of Hong Kong, 2009. / Includes bibliographical references (leaves 77-109). Also available in print.

Thesis (M. Phil.)--University of Hong Kong, 2001. / Includes bibliographical references (leaves 93-119).