Thesis (MScMedSc))--Stellenbosch University, 2012. / Includes bibliography / ENGLISH ABSTRACT: Despite the availability of Hepatitis B virus (HBV) vaccination for over three decades, this infection remains a major public health problem. Whilst the WHO recommends giving a birth dose of the vaccine, in South Africa, routine infant HBV vaccination commences at six weeks of age. This schedule is based on data from the pre-HIV era which showed transmission occurred via the horizontal, rather than the vertical route. In the era of HIV however, maternal HIV co-infection may release HBV from immune control, resulting in higher HBV loads and increasing the risk of vertical transmission. The aim of this study was to determine the prevalence and character of HBV infection in HIV-exposed infected and uninfected infants. Residual plasma samples from routine HIV nucleic acid testing of 1000 HIV-exposed infants aged between 0 and 18 months from the Western Cape were tested. Samples were tested for HBsAg by ELISA (Murex HBsAg Version 3) and confirmed by neutralisation. HBV DNA was quantified using an in-house real-time PCR assay. Infants with HBsAg positive samples were followed up and a blood sample was collected from mother and child. Those HBsAg positive samples were tested for HBeAg/antiHBe (Diasorin) and HBsAg negative samples were tested for antiHBs. HBV DNA was quantified. The surface gene was sequenced and the HBV genotype determined by phylogenetic analysis using HepSEQ (www.hepseq.org.uk). Whole genome sequencing was also performed. Of 1000 samples tested, four samples were positive for HBsAg and/or HBV DNA, indicating a prevalence of HBV transmission of 0.4%. At follow-up, two of three infected infants were positive for HBsAg, with HBV viral loads of greater than 108 IU/ml. The third infant was found to have cleared his infection and the fourth child was lost to follow up. These infected infants had all received HBV vaccination. All four mothers were HBeAg positive. Sequencing analysis showed the HBV strains from the two infants and four mothers belonged to subgenotype A1. The two mother-child paired sequences were identical. The data from this study shows that vertical transmission of HBV infection in HIV-exposed infants from the Western Cape is occurring, despite vaccination. Data from the Western Cape, showing an HBV prevalence of 3.4% in HIV-infected pregnant women, and those presented here suggest a vertical transmission rate of HBV of 12%. This is despite the widespread use of tenofovir and lamivudine in HIV-infected women with low CD4 counts. This study provides data supporting calls to bring HBV vaccination closer to the time of birth. Further work is urgently needed to confirm these findings and to determine the rates of transmission in HIV-unexposed infants. / AFRIKAANSE OPSOMMING: Ten spyte van die beskikbaarheid van die Hepatitis B virus (HBV) inenting vir meer as drie dekades, hierdie infeksie bly 'n groot openbare gesondheid probleem. Terwyl die WGO aan beveel dat'n geboorte dosis van die entstof, in Suid-Afrika, roetine baba HBV inenting op die ouderdom van ses weke gegee word. Hierdie skedule is gebaseer op data van die pre-MIV era wat getoon het dat die oordrag plaasgevind het via die horisontale, eerder as die vertikale roete. In die era van MIV egter, moeder MIV ko-infeksie kan HBV vrylaat van immuun beheer, wat lei in hoër HBV vlakke en die verhoging van die risiko van vertikale oordrag. Die doel van hierdie studie was om die voorkoms en karakter van die HBV infeksie in MIV-besmette en onbesmette babas te bepaal. Residuele plasma monsters van roetine-MIV-nukleïensuur toetse van 'n 1000 MIV-blootgestelde babas tussen die ouderdomme van 0 en 18 maande van die Wes-Kaap was getoets. Monsters was getoets vir HBsAg deur ELISA (Murex HBsAg Version 3) en bevestig deur neutralisering. HBV DNA is gekwantifiseer deur gebruik te maak van 'n in-huis real-time PCR assay. Babas met HBsAg positiewe monsters was opgevolg en 'n bloedmonster is versamel van moeder en kind. Die HBsAg positiewe monsters was getoets vir HBeAg/antiHBe (Diasorin) en HBsAg negatiewe monsters was getoets vir antiHBs. HBV DNA was gekwantifiseer. Die oppervlak gene volgorde en genotipes was bepaal deur filogenetiese analise met behulp van HepSEQ (www.hepseq.org.uk). Die hele genoom-volgordebepaling was ook uitgevoer. Van die 1000 monsters wat getoets was, was vier monsters positief vir HBsAg en of HBV DNA, dit dui op 'n voorkoms van HBV oordrag van 0.4%. By op volg, twee van die drie besmette babas was positief vir HBsAg, met HBV virale vlakke van groter as 108 IE/ml. Die derde baba was gevind dat sy infeksie opgeklaar het en die vierde kind was verlore as gevolg van op volg. Hierdie besmette babas het almal HBV inenting ontvang. Al vier moeders was HBeAg positief. Volgordebepaling analise het getoon die HBV stamme van die twee babas en vier moeders behoort aan subgenotype A1. Die twee moeder-kind gepaarde rye was homoloë. Die data van hierdie studie toon dat die vertikale oordrag van HBV infeksie in MIV-blootgestelde babas van die Wes-Kaap vind plaas, ten spyte van inenting. Data van die Wes-Kaap, wat 'n HBV voorkoms van 3.4% in MIV-besmette swanger vroue, en dié wat hier aangebied is dui op 'n vertikale oordrag koers van 12% van die HBV. Dit is ten spyte van die wydverspreide gebruik van tenofovir en lamivudine in MIV-geïnfekteerde vroue met 'n lae CD4-telling. Hierdie studie bied data wat ondersteunende oproepe van HBV inenting nader aan die tyd van die geboorte bring. Verdere werk is dringend nodig om die bevindinge te bevestig en die pryse van die oordrag in MIV-blootgestelde babas te bepaal. / National Health Laboratory Service Research Trust / Poliomyelitis Research Foundation (PRF) / Harry Crossley Foundation / Stellenbosch University