Abstract

The clinical course of infections with the hepatitis B virus (HBV) substantially varies between individuals, as a consequence of a complex interplay between viral, hosts, environmental, and other factors.

Due to the high genetic variability of HBV, the virus can be categorized into different HBV genotypes, which considerably differ with respect to geographical distribution, transmission routes, disease progression, responses to antiviral therapy or vaccination, and clinical outcome measures such as cirrhosis or hepatocellular carcinoma.

In this study, genotype-specific primers were used to genotype HBV and relate these genotypes to disease severity based on ALT and AST levels.

The influence of alcohol consumption on disease severity and on viral strains was also investigated. A total of 30 samples positive for HBsAg from infected individuals with mean age 29.4±7.2 years were subjected to PCR for the amplification of the S gene and only 11 samples were successfully amplified.

Among the 11 amplicons, 7 were genotype C and 4 others had mixed genotypes D/E/F. The majority of the patients were from areas within the southwest region.

There was no evidence of significance in the mean AST and ALT levels in patients infected with genotype C and mix genotypes D/E/F (p>0.05).

Again, There was no evidence of a significant difference in the distribution of genotypes based on alcohol intake (p>0.05).

There was no evidence of significance in the mean AST and ALT levels in patients who were alcoholics and in patients who didn’t consume alcohol (p>0.05).

However, there was evidence of significance in the mean ALT levels of acute, chronic, and alcoholic male and female patients and there was also evidence of significance in the distribution of genotypes based on age groups (p<0.05). There was no evidence of a significant difference in the distribution of genotypes based on alcohol intake (p>0.05).

CHAPTER ONE

INTRODUCTION AND LITERATURE REVIEW

1.1       Introduction

Hepatitis B is a potentially life-threatening liver infection caused by the hepatitis B virus (HBV) and it is a major public health concern (WHO, 2015).

It is the 10th leading cause of death worldwide, with a significant number of chronic carriers progressing to liver cirrhosis or hepatocellular carcinoma (HCC), both conditions thought to kill over a million individuals annually (Wright et al., 2006).

About 240 million people are chronically infected with hepatitis B, with approximately 780 000 persons dying each year from hepatitis B infection, 650 000 from cirrhosis and liver cancer due to chronic hepatitis B infection, and another 130 000 from acute hepatitis B (WHO, 2015).

Hepatitis B virus belongs to the genus Orthohepadnavirus of the hepadnaviridae family. It is composed of circular double-stranded DNA particles where the negative strand is complete and the positive one is incomplete at the 5’ end.

It is an enveloped virus, 42nm in diameter, and with 3200 nucleotides (Okamoto et a., 1988). It can be classified phenotypically into four subtypes, which in turn may be further classified according to antigenic determinants of the surface antigen (HBsAg): adw, ayw, adr, ady (Okamoto H et al., 1988).

HBV can also be classified by genotype into eight strains, ranging from A to H (Kidd-Ljunggren et al., 2002). Their structural and functional differences are associated with clinical severity, treatment failure, and possible interference with vaccine response (Noeder et al., 2004). These genotypes can vary up to 8% within its genome (Noeder et al., 2004).

The Different genotypes have a varied distribution; genotype A has a universal distribution, being the predominant genotype in Europe, North America, Africa, and India. Genotype B and C are predominant in Eastern and South East Asia and Australia. Genotype D is mainly found in the Middle East and the Mediterranean.

Genotype E seems to be predominant in West Africa, whereas genotype G is distributed throughout the United States, Mexico, and France. Genotype F is mainly found in central and south America and Alaska. Finally, genotype Is unique to Central America and United States (Noeder et al., 2004, Campos et al., 2005, Weber et al., 2006).

1.2. Literature Review

1.2.1 Background

Hepatitis B virus genotypes have the potential to infect individuals leading to chronic infections with various stages of progressive liver disease including cirrhosis and hepatocellular carcinoma as well as death. Disease severity has been found to be influenced by viral genotype, host, and environmental factors. In general, HBV genotypes C and D are associated with more severe liver disease than B and A respectively.

However, there are various studies that suggest patients infected with HBV genotype B have more severe liver disease including cirrhosis and HCC than patients infected with genotype C (Yuen et al., 2003, Ding et al., 2002, Kobayashi et al., 2002).

Individuals infected with HBV genotypes A or C have been observed to be more likely to progress to chronic hepatitis than patients exposed to genotypes D and B, however, all genotypes can lead to acute or chronic infections (Kao et al., 2002, Mayerat et al., 1999).

Patients infected with HBV genotype A have been observed to have a higher rate of clearance for HBsAg and HBV DNA as well as biochemical remission than either genotype D or F (Sanchez et al., 2002).

Biopsies from patients infected with genotype C reveal more advanced fibrotic liver disease and a higher incidence of cirrhosis compared to genotype B, indicating that HBV genotype B may require a longer period of time for progression to fibrosis than genotype C (Sumi et al., 2003).

Death related to liver disease seems to be more frequent for patients infected with HBV genotype F than in genotype A or D, however, this observation was derived from a study with a limited number of patients(n=19) (Sanchez et al., 2002). Studies revealed that diversity within the HBV genome is directly associated with cirrhosis as well as HCC incidence and outcome, (Ding et al., 2002).

In order to accurately investigate the impact of different genotypes of HBV on different aspects of infection from prophylaxis, diagnosis, and therapy, it is crucial to agree to a holistic classification.

Numerous HBV strains have been described through PCR and sequencing, however, many disregarded well-established HBV Genotype definitions, which has resulted in several misclassifications. Subsequently, experts in the field agreed that the classification of HBV should be mended and rectified (Chin et al., 2003).

There are several reviews or commentary articles regarding the misclassification of HBV that describes the history of the identification of different genotypes. However, the reclassification and renovation of this system have been considered less often.

It is believed that recombination is the main cause of misclassifications and major evolutionary characteristics of HBV should be investigated to help identify strains that require additional analysis for proper classification (Kurbanov et al., 2008).

Besides this factor, massive but gradual conversion of the geographical distribution of HBV should be concomitantly investigated. However, antiviral drugs are available for HBV-infected individuals that may prevent the critical consequences of chronic liver disease, which emphasizes the need for identifying infected individuals and monitoring the prevalence of the disease (Weinbaum et al., 2009).

The prevalence of HBV and its modes of transmission vary geographically, and it can be classified into three endemic patterns (Knipe et al., 2013, Kowdley et al., 2004).

Around 45% of the world’s populations live in regions of high endemicity such as Southeast Asia and Sub-Saharan Africa (Essam et al., 2014) where transmission occurs mainly vertically by a perinatal passage from HBV-infected mothers to their newborns (Zuckerman et al., 2005).

However, certain types of behaviors increase the risk for contracting HBV such as the use of contaminated needles during acupuncture, intravenous drug abuse, ear piercing and tattooing, sexually active heterosexuals or homosexuals with more than one sexual partner, health care workers, hemodialysis, and blood transfusion (WHO, 2015).

Unfortunately, treatment against this virus is not always accessible for most people in developing countries (Fouelifack et al., 2012). It is, therefore, necessary to genotype the various strains of the virus in order to monitor disease progression and effect necessary intervention measures to reduce progressive liver damage.

1.2.2.   Hepatitis B Virus

1.2.3 HBV genotypes and response to anti-viral therapy

1.2.4 The liver, serum alanine aminotransferase (ALT), aspartate aminotransferase (AST) concentrations, and De Ritis ratio.

1.2.5 Interplay between alcohol and HBV in liver disease progression

1.2.6 Surveillance and control (WHO, 2016)

1.2.7 Prevention and treatment (WHO, 2016)

 

1.3. Rationale

The clinical course of infections with HBV substantially varies between individuals, as a consequence of the complex interplay between viral, host, environmental, and other factors.

The HBV demonstrates high genetic variability and can therefore be categorized into different HBV genotypes which considerably differ with respect to geographical distribution, transmission routes, disease progression, responses to antiviral therapy or vaccination, and clinical outcome measures such as cirrhosis or hepatocellular carcinoma.

This study was carried out to investigate the possible relationship between HBV genotypes and liver disease progression.

 

1.4. Hypothesis

Hepatitis B virus from infected individuals attending the Regional Hospital Buea demonstrates a high degree of genetic diversity.

 

1.5. Study Objectives

1.5.1. Overall Objective

The main aim of this study was to investigate the genetic diversity of the hepatitis B virus from infected individuals attending the Regional Hospital Buea.

1.5.2. Specific Objectives

1. To identify the different genotypes of the HBV amongst infected individuals using type-specific primers.
2. To investigate the existence of a possible relationship between virus genotypes and disease progression.
3. To investigate the socio-demographic risk factors associated with liver injury.