Hepatitis B virus (HBV) is a double-stranded, enveloped virus of the Hepadnaviridae family. The Hepadna virus family has the smallest genome of all replication competent animal DNA viruses. The single most important member of the family is HBV.
The hepatitis B virion consists of a surface and a core, which contains a DNA polymerase and the e antigen. The DNA structure is double-stranded and circular with four major genes: the S (surface), the C (core), the P (polymerase), and the X (transcriptional transactivating). The S gene consists of three regions—S, pre-S1, and pre-S2—that encode the envelope protein (HBsAg). HBsAg is a lipoprotein of the viral envelope that circulates in the blood as spherical and tubular particles. The C gene is divided into two regions, the pre-core and the core, and codes for two different proteins, the core antigen (HBcAg) and the e antigen (HBeAg).
HBV strains are classified into eight genotypes designated A to H, most of which have a characteristic geographical distribution (Cao 2009; Tanwar and Dusheiko 2012). More recently, two additional genotypes, I and J, have been described in Asia (Tatematsu et al. 2009; Tran et al. 2008). Except for these newly identified genotypes, the geographic distributions of HBV genotypes are well characterized. Genotype A is highly prevalent in sub-Saharan Africa, Northern Europe, and Western Africa. Genotypes B and C are the major variants in South and South East Asia and the Pacific region. Genotype D is prevalent in Africa, Europe, the Mediterranean region and India. Genotype E is restricted to West Africa. Genotype F is found in Central and South America. Genotype G has been reported in France, Germany, and the United States and genotype H is found in Central America (Kurbanov et al. 2010; Lin and Kao 2011).
The genotypes A, B, C, D, and F have further been subdivided in up to four major subgenotypes and several minor genotypes, now identified by Arabic numerals.
The HBV infection is controlled by cellular and humoral immune responses. It can be tracked through serological detection of the virus particles or the antibodies raised by the immune system to target the virus. The presence of hepatitis B surface and/or hepatitis B core antibodies (anti-HBs and anti-HBc) in the absence of HBsAg is generally taken to indicate resolution of infection and provides evidence of previous HBV infection. Persistence of HBV infection (chronic carrier) is diagnosed by the detection of HBsAg in the blood for at least 6 months or through detection of HBV-DNA even in the absence of detectable HBsAg in patients with occult HBV infection. HBeAg is an alternatively processed protein of the pre-core gene that is only synthesized under conditions of high viral replication. HBV-DNA is used as an indicator for viral replication expressed as IU/mL or copies/mL (the value of copies/mL is approximately 5 times more than the IU units). There is a clear association between serum HBV-DNA levels (viral load) and prognosis: the cumulative incidence of cirrhosis or hepatocellular carcinoma (HCC) being 4.5 and 1.3 per cent, respectively, in persons with DNA levels less than 300 copies/mL (corresponding to 50 IU/mL), while it is 36.2 and 14.9 per cent, respectively, in persons with DNA levels of more than or equal to 106 copies/mL (corresponding to 2 × 105 IU/mL). This is the rationale for treating patients with high levels of HBV DNA (Chen et al. 2006; Lok and McMahon 2007).
Globally, hepatitis B is one of the most common infectious diseases. Estimates indicate that about 2 billion people (i.e. about 30 per cent of the world population) have been infected with HBV worldwide, with over 240 million people being chronic carriers (World Health Organization (WHO) 2012). On the basis of sero-epidemiological surveys, the WHO has classified countries into three levels of endemicity according to the prevalence of chronic HBsAg carriage (Fig. 8.16.1): high (8 per cent or greater), intermediate (2–7 per cent), and low (less than 2 per cent) (WHO 2004).
HBV is transmitted by either percutaneous or mucous membrane contact with infected blood or other body fluid. The virus is found in highest concentrations in blood and serous exudates (up to 109 virions/mL). The primary routes of transmission are perinatal, early childhood exposure (often called horizontal transmission), sexual contact, and percutaneous exposure to blood or infectious body fluids (i.e. injections, needle stick, blood transfusion, tattoos).
Most perinatal infections occur among infants of pregnant women with chronic HBV infection. The likelihood of an infant developing chronic HBV infection is 70–90 per cent for those born to HBeAg-positive mothers (corresponding to high titres of HBV DNA) and less than 15 per cent for those born to HBeAg-negative mothers. Most early childhood infections occur in households of persons with chronic HBV infection. The most probable mechanism involves unapparent percutaneous or permucosal contact with infectious body fluids (e.g. bites, breaks in the skin, dermatological lesions, skin ulcers). Sexual transmission has been estimated to account for 50 per cent of new infections among adults in industrialized countries. The most common risk factors include multiple sex partners and history of a sexually transmitted infection. Finally, unsafe injections and other unsafe percutaneous or permucosal procedures (such as cocaine snorting) are a major source of blood-borne pathogen transmission (HBV, hepatitis C virus (HCV), human immunodeficiency virus (HIV)) in many countries. The risk of HBV infection from needle stick exposure to HBsAg-positive blood is approximately 30 per cent and worldwide unsafe injection practices account for approximately 8–16 million HBV infections each year.
In areas of high endemicity, the lifetime risk of HBV infection is more than 60 per cent, and most infections occur during the perinatal period (transmission from mother to child) or during early childhood. In areas of intermediate endemicity, the lifetime risk of HBV infection varies between 20 and 60 per cent, and infections occur in all age groups through the four modes of transmission, but primarily in infants and children. In areas of low endemicity, infection occurs primarily in adult life by sexual or parenteral transmission (e.g. through drug use). Although acute infection is more often clinically expressed in adults, infections in infants and pre-school age children are at greatest risk of becoming chronic, thereby increasing the risk of cirrhosis and primary HCC later in life. The precise mechanism by which carrier rates are influenced by age of infection is unknown but probably relates to the effect of age on the immune system’s ability to clear and eliminate the infection.
Approximately 75 per cent of the world’s chronic hepatitis B carriers live in Asian countries. China ranks highest, with 100 million hepatitis B carriers, and India the second highest, with a carrier pool of 35 million (Tandon and Tandon 1997). Importantly, chronic carriers of HBV are not only at risk of developing long-term progression of the infection but also represent a significant source and reservoir of infection to others.
A model developed in 2005 estimated that in the year 2000, 620,000 persons died worldwide from HBV-related causes: 580,000 (94 per cent) from chronic infection-related cirrhosis and HCC and 40,000 (6 per cent) from acute HBV infection. Infections acquired during the perinatal period, in early childhood (<5 years old), and at 5 years of age and older accounted for 21 per cent, 48 per cent, and 31 per cent of deaths, respectively (Goldstein et al. 2005).
Besides the age at which the infection is acquired, some of the variation in outcome of HBV infection may be related to the genetic heterogeneity of the virus. Progression to chronic infection appears to occur more frequently following acute infection with genotypes A and D than with the other genotypes (Tanwar and Dusheiko 2012). Chronic infection with genotype A and B appears to have a better prognosis than genotype C and D. Pre-core mutant infection is also most common in genotypes B, C, and D, which explains why pre-core mutant infection is more common in Asia and Southern Europe.
Acute hepatitis B has a long incubation period ranging from 15 to 180 days (90 days on average) during which the individual is infectious. Individual responses to the infection vary greatly. One-third of the individuals have subclinical infection; one-third experience a mild ‘flu-like’ illness without jaundice; and the remaining one-third develop jaundice with dark urine, extreme fatigue, anorexia, and abdominal pain. Jaundice usually peaks within 1–2 weeks and then gradually subsides. About 95 per cent of adults recover completely, although this may require 6 months or more with persistent tiredness. A small proportion (1 per cent) of adults develop fulminant hepatitis, an exceptionally severe form of the disease which can be fatal requiring in two-thirds of cases an emergency liver transplant (Sherlock 1993). About 5–10 per cent of acutely infected adults and 50–90 per cent of newborns will become chronically infected and remain infectious.
The natural history of chronic HBV infection can vary dramatically between individuals. Risk factors which affect progression to chronic hepatitis, cirrhosis, and HCC include male gender, viral load, elevated alanine aminotransferase (ALT), genotype, and degree of fibrosis on liver biopsy. Some patients with persistent HBV infection will develop the condition commonly referred to as a chronic carrier state (HBsAg positivity in two occasions 6 months apart). These patients, who are still potentially infectious, have no symptoms and no abnormalities on laboratory testing. Some individuals with chronic HBV infection will have clinically insignificant or minimal liver disease and never develop complications. Others will have clinically apparent chronic hepatitis. Chronic infection with HBV can be either ‘replicative’ or ‘non-replicative’. The ‘replicative’ phase or immune tolerance phase, characterized by positive HBeAg and high viral load (> 2 IU/mL, in particular if > 20 IU/mL), is often present in newborns and children of HBsAg-positive mothers. In ‘non-replicative’ infection, the rate of viral replication in the liver is low, serum HBV DNA concentration is generally low, and HBeAg is not detected. In these inactive HBsAg carriers, reactivation can occur either spontaneously or by immune suppression. Patients with chronic HBV and replicative infection generally have a worse prognosis and a greater chance of developing cirrhosis and/or HCC (Chen et al. 2006). In rare strains of HBV with mutations in the pre-core gene, replicative infection can occur in the absence of detectable serum HBeAg.
HBV treatment depends on the phase of chronic HBV infection. Viral replication is necessary to cause liver injury, but the host immune system activation plays the main role in causing hepatocellular damage. As HBV is not directly cytopathic, if the patient is immunotolerant, he may present high viral load without necro-inflammation. When immunotolerance is lost, the host immune system causes liver injury. This is the immune clearance phase, when ALT increases and necro-inflammation and, consequently, liver fibrosis is found in the liver. A long-term immune clearance phase causes more fibrosis and compromises liver function. If the host immune system imposes immune control against the virus, viral replication dramatically drops down and liver damage almost disappears, but the HBV cannot be eliminated because its DNA is already integrated in the host cells. This is the inactive phase, which can reverse to the immunoclearance phase in case of host immune depression or viral mutations. In this case, the necro-inflammatory activity returns.
Treatment is indicated if ALT is elevated, HBV-DNA is more than 2 IU/mL (European Association for the Study of the Liver 2012) or 20 IU/mL (Lok and McMahon 2009) and if there are signs of moderate or severe liver fibrosis.
The main goal of therapy for chronic HBV infection is to significantly suppress replication of HBV, thus preventing liver disease progression to cirrhosis and its complications, and reducing secondary spread. Treatment of chronic HBV infections has some limited success. Antiviral therapy will only rarely lead to complete resolution of persistent HBV infection (negativation of HBsAg). Furthermore, residual HBV DNA in the form of intra-nuclear covalently closed circular (ccc)-DNA may still be present in patients who lost HBsAg and seroconverted to anti-HBs, a situation which leads to occult HBV infection.
In patients who are HBeAg-positive, the goal of treatment is HBeAg seroconversion with sustained suppression of HBV DNA and rarely HBsAg loss or seroconversion. In those who are HBeAg-negative, the goal of treatment is sustained suppression of HBV DNA and, consequently, reduced liver injury as measured by ALT levels as well as HBsAg loss or seroconversion (which is achieved only on rare occasions).
Recommendation for therapy is dictated by the level of HBV DNA, liver enzymes and necro-inflammatory activity in liver biopsy. More recently, non-invasive methods to define the fibrosis stage are also accepted to indicate treatment, mainly in HBeAg negative patients (European Association for the Study of the Liver 2012).
Several therapies are now licensed: nucleo(t)side analogues and interferon-based therapy. The latter is more indicated in HBeAg positive patients, but in Europe it can also be indicated in selected cases of HBeAg negative HBV carriers. Depending on the defined outcome, approximately one-third of HBeAg patients respond to a 1-year course of α-interferon therapy, taking HBeAg/Anti-HBe seroconversion as the aim of the treatment.
Currently, interferon-based therapy appears to be superior to nucleo(t)side analogues, due to the relatively higher rate of anti-HBe seroconversion, the limited duration of treatment as compared to nucleos(t)ide analogues, the potential, albeit rare, HBsAg loss after 1 year of therapy, the lower overall cost and the absence of resistance (Hoofnagle et al. 2007). On the other hand, interferon causes more adverse events and must be administered subcutaneously. Because of that, many physicians and even patients do not choose interferon as the first-line treatment.
Treatment with nucleos(t)ide analogues is very effective in suppressing viral load but the end point of treatment is undetermined and long-term treatment is required, which remains costly and unavailable to the majority of those affected. Combination therapy (interferon-based and nucleo(t)side) does not lead to a better viral response.
There are nowadays many licensed nucleo(t)side analogues: lamivudine, telbivudine, entecavir, tenofovir, and tenofovir/entricitabine. Among these, entecavir and tenofovir are usually preferred, because of the higher genetic barrier (low probability of resistance) and higher potency.
The nucleo(t)side analogue based treatment has no time definition. In the vast majority of cases, the patient needs to be treated for a long time, but they are usually safe, without significant adverse effects.
Public health impact
HBV infection is a serious global health problem. Of the approximately 2 billion people who have been infected worldwide up to 2012, more than 240 million are chronic carriers of HBV (WHO 2012). Approximately 15–40 per cent of infected patients will develop cirrhosis, liver failure or HCC. HBV infection accounts for an estimated 600,000 deaths each year, mainly due to the consequences of chronic hepatitis, such as cirrhosis and liver cancer (Goldstein et al. 2005; Lavanchy 2004; Perz et al. 2006a). Because these complications mainly occur in adults who quite often were infected with HBV as children, most of the benefits of vaccination initiated 20 years ago have yet to be realized. Table 8.16.1 summarizes the global prevalence and mortality of HBV versus the observed prevalence and mortality of HCV and human immunodeficiency virus/acquired immune deficiency syndrome (HIV/AIDS). Another consequence, often underestimated, is the stigma that HBV carries to the individual, in the family setting, as well as in social and professional life.
Table 8.16.1 Global disease burden for hepatitis B, hepatitis C, and HIV/AIDS
Number of deaths per year
Source: data from World Health Organization, Global Health Observatory (WHO database HIV/Aids), Global epidemic and health care response (PowerPoint slides), Copyright © WHO 2011, available from http://www.who.int/hiv/data/en and World Health Organization, Prevention and Control of Viral Hepatitis Infection: Framework for Global Action, Copyright © WHO 2012, available from http://who.int/csr/disease/hepatitis/GHP_Framework_En.pdf?ua=1.
All major health authorities agree that the most effective approach to reducing the burden of HBV is primary prevention through universal vaccination and control of disease transmission. Interrupting the chain of infection requires knowledge of the mode of disease transmission and modification of behaviour through individual education to practice safe sex and good personal hygiene. Screening of all donated blood and maintenance of strict aseptic techniques with invasive health treatments have reduced the likelihood of contracting HBV.
Safe and effective HBV vaccines have been available since the 1980s, and immunization with HBV vaccine remains the most effective means of preventing HBV disease and its consequences worldwide. Although the vaccine will not cure chronic hepatitis, it is 95 per cent effective in preventing chronic infections from developing, and is the first vaccine against a major human cancer.
After the development of plasma-derived vaccines (in 1982), which continue to be used mostly in the low- and middle-income countries, recombinant DNA technology has allowed the expression of HBsAg in other organisms. As a result, different manufacturers have successfully developed recombinant DNA vaccines against HBV (commercialized in 1986).
Moreover, apart from monovalent vaccines against hepatitis B, a broad range of combination vaccines that include an HBV component exist, especially for vaccination during infancy and early childhood. Most of these simultaneously immunize against tetanus, diphtheria, and pertussis (with either a whole-cell or an acellular component); they may also include antigens for vaccination against polio and/or Haemophilus influenzae b. For each of these combination vaccines, it has been shown that the respective components remain sufficiently immunogenic, and that the combination vaccine is safe.
More recently, the so-called third-generation hepatitis B vaccines—based on the S-, pre-S1-, and pre-S2-antigens, or using new adjuvants—have been and are being developed. These vaccines specifically aim to enhance the immune response in immunocompromised persons and non-responders (Rendi-Wagner et al. 2006; Shouval et al. 1994).
Immunization against hepatitis B requires the intramuscular administration of three doses of vaccine given at 0, 1, and 6 months. More rapid protection (i.e. for healthcare workers exposed to HBV or the susceptible sexual partner of a patient with acute hepatitis B) can be achieved through the adoption of an alternative schedule using three doses of vaccine administered at 0, 1, and 2 months followed by a booster dose given at 12 months. The extensive use of both plasma-derived and recombinant HBV vaccines since their becoming available has confirmed their safety and excellent tolerability. However, in recent years, the safety of hepatitis B vaccine has been questioned, particularly in some countries. In 1998, several case reports from France raised concern that hepatitis B vaccination may lead to new cases or relapse of multiple sclerosis (MS) or other demyelinating diseases, including Guillain–Barré syndrome; however, no causal relation has been established (Duclos 2003). Hepatitis B vaccination is not contraindicated in pregnant or lactating women.
Seroprotection against HBV infection is defined as having an anti-HBs level 10 IU/L after complete immunization (Centers for Disease Control and Prevention 1987). Reviews on the use of HBV vaccine in neonates and infants report seroprotective levels of anti-HBs antibodies at 1 month after the last vaccine dose for all schedules in 98–100 per cent of vaccinees (Venters et al. 2004). While HBV vaccines generally induce an adequate immune response in over 95 per cent of fully vaccinated healthy persons, a huge interpersonal variability has been demonstrated in the immune response. The antibody response to hepatitis B vaccine has been shown to depend on the type, dosage and schedule of vaccination used, as well as on the age, the gender, genetic factors, co-morbidity, and the status of the immune system of the vaccinee (Hadler and Margolis 1992; Hollinger 1989). Immunodeficient patients, such as those undergoing haemodialysis or immunosuppressant therapy, require higher doses of vaccine and more injections (at months 0, 1, 2 and 6) to achieve an adequate and sustained immune response.
Follow-up studies have shown that vaccine-induced antibodies persist over periods of at least 20 years and that duration of anti-HBs positivity is related to the antibody peak level achieved after primary vaccination (Jilg et al. 1988; Leuridan and Van Damme 2011). Follow-up of successfully vaccinated people has shown that the antibody concentrations usually decline over time, but clinically significant breakthrough infections are rare. Those who have lost antibody over time after a successful vaccination usually show a rapid anamnestic response when boosted with an additional dose of vaccine given several years after the primary course of vaccination or when exposed to the HBV. This means that the immunological memory for HBsAg can outlast the anti-HBs antibody detection, providing long-term protection against acute disease and the development of the HBsAg carrier state (Banatvala and Van Damme 2003). Hence, for immunocompetent children and adults the routine administration of booster doses of vaccine does not appear necessary to sustain long-term protection (European Consensus Group 2000). Such conclusions are based on data collected during the first 10–20 years of vaccination in countries of both high and low endemicity (Kao and Chen 2005; Zanetti et al. 2005).
Since the availability of hepatitis B vaccines in industrialized countries, strategies for HBV control have stressed immunization of high-risk groups (e.g. homosexual men, healthcare workers, patients in sexually transmitted infection clinics, sex workers, drug users, people with multiple sex partners, household contacts of chronically infected persons) and the screening of pregnant women. As observed and reported in many countries, and though it is certainly desirable to immunize these persons, it is unlikely that such a programme limited to high-risk groups will control HBV infection in the community.
In 1991, the WHO called for all children to receive the HBV vaccine. Substantial progress has been made in implementing this WHO recommendation: by the end of 2012, 179 countries had implemented or were planning to implement a universal HBV immunization programme for newborns, infants, and/or adolescents. Of these, 147 (82 per cent) countries reported HBV infant vaccination coverage over 80 per cent after the third dose; these countries are mainly situated in Europe, North and South America, Northern Africa, and Australia (UNICEF and WHO 2012).
High coverage with the primary vaccine series among infants has the greatest overall impact on the prevalence of chronic HBV infection in children (WHO 2004). According to model-based predictions, universal HBV infant immunization (without administration of a birth dose of vaccine to prevent perinatal HBV infection), would prevent up to 75 per cent of global deaths from HBV-related causes, depending on the vaccination coverage for the complete series. Adding the birth dose would increase the proportion of deaths prevented up to 84 per cent (Goldstein et al. 2005).
In countries with high or intermediate disease endemicity, the most effective strategy is to incorporate the vaccine into the routine infant immunization schedule or to start immunization at birth (< 24 hours). Countries with lower prevalence may consider immunization of children or adolescents as an addition or an alternative to infant immunization (WHO 2004, 2006).
Indeed, the effectiveness of hepatitis B newborn and infant immunization programmes has already been demonstrated in a variety of countries and settings (André and Zuckerman 1994; Lee 1997; WHO 2001). The results of effective implementation of universal hepatitis B programmes have become apparent in terms of reduction not only in the incidence of acute hepatitis B infections, but also in the carrier rate in immunized cohorts and in hepatitis-B-related mortality—two ways to measure the impact of a hepatitis B vaccination programme (Coursaget et al. 1994).
In Taiwan, the HBsAg prevalence in children under 15 years of age decreased from 9.8 per cent in 1984 to 0.7 per cent in 1999 (Chan et al. 2004). In the Gambia, childhood HBsAg prevalence decreased from 10 per cent to 0.6 per cent since the introduction of the universal infant immunization programme (Viviani et al. 1999). Data in Hawaii show a 97 per cent reduction in the prevalence of HBsAg since the start of the infant hepatitis B vaccination programme in 1991. The incidence of new acute hepatitis B infections in children and adults was reduced from 4.5/100,000 in 1990 to 0 in the period 2002–2004 (Perz et al. 2006b). In Bristol Bay, Alaska, 3.2 per cent of children were HBsAg positive before universal hepatitis B immunization; 10 years later, no child under 10 years of age was HBsAg positive (Wainwright et al. 1997). Finally, surveillance data from Italy, where a universal programme was started in 1991 in infants as well as in adolescents, have shown a clear overall decline in the incidence of acute hepatitis B cases from 11/100,000 in 1987 to 3/100,000 in 2000 (Romano et al. 2004).
Hepatitis D virus
Hepatitis D virus (HDV) is a transmissible pathogen that requires the help of a hepadnavirus like HBV for its own replication—similar to viroids or plant virus satellite RNAs. Thus, in a natural setting, HDV is only found in patients who are also infected with HBV since the HDV RNA genomes are assembled using the envelope proteins of HBV and HDV buds through the HBsAg excretory pathway.
The HDV genome is a small single-stranded RNA genome composed of approximately 1680 bases with a unique circular conformation that is replicated using a host RNA polymerase. A rolling-circle model has been developed for its RNA replication, which is unique, at least among agents that infect animals. The HDV genome contains an open reading frame translated to the small (S-HD) and large (L-HD) proteins. The L-HD amino acid sequence is identical to S-HD with the addition of a carboxy-terminal extension of 19–20 amino acids following the editing of the S-HD stop codon during the viral RNA replication cycle. The S-HD is required for viral replication and might promote RNA polymerase II elongation of nascent HDV RNA, while L-HD is essential for HDV particle assembly (Tseng and Lai 2009).
There are two types of HDV infection: co-infection and super-infection (Rizzetto and Verme 1985). HDV and HBV can infect individuals simultaneously, transmitted by the same inoculums, characterizing a co-infection. On the other hand, the HDV can infect a chronic HBV carrier, characterizing a super-infection. A co-infection usually evolves into complete recovery, but the risk for severe acute hepatitis, even fulminant hepatitis, is higher than in the case of acute HBV mono-infection. A super-infection evolves toward chronicity in about 90 per cent of cases. Chronicity is associated with an increased risk of developing advanced chronic liver disease, early cirrhosis development, and hepatocarcinoma (Farci 2003; Smedile and Bugianesi 2005).
Eight HDV genotypes have been characterized to date on the basis of a small number of complete genome sequences with 19–38 per cent divergence at the nucleotide level of complete genomes (Hughes et al. 2011). The most frequent genotypes are: genotype I (includes the European, North American, African, and some Asian HDV isolates), genotype II (found in Japan, Taiwan, and Eastern Europe), genotype III (found exclusively in South America), genotype IV (found mainly in West-Africa) and genotype V (found in Central Africa).
The global distribution of the different genotypes of HBV and HDV is rather well known, although less is known on the types circulating among populations in remote areas and on the way the different viruses and their respective genotypes interact in multiple infected individuals. Little is also known on the viral transmission mechanisms driving the circulation of the endemic strains and epidemic outbreaks.
The prevalence of HDV infection increases in the equatorial subtropical and tropical zones, concentrating in certain population groups which are considered high endemicity models (Torres 1996). Preliminary data suggest that hepatitis delta in Brazil, endemic in the Western Amazon states, is more severe compared to other regions; however this needs further evidence (Paraná et al. 2008; Viana et al. 2005). In Western Europe, HDV is becoming rare, affecting around 5 per cent of chronic carriers (Rizzetto and Ciancio 2012).
In endemic areas, all HBV carriers should be further screened for delta hepatitis virus (which requires the availability of anti-HDV IgG and IgM serological tests).
HCV is classified in the family Flaviviridae. Like other flaviviruses, HCV is an enveloped RNA virus with an inner nucleoprotein core. Its envelope contains two glycoproteins, E1 and E2, which form heterodimers (to form a functional subunit) at the surface of the virion. Efforts to isolate the virus by standard immunological and virological techniques were unsuccessful and HCV was finally identified by direct cloning and sequencing of its genome. Although the virus was identified 25 years ago (in 1989) (Choo et al. 1989), its replication cycle is still not fully understood. An important feature of HCV is that the viral genome displays extensive genetic heterogeneity at the local as well as the global level. Even within a host, the HCV genome population circulates as a ‘quasi-species’ of closely related sequences. Worldwide, a high degree of genetic variation exists, resulting in at least six major genotypes and more than 100 distantly related subtypes (Forns and Bukh 1999). It has been reported that virus pathogenicity and sensitivity to current standards of treatment appear to vary with different subtypes (genotypes 2 and 3, responding better than genotype 1 and 4). These characteristics of HCV, much like HIV, make it a moving target for vaccine design.
HCV is a major cause of acute hepatitis and chronic liver disease, including cirrhosis and HCC. Globally, an estimated 150 million persons are infected with HCV and more than 350,000 people are estimated to die from HCV-related liver diseases (Alter 2007; WHO 2012). The worldwide prevalence of HCV-infected people ranges from 1 per cent in high-income countries to around 10 per cent in low- and middle-income countries (Fig. 8.16.2). Table 8.16.1 summarizes the global prevalence and mortality of HCV versus the observed prevalence and mortality of HBV and HIV/AIDS.
The reported seroprevalence in the Nile delta ranges from 19 per cent in the 10–19-year-old age group to 60 per cent in the 30-year-old age group, and is associated with a high prevalence of liver cirrhosis in Egypt. The higher prevalence in the Nile delta is reported to be linked to parenteral anti-schistosomiasis therapy, which was carried out with inadequately sterilized injection material (Frank et al. 2000). Current estimates in the United States are that 3.9 million Americans are chronically infected with HCV, with prevalence rates as high as 8–10 per cent in African Americans. Haemodialysis patients, haemophiliacs, drug addicts, and people transfused with blood before 1990 are particularly affected by the disease. In Europe, 0.1–3.3 per cent of the population has been infected, with the highest prevalence observed in Southern Europe (Italy and Romania) (Blachier et al. 2013).
Despite infection control precautions, healthcare providers remain at risk for acquiring blood-borne viral infections due to accidental exposure. Therapeutic injections are reported as accounting for 2 million new HCV infections each year. Many of these injections are performed in less than ideal conditions, often with reuse of needles or multidose vials and mainly, but not exclusively, in low- and middle-income countries. The residual risk of transmitting HCV through blood transfusion is very low in industrialized countries but safety of blood supply remains a major source of public concern in low- and middle-income countries.
Up to 60–70 per cent of intravenous drug users living in urban areas are seropositive for HCV antibodies. The rate of infection depends on the length of drug use, with 25 per cent of infections occurring during the first year of addiction, 50 per cent after 5 years, and up to 90 per cent after more than 5 years of intravenous drug use.
The global epidemic of HCV infection emerged in the second half of the twentieth century and has been attributed, at least in part, to the increasing use of parenteral therapies and blood transfusion during that period. In high-income countries, the rapid improvement of healthcare conditions and the introduction of anti-HCV screening for blood donors have led to a sharp decrease in the incidence of iatrogenic HCV (Prati 2006). Injectable drug use remains the main route of transmission, accounting for nearly 90 per cent of new HCV infections. Mother-to-child transmission has been widely documented. The risk of perinatal infection in children from HCV-infected mothers ranges from 3 per cent to 10 per cent in different populations. Transmission is believed to occur in utero, as a consequence of a high viral load in the mother (in particular, from mothers who are HIV-co-infected) (Kato et al. 1994). There is no contraindication for infected mothers to breastfeed the newborn. Sexual transmission is thought to be relatively infrequent (2–3 per cent); as such, it is not recommended in monogamic and stable couples to use condoms. However, the large reservoir of HCV carriers provides multiple opportunities for exposure to potentially infected partners. Individuals with multiple sexual partners, male homosexuals, prostitutes and their clients, patients with common sexually transmitted infections, and partners of HCV and HIV co-infected persons are at the highest risk of acquiring HCV sexually.
In many cases of HCV infection, no recognizable transmission factor or route is identified (Memon and Memon 2002).
The incubation period for hepatitis C before the onset of clinical symptoms ranges from 6 to 7 weeks on average. In acute infections, the most common symptoms are fatigue and jaundice; however, the majority of cases (between 60 and 70 per cent), even those who develop chronic infection, are asymptomatic for years. Fulminant hepatitis C forms are very rarely observed. While most patients with acute HCV infection have mild symptoms or no symptoms, 50–85 per cent of those infected develop chronic disease. Chronic disease is difficult to recognize because symptoms are mild and infection passes silently and insidiously from the acute to the chronic phase. Serological diagnosis of acute HCV infection is mainly based on recent HCV antibodies (anti-HCV) seroconversion. Persistence of HCV infection is diagnosed by the presence of HCV RNA in the blood for at least 6 months. The mechanisms of HCV persistence are currently unknown, although it is known that HCV chronicity develops despite humoral and cellular responses to HCV proteins. Factors associated with development of chronic disease appear to include older age at the time of infection, male gender, and an immunosuppressed state such as HIV infection (Lauer and Walker 2001).
Extra-hepatic manifestations of hepatitis C
Hepatitis C virus infection provokes dysfunction in B-lymphocytes with extra-hepatic manifestations of autoimmunity.
Many autoimmune and metabolic diseases have been associated with HCV infection: lichuen planus, granuloma annulare, porphyria cutanea tarda, and psoriasis (Andrade et al. 2012). The most important expression of autoimmunity in HCV carriers is HCV-related cryoglobulinaemia, which can cause purpura, vasculitis, glomerulonephritis, and peripheral neuropathy (Atta et al. 2010). A higher level of cryoglobulinaemia has been found in HCV carriers with lymph proliferative disorders, mainly B-cell non-Hodgkin lymphoma (Yu and Lin 2013).
Furthermore, HCV infection has been associated with higher risk of insulin resistance and diabetes (Naing et al. 2013). On the other side diabetes is a confirmed risk factor for the evolution to hepatocellular carcinoma.
The presence of non-organ specific autoantibodies is another expression of autoimmunity found in HCV carriers, which has been associated in some studies with advanced fibrosis and failure in the treatment of hepatitis C with the combined therapy of interferon-α plus ribavirin. Antibodies to self-antigens such as nucleoproteins (ANA), smooth muscle (SMA), liver–kidney microsomal type-1 antigen (LKM-1), immunoglobulin G (RF), neutrophil cytoplasm (ANCA), and phospholipids (APL), which are routinely used as biomarkers of autoimmune diseases, can be found in HCV-carriers with varying prevalence. Their induction seems mainly to involve immune cross-reactions caused by molecular mimicry between HCV polyprotein and human auto antigens (Atta et al. 2010).
The primary goals for treatment of HCV infection are to reduce morbidity and mortality through complete clearance of HCV and normalization of liver enzymes, reducing disease progression, improving quality of life, and reducing the reservoir of chronic carriers, thereby controlling further transmission. In contrast with hepatitis B, chronic HCV infection is potentially curable. Virological cure or sustained viral response is defined by the persistence of negativity of HCV-RNA 6 months after ending therapy.
Treatment is recommended for patients with an increased risk of developing cirrhosis or with potential harmful extra-hepatic manifestations of HCV; most of these patients (but not all) have persistently elevated liver enzymes.
In patients with cirrhosis, the benefits of therapy will be: reduction of the risk of decompensation, reduction of the risk of evolution to hepatocellular carcinoma, and reduction of the risk of dying from a liver-related death (Veldt et al. 2007).
Effective sustained viral response has been obtained in about 50 per cent of HCV patients with genotype 1 and 80 per cent of patients with genotypes 2 or 3 who had received combined weekly pegylated interferon-based treatment with daily ribavirin for 48 weeks (Chevalier and Pawlotsky 2007; Tan and Lok 2007). This negativity of HCV-RNA 6 months after the end of therapy is maintained in 99 per cent of all patients.
More recently, the introduction of new drugs (boceprevir and telaprevir) in the HCV therapeutic schedule, increased the chance of sustained viral response (SVR) to 70 per cent in naive patients and to almost 80 per cent in patients who relapsed after the standard treatment with peginterferon + ribavirin. However, the triple therapy seems to have more adverse events, namely anaemia in boceprevir and anaemia and cutaneous rash in telaprevir (Jacobson et al. 2011; Kwo et al. 2010).
The therapy for chronic HCV is too costly for most patients in low- and middle-income countries to afford. The new drugs make the treatment cost higher, even for industrialized countries. Besides, the adverse events during treatment require multidisciplinary medical care and personnel with solid expertise to manage this treatment. Unfortunately, they are not available in most countries.
There are new oral and more specific drugs arriving, without the need for interferon or even ribavirin. They inhibit several regions of HCV (e.g. polymerase) having an efficacy estimated to be around 80–90 per cent in 12 weeks of therapy (Suzuki et al. 2012).
Public health impact
HCV has been compared to a ‘viral time bomb’. The WHO estimates that about 150 million people, that is, some 2 per cent of the world’s population, are infected with HCV; 75–80 per cent of them are chronic HCV carriers at risk of developing liver cirrhosis and/or HCC. It is estimated that 3–4 million persons are newly infected each year and that 20 per cent of those infected with HCV progress to cirrhosis within the first 10 years after infection (Alter 2007; Gerberding and Henderson 1992). Although the prevalence of chronic HVC reached a peak in 2001 (according to a multiple cohort model) in the United States, the prevalence of hepatitis C cirrhosis and its complications will continue to increase through the next decade (Davis et al. 2010). In Europe the prevalence of chronic hepatitis C in the last decade was 0.13–3.26 per cent. It is of great concern that about 90 per cent of people in Europe infected by viral hepatitis are unaware of their status (Blachier et al. 2013). Furthermore, chronic HCV disease is the primary indication for liver transplantation in industrialized countries (Adam et al. 2012).
There is no vaccine against HCV. Research is in progress, but the high mutability of the HCV genome complicates vaccine development. Although 20–35 per cent of patients with acute HCV infection clear the virus spontaneously, lack of knowledge of any protective immune response following HCV infection impedes vaccine research. Although some studies have shown the presence of virus-neutralizing antibodies, it is not fully clear whether and how the immune system is able to eliminate the virus. Thus, from a global perspective, the greatest impact on HCV disease burden will likely be achieved by focusing efforts on reducing the risk of HCV transmission from nosocomial exposures (e.g. screening of blood, rigorous implementation of infection control, reducing unsafe injection practices) and high-risk behaviours (e.g. injection drug use).
Adherence to fundamental infection control principles, including safe injection practices and appropriate aseptic techniques, is essential to prevent transmission of blood-borne viruses in healthcare settings. Educational programmes aimed at the prevention of drug use and, for those already addicted, aimed at the prevention of shared needles and other equipment can decrease this source of infection. Some countries have established needle exchange programmes that provide easy access to sterile needles and syringes, accompanied by counselling and health education and instructions on the safe disposal of used syringes.
Alcoholic liver disease
Alcoholic beverages have been used in human societies since the beginning of recorded history. In 2005, a study estimated that just over 40 per cent of the world’s adult population consumes alcohol and the average consumption per drinker is 17.1 L per year (Shield et al. 2013).
It has long been known that alcohol consumption is responsible for increased illness and death. Worldwide, alcohol causes 2.5 million deaths each year, including 320,000 young people between the age of 15 and 29 (9 per cent of deaths in that age group) and 693 million (4.5 per cent of total) disability-adjusted life years (DALYs) (WHO 2011a, WHO 2011b). The burden is not equally distributed among countries. The highest disease load attributable to alcohol is found in the heavy-drinking former socialist countries of Eastern Europe and in Latin America (Fig. 8.16.3). For most diseases there is a dose–response relation to the volume of alcohol consumption, with the risk of the disease increasing with higher volume.
Alcoholic liver disease, resulting from the chronic and excessive consumption of alcoholic beverages, represents a considerable burden for the practising clinician, constituting the commonest reason for admitting patients with liver disease to a hospital. Alcohol (37 per cent), viral hepatitis (39 per cent), or both (4 per cent) are the leading indications for liver transplantation following cirrhosis, representing 57 per cent of transplants in Europe (European Liver Transplant Registry 2011) (Fig. 8.16.4), and alcohol is responsible for 50 per cent of deaths due to liver cirrhosis (WHO 2011c).
The costs to society from alcohol abuse cannot be overemphasized. In 2006, overall costs in the United States reached US$223.5 billion, out of which healthcare expenses accounted for 11 per cent. Almost three-quarters of these costs were due to binge drinking (Bouchery et al. 2011). Despite this burden, surprisingly little consensus exists on disease pathogenesis and on the factors that determine susceptibility.
Worldwide patterns of alcoholic intake and burden of disease in general and alcoholic liver disease in particular
Patterns of alcohol intake are constantly evolving as well as the prevalence and incidence of alcoholic liver disease. In 2010, 5.5 per cent of the global burden of disease was attributable to alcohol. This is almost as much as the burden of disease from tobacco (6.3 per cent) (Lim et al. 2012). Alcohol use represented the leading risk factor for global disease burden in Eastern Europe, most of Latin America, and southern sub-Saharan Africa. Given the relationship between alcohol consumption and cirrhosis (Sheron et al. 2008), it would be expected that there is a lag period between changes in per capita alcohol consumption and cirrhosis-related mortality. Data regarding this lag effect have been conflicting. In fact, a long latency time is not observed, and the usual lag period is only one year or less (Kerr et al. 2000).
Morphology and natural history of alcoholic liver disease
Fatty liver (steatosis)
The first and most predictable hepatic change attributable to alcohol is the development of large droplet (macrovesicular) steatosis. This disorder usually resolves within 2 weeks if alcohol consumption is discontinued (Diehl 1997). In the past, it was assumed that alcoholic fatty liver was a benign process. However, it is now assumed that 5–15 per cent of patients will develop cirrhosis during a 10-year follow-up period (Sorensen et al. 1984).
The spectrum of alcoholic steatohepatitis includes fatty infiltration of hepatocytes associated with hepatocellular injury including ballooning degeneration, Mallory bodies inflammation with neutrophils and/or lymphocytes, and fibrosis with a perivenular, perisinusoidal, and pericellular disposition. These changes are present in 10–35 per cent of all alcoholics. It is not a benign process. Some patients will develop fatal decompensation. In addition, the risk of developing cirrhosis is increased. It is estimated that the probability of developing cirrhosis is 10–20 per cent per year and 70 per cent of patients with alcoholic hepatitis will eventually develop cirrhosis (Diehl 1997).
The main causes for cirrhosis are: HBV (worldwide), HCV (in Europe), and alcohol (Cortez-Pinto et al. 2010). In 2010, more than 1 million deaths (2 per cent of all deaths) were due to liver cirrhosis. Alcoholic cirrhosis accounts for 48 per cent of cirrhosis-related deaths (Rehm et al. 2013). The long-term prognosis of alcoholic cirrhosis improves with abstinence. The 5-year survival in compensated cirrhosis patients who continue to drink is 70 per cent, but can be as high as 90 per cent if they abstain from further alcohol intake. In patients with decompensated cirrhosis, the 5-year survival drops to 30 per cent in individuals who continue to drink, but is 60 per cent in those who stay abstinent (Alexander et al. 1971; Diehl 1997).
Alcohol can be considered both as a primary cause of HCC and as a co-factor for the development of HCC. Most of the studies on incidence of HCC in alcoholic cirrhosis date from before the identification of the HCV. As hepatitis C is relatively frequent in alcoholics, the proportional contribution of alcohol in the reported HCC incidence rates in earlier studies is likely to be overestimated. Although the exact annual incidence rate of HCC in alcoholic cirrhosis is unknown, it is estimated to be over 1.5 per cent, making it worthwhile to offer patients testing (Bruix and Sherman 2005).
Factors influencing the risk of alcoholic liver disease
Most authors agree that persons who drink heavily (50–60 g of ethanol daily) represent a population at increased risk of developing liver disease (Becker et al. 2002). However, the absolute risk of acquiring alcoholic hepatitis or cirrhosis is relatively low (6.9 per cent in the mentioned study). This suggests that genetic factors and/or environment play a role in disease risk. Many studies that address the risk factors refer to their effect on ‘alcoholic liver disease’ in general rather than any specific aspect of alcoholic liver disease such as steatohepatitis.
Amount of alcohol
There is a general agreement that excessive alcohol consumption is associated with an increased risk of cirrhosis. However, the exact dose or a specific dose–response relationship for cirrhosis has not been agreed on. Evidence suggests that there is an increased risk for alcoholic liver disease with the ingestion of 60–80 g/day of alcohol in men and 20 g/day in women (Day 2000). ‘Safe’ limits of alcohol consumption for the liver are up to one–two drinks per day for women, and up to three–four drinks per day for men, with at least three alcohol-free days per week (European Association for the Study of the Liver 2012; Michielsen and Sprengers 2003).
Researchers from Denmark showed in a large survey of 30,630 persons that beer or spirits are more likely to promote liver disease than wine (Becker et al. 2002). At present, it is uncertain whether wine per se is responsible for this reduced risk of liver disease compared to the other alcoholic beverages, or whether it represents a surrogate for other healthy behaviours such as increased consumption of fruits/vegetables (Everhart 2003).
Binge-drinking, a mode of social behaviour nowadays, is the exaggerated form of non-mealtime drinking. It has been reported to increase the risk of alcoholic hepatitis fivefold (Barrio et al. 2005), and to increase the risk of all-cause mortality in men and women (Tolstrup et al. 2004). Also drinking multiple types of alcohol has been shown to be related to the risk of cirrhosis and non-cirrhotic liver disease (Naveau et al. 1997).
It is well recognized that women are more susceptible to alcohol-induced health disorders than men. Men and women have similar sized livers and when the rate of alcohol metabolism is normalized to liver mass, men and women have similar metabolic rates. However, blood alcohol levels after comparable doses of alcohol will usually be higher in women than in men because of their lower body volume and the higher percentage of their body mass consisting of fat. Evidence from animal models has suggested that oestrogen increases the gut permeability to endotoxin and accordingly upregulates endotoxin receptors of Kupffer cells leading to an increased production of tumour necrosis factor alpha in response to endotoxin (Enomoto et al. 1999). It is also known that the gastric alcohol dehydrogenase activity can be different in men and women (Parlesak et al. 2002).
Individuals with co-morbid conditions affecting the liver exhibit a greater tendency to develop liver disease in response to alcohol consumption than persons being otherwise healthy (Fattovich et al. 2004). This was clearly demonstrated in the case of hepatitis C (Corrao and Arico 1998), hepatitis B, hereditary haemochromatosis (Fletcher et al. 2002), and obesity (Naveau et al. 1997) and most probably applies to other causes of chronic hepatitis.
Non-alcoholic fatty liver disease and non-alcoholic steatohepatitis
Steatosis is defined as the accumulation of fat in the liver parenchymal cells or hepatocytes. A distinction is made between macrovesicular and microvesicular steatosis. Macrovesicular steatosis implies the presence of large fat vacuoles, containing predominantly triglycerides, and occupying a large part of the cell cytoplasm, displacing the nucleus towards the cell border. The hepatocytes may be enlarged by the presence of these fat vacuoles. Macrovesicular steatosis is graded according to the percentage of hepatocytes containing fat vacuoles: less than 5 per cent is minimal or no steatosis; 5 to 30 per cent is mild steatosis; over 30 to 60 per cent is moderate; and greater than 60 per cent is considered to be severe macrovesicular steatosis (D’Allessandro et al. 1991). In microvesicular steatosis, bipolar lipids are forming micelles, which are spread over the cytoplasm, and which do not displace the nucleus. The cells usually have normal dimensions. Grading is less complex: 45 per cent is considered to be severe microvesicular steatosis (Sheiner et al. 1995). In many patients, both types of steatosis are present, called mixed type steatosis. In those cases, macrovesicular steatosis is usually predominant.
Two terms have been used interchangeably in the past two decades to describe fat accumulation in hepatocytes. These include non-alcoholic fatty liver (NAFL) and non-alcoholic fatty liver disease (NAFLD). While NAFL has been linked to constitutional fatty infiltration of hepatocytes, which is not necessarily associated with an inflammatory response or fibrosis, NAFLD has been linked to an active hepatic injury pattern, inflammation and fibrosis. However, there is no consensus regarding the use of these two terms and the distinction between them. Regardless, in NAFL or NAFLD, steatosis is present, and alcohol is excluded as a cause of the steatosis (Harrison et al. 2004). The maximum daily alcohol consumption allowed for the definition of NAFLD is 10 g (Byrne and Wild 2010). The diagnosis of alcohol consumption relies on thorough anamnesis and hetero-anamnesis, with a detailed 7-day diary of alcohol use. Laboratory parameters are non-specific and even carboxy-deficient transferrin measurement is not very accurate in excluding significant alcohol consumption. In addition, the differential diagnosis cannot be made histologically, as the histological features of alcoholic and non-alcoholic liver disease seem to be identical. The diagnosis of the aspect of ‘non-alcoholic’ therefore constitutes a first problem in the interpretation of any data on the prevalence and natural history of NAFLD.
Non-alcoholic steatohepatitis (NASH) is a subgroup of NAFLD, in which liver steatosis is accompanied by signs of liver cell damage (especially ballooning of hepatocytes) and/or inflammation. In these patients, fibrous tissue may be generated, and patients can evolve to cirrhosis and its complications, including HCC. Although still debated, it is generally believed that pure steatosis does not lead to fibrogenesis, but steatosis is a sine qua non condition to NASH. NASH patients are more likely to have progressive liver disease (Angulo 2002).
Although not reflected by the name, NAFLD also implies the exclusion of other chronic liver diseases, including chronic viral hepatitis, toxic hepatitis (due to industrial toxins or solvents or to pharmacological agents), autoimmune liver disease, haemochromatosis, Wilson’s disease, and some rare metabolic disorders. Hepatitis C, especially genotype 3, and Wilson’s disease are two classical examples of liver diseases accompanied by steatosis, but they are not NAFLD. As will be discussed further, steatosis is no longer regarded as an innocent bystander, therefore the term NAFLD is preferred over NAFL.
A first problem is the diagnosis of the aspect ‘non-alcoholic’. Patients may not accurately report the quantity of alcohol they consume. Laboratory tests, including elevation of AST (aspartate transaminase) more than ALT (alanine transaminase), elevation of γ-GT (gamma-glutamyl transpeptidase) or CDT (carboxy-deficient transferrin) measurement may be helpful, but are inaccurate. Thorough anamnesis and hetero-anamnesis is the cornerstone of the diagnosis, which therefore may always remain questionable.
A second problem is the diagnosis of steatosis and steatohepatitis. Abdominal ultrasound has a sensitivity of 70–75 per cent and a specificity of 60–70 per cent in diagnosing moderate to severe steatosis (Bellentani et al. 2000). Computed tomography scanning and magnetic resonance imaging are equally specific (100 per cent) and sensitive (75 per cent) in making the same distinction (Rinella et al. 2001). These non-invasive tools are thus not very sensitive, not able to accurately grade the steatosis, and not able to diagnose the presence of inflammation or fibrosis, and hence do not distinguish between NAFLD and NASH. Magnetic resonance spectroscopy can accurately quantify the fat content of a liver sample, but the need for specific software and practical considerations limits its use to specific research centres. Scores based on laboratory parameters are not validated for the diagnosis of steatosis (Miele et al. 2007). The gold standard for the diagnosis still is liver biopsy. The invasive character of that procedure, however, limits its use on a larger scale.
The diagnosis of steatohepatitis is even more complicated. Laboratory tests, especially the elevation of aminotransferase levels, are inaccurate, although frequently regarded as a sign of liver cell damage and hence inflammation. Patients with elevated liver tests may have pure steatosis without inflammation on liver biopsy, and 50 per cent of the patients with biopsy-proven steatohepatitis have normal transaminases (Prati et al. 2002). The cut-off values for normal aminotransferase levels have recently been questioned, and lowering the upper limit of normal to 30 U/L in males and 19 U/L in females increases the sensitivity for the diagnosis of NASH from 42 per cent to 80 per cent, but specificity decreases from 80 per cent to 42 per cent (Kunde et al. 2005). Scoring systems based on laboratory parameters have been studied and need further validation. Imaging cannot distinguish steatosis from steatohepatitis. Again, liver biopsy is the gold standard. This also holds true for the diagnosis of fibrosis. Laboratory parameters are not useful, except for a stage of cirrhosis, where more specific laboratory features can be present. Imaging is not useful for the staging of fibrosis, and is only of value if signs of cirrhosis indicate advanced liver disease. Elastography, an ultrasound-based technique measuring liver stiffness (Ganne-Carrie et al. 2006), has been validated in hepatitis C, but not in NASH, and, like laboratory scoring systems, only roughly distinguishes between no or mild versus severe fibrosis and cirrhosis. Also for fibrosis, liver histology is still the gold, or at least the best, standard (Miele et al. 2007). More data are needed to approve elastography (Fibroscan®) or other non-invasive methods for clinical assessment of NASH (Friedrich-Rust et al. 2010).
Prevalence of steatosis, NAFLD, and NASH
As already mentioned, the difficulty in diagnosing non-alcoholic steatosis, and the lack of accuracy of the tools for the diagnosis of steatosis, constitute two major problems in the acquisition of precise epidemiological data. Sample selection constitutes a third problem, as some categories of patients are more at risk. In screening studies with ultrasound, prevalence varies between 16 and 23 per cent (Bellentani et al. 2000). In an autopsy series of traffic accidents, steatosis was histologically diagnosed in 24 per cent of cases. The prevalence was clearly age related: in those aged 20 years, the prevalence was 1 per cent, while in those aged 60 years the prevalence rose to 39 per cent (Hilden et al. 1997). Based on these figures, and making the distinction with alcoholic steatosis, the prevalence of non-alcoholic steatosis is estimated at 15–20 per cent in the general adult population (Angulo 2002). Exact data on the prevalence of NASH in the general population are scarce. In an autopsy series, a prevalence of 6.3 per cent was reported. The prevalence is usually estimated at 2 per cent, but this highly depends on sample selection. As a number of risk factors can be identified (see following subsections), prevalence rates may vary geographically (Neuschwander-Tetri and Caldwell 2003).
NAFLD and NASH and the metabolic syndrome
The metabolic syndrome, associating visceral overweight, dyslipidaemia, hyperinsulinaemia or diabetes mellitus, and arterial hypertension, as defined by the Third Report of the National Cholesterol Education Expert Panel on Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (Adult Treatment Panel-ATP III) (Expert Panel 2001), seems to be closely related with NAFLD and NASH. Some authors consider NAFLD and NASH as the hepatic manifestation of the metabolic syndrome. Many epidemiological data support a close relationship between the two entities.
In patients with NAFLD, the metabolic syndrome, according to the criteria of the ATP III (Table 8.16.2), is fully present in 30 per cent of males and 60 per cent of females. Visceral adiposity is present in 40 per cent and 65 per cent of males and females, respectively, and diabetes in 10 per cent and 30 per cent, respectively. These prevalence rates are significantly higher than in the control population. The metabolic syndrome is significantly more prevalent in patients with NASH compared to patients with simple steatosis (38 per cent vs 14 per cent, p = 0.004) (Marchesini et al. 2003).
Table 8.16.2 Diagnosis of metabolic syndrome according to ATP III
Central obesity (waist circumference):
> 102 cm
> 88 cm
≥ 150 mg/dL
High-density lipoprotein cholesterol:
< 40 mg/dL
< 50 mg/dL
Arterial blood pressure
≥ 130/ ≥ 85 mmHg
≥ 100 mg/dL
In patients with obesity, steatosis is present in 60–95 per cent, according to the selection of patients and the procedure used for diagnosis (e.g. ultrasound or histology in a series of patients undergoing bariatric surgery). The body mass index (BMI) is an independent predictive factor for the accumulation of fat in the liver (Marchesini et al. 2003).
Globally, the prevalence of overweight and obesity has increased since 1980, and the increase has accelerated. The global age-standardized prevalence of obesity nearly doubled from 6.4 per cent in 1980 to 12.0 per cent in 2008. Half of this rise occurred in the 8 years between 2000 and 2008 (Stevens et al. 2012). This increase of the prevalence of overweight in children and adolescents is of particular concern. The prevalence of diabetes is also increasing, and was estimated at around 9 per cent worldwide in 2008 (Danaei et al. 2011). In the United States, 22 per cent of the adult population fulfils the criteria of the metabolic syndrome (Lin and Pi-Sunyer 2007).
The natural history of NAFLD/NASH
Data on the natural history of NAFLD and NASH have the same three problems as outlined for the prevalence data. In patients with NASH, 45 per cent will exhibit fibrosis progression and 19 per cent will ultimately develop cirrhosis (Fassio et al. 2004). In patients with NAFLD, lifetime progression to cirrhosis is estimated at 2–5 per cent (Dam-Larsen et al. 2004; Ekstedt et al. 2006).
It is not clear whether only NASH patients will progress, or if pure steatosis may also lead to progressive fibrosis and ultimately cirrhosis. A long-term follow-up study (mean follow-up of 13.7 years) showed no increase in mortality in patients with elevated liver enzymes and pure steatosis on an initial biopsy. Patients with biopsy-proven NASH, on the other hand, had a higher risk of dying from cardiovascular disease (15.5 per cent vs 7.5 per cent, p = 0.04) and from liver-related causes (2.8 per cent vs 0.2 per cent, p = 0.04). Disease progression was, however, noted: 41 per cent had fibrosis progression and 5.4 per cent of patients developed cirrhosis, and this did not depend on features of inflammation on the initial biopsy (Ekstedt et al. 2006).
In patients with cryptogenic cirrhosis, more than 60 per cent have features that might have been associated with NASH and in these patients cirrhosis is believed to be an end stage of NASH (Ekstedt et al. 2006). Actually cryptogenic cirrhosis accounts for 8 per cent of the indications for liver transplantation in Europe (European Liver Transplant Registry 2011). NASH may recur after liver transplantation, further enforcing the concept of NASH as aetiology of cryptogenic cirrhosis (Maheshwari and Thuluvath 2006).
HCC has been reported in patients with NASH-associated cirrhosis. Data on prevalence and risk, however, are scarce. In the Ekstedt series (Ekstedt et al. 2006), 2.3 per cent developed HCC or 43 per cent of those with documented cirrhosis. It is thus not clear whether the risk is comparable to the 10 per cent cumulative risk usually reported in cirrhosis of any aetiology, but it might be higher (Smedile and Bugianesi 2005). HCC has not been reported without cirrhosis or extensive fibrosis. With the obesity epidemic, it is expected that HCC related to NASH will become more frequent (White et al. 2012).
Risk factors reported to be associated with an increased risk of fibrosis are: age (40 or 50 years of age), the presence of diabetes, BMI 25 or 28 or 30, hypertriglyceridaemia, elevated transaminases two times the upper limit of normal, and AST/ALT 1 (Angulo et al. 1999; Adams et al. 2005). Patients with NAFLD and diabetes have a higher probability of cirrhosis and liver-related death, compared to NAFLD patients without diabetes (Abrams et al. 2004). In the Ekstedt series (Ekstedt et al. 2006), the 41 per cent progression of fibrosis was associated with higher levels of ALT, a higher weight gain during follow-up, more severe insulin resistance and more pronounced fatty infiltration. As stated previously, patients with NASH more frequently meet the criteria of the metabolic syndrome and are more likely to have visceral obesity compared to patients with simple steatosis. As it is believed that NASH is a subgroup of NAFLD at risk for progressive fibrosis, the metabolic syndrome and its components clearly constitute a risk factor for fibrosis and cirrhosis, which will be a major burden of disease in view of the epidemic of obesity and diabetes and their related conditions.
No specific treatment is clearly defined for NASH, but there is a consensus concerning implementation of behavioural measures as well as treating cases of advanced disease (Chuthan Sourianarayanane et al. 2013). NASH treatment is driven by the stage of the disease. In more advanced stages, drugs must be added to classical behavioural measures. Up to now, it is clear that patients with NASH benefit from physical exercise and balanced, well oriented diets, probably through weight loss and decreased insulin-resistance (Carulli et al. 2013).
Pharmacological treatment adjuvants for weight losing may be considered in some selected cases. Orlistat and sibutramine have been used, but their indication is limited due to their adverse side effects.
Bariatric surgery is recommended in patients with a BMI greater than 40 kg/m2 or BMI greater than 35 kg/m2 and co-morbidities. This procedure is highly effective and may be indicated even in patients with well compensated cirrhosis, but it has high risk of morbidity if the patients have portal hypertension.
For patients who evolved toward advanced liver disease or HCC, liver transplantation can be indicated, although NASH relapse post transplantation is quite frequent.
Specific pharmacotherapy includes drugs used to treat metabolic syndrome, as well as drugs with putative antioxidants effects. The most prescribed drugs are insulin-sensitizers (metformin and pioglitazone). A recent meta-analysis compared the results of the studies that involved these drugs and concluded that pioglitazone is superior compared with metformin (Musso et al. 2010), but pioglitazone has been associated with potential harmful adverse events, such as heart failure and bladder cancer.
Antioxidants are considered promising drugs for NASH, but the studies are considered preliminary. Among the putative antioxidant drugs, vitamin E has been evaluated as having the most consistent results, even with documented amelioration in liver pathology (Sanyal et al. 2010). On the other hand, prolonged use of vitamin E has been associated with adverse reactions such as risk of cerebral vascular haemorrhage, coagulation disturbance and prostatic disorders.
Despite benefits observed in the above mentioned drug therapies, the long-term use of these drugs on NASH in terms of efficacy and safety remains unknown.
In spite of the availability of safe and effective vaccines and their proven effectiveness in reducing the chronic consequences of HBV infections, the current burden of disease associated with hepatitis B remains substantial. To finally achieve the WHO goal of HBV elimination, continuous efforts will be required to keep prevention of hepatitis B on the agenda of public health officers worldwide, and to continue to improve treatment options for those already suffering chronic hepatitis B.
Even if the present burden of disease caused by hepatitis C is somewhat less impressive, the lack of an effective vaccine despite major efforts in its development, and the increased burden of chronic liver disease resulting from the high rates of HCV infection 20–30 years ago (the baby boomer generation, born 1946–1964), pose a substantial future threat to public health.
Alcoholic liver disease remains a major cause of morbidity and mortality worldwide. There is concern that, worldwide, alcoholic liver disease may increase in the next several decades. Recent data indicate that alcohol consumption is increasing in low- and middle-income countries. In addition, rates of excessive alcohol intake appear to be rising in women and binge drinking has become a common pattern of excessive alcohol use. Although alcohol-related cirrhosis mortality rates decreased in many countries during the past 30 years, rates are no longer declining in several countries and are actually increasing in low- and middle-income countries.
Although data on the prevalence and natural history of NAFLD/NASH are scarce and suffer from multiple methodological problems, it is clear that, because of their association with the metabolic syndrome and its components, which are increasing to epidemic proportions in the Western population, NAFLD and NASH will constitute a major health problem in the near future.
◆ Liver cirrhosis and primary liver cancer are important public health problems worldwide, killing more than 1 million people each year. Liver cancer is the third most common cause of deaths from cancer.
◆ Viral hepatitis B and C, and alcoholic as well as non-alcoholic fatty liver disease, represent the major causes for chronic liver diseases. All have oncogenic potential.
◆ Despite the availability and widespread use of effective hepatitis B vaccines, efforts will be required to keep the immunization programmes on the political and donor agenda.
◆ As the development of a hepatitis C vaccine has not yet resulted in success, prevention and control measures will form a major challenge to all those involved in public health. Easy and equal access to the new antiviral treatments is of the utmost importance.
◆ In low- and middle-income countries experts predict a future wave of alcohol-related liver diseases.
◆ Fatty liver disease and steatohepatitis and chronic liver diseases associated with the metabolic syndrome, may rise to epidemic proportions in the near future in Western populations.
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