Jawetz Chapter 35: Hepatitis Viruses PDF

35 C H A P T E R Hepatitis Vir...

35 C H A P T E R Hepatitis Viruses Viral hepatitis is a systemic disease primarily involving the 5 minutes, dry heat (180°C for 1 hour), ultraviolet irradiation liver. Most cases of acute viral hepatitis in children and adults (1 minute at 1.1 watts), treatment with formalin (1:4000 for are caused by one of the following five agents: hepatitis A virus 3 days at 37°C), or treatment with chlorine (10–15 ppm for (HAV), the etiologic agent of viral hepatitis type A (infectious 30 minutes). Heating food to above 85°C (185°F) for 1 minute hepatitis); hepatitis B virus (HBV), which is associated with and disinfecting surfaces with sodium hypochlorite (1:100 viral hepatitis B (serum hepatitis); hepatitis C virus (HCV), dilution of chlorine bleach) are necessary to inactivate HAV. the agent of hepatitis C (common cause of posttransfusion The relative resistance of HAV to disinfection procedures hepatitis); hepatitis D (HDV), a defective virus dependent on emphasizes the need for extra precautions in dealing with coinfection with HBV; or hepatitis E virus (HEV), the agent of hepatitis patients and their products. enterically transmitted hepatitis. Additional well-characterized HAV initially was identified in stool and liver prepara- viruses that can cause sporadic hepatitis, such as yellow fever tions by using immune electron microscopy (Figure 35-1). virus, cytomegalovirus, Epstein-Barr virus, herpes simplex Sensitive serologic assays and polymerase chain reaction virus, rubella virus, and the enteroviruses, are discussed in other (PCR) methods have made it possible to detect HAV in stools chapters. Hepatitis viruses produce acute inflammation of the and other samples and to measure specific antibody in serum. liver, resulting in a clinical illness characterized by fever, gas- Various primate cell lines will support growth of HAV, trointestinal symptoms such as nausea and vomiting, and jaun- although fresh isolates of virus are difficult to adapt and grow. dice. Hepatitis viruses cause similar appearing histopathologic Usually, no cytopathic effects are apparent. Mutations in the lesions in the liver during acute disease. viral genome are selected during adaptation to tissue culture. PROPERTIES OF HEPATITIS VIRUSES Hepatitis Type B The characteristics of the five known hepatitis viruses are HBV is classified as a hepadnavirus (Table 35-3). HBV estab- shown in Table 35-1. Nomenclature of the hepatitis viruses, lishes chronic infections, especially in those infected as antigens, and antibodies is presented in Table 35-2. infants; it is a major factor in the eventual development of liver disease and hepatocellular carcinoma in those individuals. Hepatitis Type A A. Structure and Composition HAV is a distinct member of the picornavirus family (see Electron microscopy of hepatitis B surface antigen (HBsAg)- Chapter 36). HAV is a 27- to 32-nm spherical particle with positive serum reveals three morphologic forms (Figures 35-2 cubic symmetry containing a linear single-stranded RNA and 35-3A). The most numerous are spherical particles genome with a size of 7.5 kb. It is assigned to picornavirus measuring 22 nm in diameter (Figure 35-3B). These small genus, Hepatovirus. Only one serotype is known. There is particles are made up exclusively of HBsAg—as are tubular no antigenic cross-reactivity with the other hepatitis viruses. or filamentous forms, which have the same diameter but may Genomic sequence analysis of a variable region involving the be more than 200 nm long—and result from overproduc- junction of the 1D and 2A genes divided HAV isolates into tion of HBsAg. Larger, 42-nm spherical virions (originally seven genotypes. Important properties of the family Picorna- referred to as Dane particles) are less frequently observed (see viridae are listed in Table 36-1. Figure 35-2). The outer surface, or envelope, contains HBsAg HAV is stable to treatment with 20% ether, acid (pH 1.0 and surrounds a 27-nm inner nucleocapsid core that contains for 2 hours), and heat (60°C for 1 hour), and its infectivity hepatitis B core antigen (HBcAg) (Figure 35-3C). The vari- can be preserved for at least 1 month after being dried and able length of a single-stranded region of the circular DNA stored at 25°C or for years at −20°C. The virus is destroyed genome results in genetically heterogeneous particles with a by autoclaving (121°C for 20 minutes), boiling in water for wide range of buoyant densities. 511 Riedel_CH35_p511-p530.indd 511 04/04/19 5:04 PM  512   SECTION IV  Virology TABLE 35-1 Characteristics of Hepatitis Viruses Virus Hepatitis A Hepatitis B Hepatitis C Hepatitis D Hepatitis E Family Picornaviridae Hepadnaviridae Flaviviridae Unclassified Hepeviridae Genus Hepatovirus Orthohepadnavirus Hepacivirus Deltavirus Hepevirus Virion 27 nm, icosahedral 42 nm, spherical 60 nm, spherical 35 nm, spherical 30–32 nm, icosahedral Envelope No Yes (HBsAg-associated) Yes Yes (HBsAg-associated) No Genome ssRNA dsDNA ssRNA ssRNA ssRNA Genome size (kb) 7.5 3.2 9.4 1.7 7.2 Stability Heat and acid stable Acid sensitive Ether sensitive, Acid sensitive Heat stable acid sensitive Transmission Fecal–oral Parenteral Parenteral Parenteral Fecal–oral Prevalence High High Moderate Low, regional Regional Fulminant disease Rare Rare Rare Frequent In pregnancy Chronic disease Never Often Often Often Never Oncogenic No Yes Yes Unknown No ds, double stranded; HBsAg, hepatitis B surface antigen; ss, single stranded. TABLE 35-2 Nomenclature and Definitions of Hepatitis Viruses, Antigens, and Antibodies Component Disease of System Definition Hepatitis A HAV Hepatitis A virus. Etiologic agent of infectious hepatitis. A picornavirus, the prototype of genus Hepatovirus Anti-HAV Antibody to HAV. Detectable at onset of symptoms; lifetime persistence IgM anti-HAV IgM class antibody to HAV. Indicates recent infection with hepatitis A; positive result up to 4–6 months after infection Hepatitis B HBV Hepatitis B virus. Etiologic agent of serum hepatitis. A hepadnavirus HBsAg Hepatitis B surface antigen. Surface antigen(s) of HBV detectable in large quantity in serum; several subtypes identified HBeAg Hepatitis B e antigen. Associated with HBV nucleocapsid; indicates viral replication; circulates as soluble antigen in serum HBcAg Hepatitis B core antigen Anti-HBs Antibody to HBsAg. Indicates past infection with and immunity to HBV, presence of passive antibody from HBIG, or immune response from HBV vaccine Anti-HBe Antibody to HBeAg. Presence in serum of HBV carrier suggests lower titer of HBV Anti-HBc Antibody to HBcAg. Indicates infection with HBV at some undefined time in the past IgM anti-HBc IgM class antibody to HBcAg. Indicates recent infection with HBV; positive result for 4–6 months after infection Hepatitis C HCV Hepatitis C virus, a common etiologic agent of posttransfusion hepatitis. A flavivirus, genus Hepacivirus Anti-HCV Antibody to HCV Hepatitis D HDV Hepatitis D virus. Etiologic agent of delta hepatitis; causes infection only in presence of HBV HDAg Delta antigen (delta-Ag). Detectable in early acute HDV infection Anti-HD Antibody to delta-Ag (anti-delta). Indicates past or present infection with HDV Hepatitis E HEV Hepatitis E virus. Enterically transmitted hepatitis virus. Causes large epidemics in Asia, North and West Africa, and Mexico; fecal–oral or waterborne transmission. A hepevirus IgM anti-HEV IgM class antibody to Hepatitis E. Indicates recent infection with HEV; positive result for 4-6 months after infection Immune IG Immune globulin treatment given intravenously. Contains antibodies to HAV; no antibodies to HBsAg, HCV, or globulins human immunodeficiency virus HBIG Hepatitis B immune globulin. Contains high titers of antibodies to HBV Riedel_CH35_p511-p530.indd 512 04/04/19 5:04 PM  CHAPTER 35 Hepatitis Viruses   513 15–25 nm 42 nm HBsAg- bearing Incomplete virus particles in blood Virion 20×20–200 nm Nonionic detergent L strand Virion core 28 nm S strand with HBcAg Strong 3′ FIGURE 35-1 Electron micrograph of 27-nm hepatitis A virus detergent 5′ aggregated with antibody (222,000 ×). Note the presence of an Virion core 3′ antibody “halo” around each particle. (Courtesy of DW Bradley, 5′ Viral DNA CL Hornbeck, and JE Maynard.) Strong 3200 bp detergent The viral genome (Figure 35-4) consists of partially Soluble double-stranded circular DNA, 3200 bp in length. Different HBeAg released HBV isolates share 90–98% nucleotide sequence homology. from virion The full-length DNA minus strand (L or long strand) is com- core plementary to all HBV mRNAs; the positive strand (S or short A strand) is variable and between 50% and 80% of unit length. There are four open reading frames that encode seven polypeptides. These include structural proteins of the virion surface and core, a small transcriptional transactivator (X), and a large polymerase (P) protein that includes DNA poly- merase, reverse transcriptase, and RNase H activities. The S gene has three in-frame initiation codons and encodes the TABLE 35-3 Important Properties of Hepadnavirusesa B Virion: About 42 nm in diameter overall (nucleocapsids, 18 nm). Genome: One molecule of double-stranded DNA, circular, 3.2 kbp. FIGURE 35-2 Hepatitis B viral and subviral forms. A: Schematic In virion, negative DNA strand is full length, and positive DNA representation of three hepatitis B surface antigen (HBsAg)- strand is partially complete. The gap must be completed at containing forms that can be identified in serum from hepatitis the beginning of the replication cycle. B virus (HBV) carriers. The 42-nm spherical Dane particle can be disrupted by nonionic detergents to release the 28-nm core that Proteins: Two major polypeptides (one glycosylated) are present contains the partially double-stranded viral DNA genome. A soluble in HBsAg; one polypeptide is present in HBcAg. antigen, termed hepatitis B e antigen (HBeAg), may be released from Envelope: Contains HBsAg and lipid. core particles by treatment with strong detergent. HBcAg, hepatitis Replication: By means of an intermediate RNA copy of the DNA B core antigen. B: Electron micrograph showing three distinct genome (HBcAg in nucleus; HBsAg in cytoplasm). Both mature HBsAg-bearing forms: 20-nm pleomorphic spherical particles (A), virus and 22-nm spherical particles consist of HBsAg secreted filamentous forms (B), and 42-nm spherical Dane particles, the from the cell surface. infectious form of HBV (C). (Courtesy of FB Hollinger.) Outstanding characteristics: Family is made up of many types that infect humans and lower major HBsAg, as well as polypeptides containing in addition animals (eg, woodchucks, squirrels, and ducks). pre-S2 or pre-S1 and pre-S2 sequences. The C gene has two Cause acute and chronic hepatitis, often progressing to in-frame initiation codons and encodes HBcAg plus the HBe permanent carrier states and hepatocellular carcinoma. protein, which is processed to produce soluble hepatitis B e HBcAg, hepatitis B core antigen; HBsAg, hepatitis B surface antigen. antigen (HBeAg). a For hepatitis A virus, see properties of picornaviruses (see Table 36-1); for The particles containing HBsAg are antigenically com- hepatitis C virus, see description of flaviviruses (see Table 38-1). plex. Each contains a group-specific antigen, a, in addition Riedel_CH35_p511-p530.indd 513 04/04/19 5:04 PM  514   SECTION IV  Virology A B C FIGURE 35-3 A: Unfractionated hepatitis B surface antigen (HBsAg)-positive human plasma. Filaments, 22-nm spherical particles, and a few 42-nm virions are shown (77,000 ×). B: Purified HBsAg (55,000 ×). (Courtesy of RM McCombs and JP Brunschwig.) C: Hepatitis B core antigen purified from infected liver nuclei (122,400 ×). The diameter of the core particles is 27 nm. (Courtesy of HA Fields, GR Dreesman, and G Cabral.) to two pairs of mutually exclusive subdeterminants, d/y and in epidemiologic investigations because secondary cases have w/r. Thus, four phenotypes of HBsAg have been observed: the same subtype as the index case. adw, ayw, adr, and ayr. In the United States, adw is the pre- The stability of HBsAg does not always coincide with that dominant subtype. These virus-specific markers are useful of the infectious agent. However, both are stable at −20°C for 3155 2.1 k bR NA 3172 55 aa Pre-S2 155 8 aa 1 : 12 e-S Pr D S AN 28 prom TR 48 –S A ND Ge TR 3182/1 +S ne RE S1 G m S pr e- Pr o 40 : 22 00 Eco RI 28 0 6 aa 2450 2400 800 833 Gene C 3.5 kb R 2357 : 183 er NA 12 I 00 nc 00 Re ha aa 20 En gio X m nP DR 1 16 0 0 pr o :8 I DR2 Pre-C I 5′ Pr 3 2 e- 5′ prom E n h aa C 1621 4 181 A 01 A A 19 A 137 A 6 A 3 18 4 19 3 4 Region X : 154 aa 20 0 18 179 FIGURE 35-4 Genetic organization of the hepatitis B virus genome. Four open reading frames encoding seven peptides are indicated by large arrows. Regulatory sequences (promoters [prom], enhancers [Enh], and glucocorticoid-responsive element [GRE]) are marked. Only the two major transcripts (core/pre-genome and S mRNAs) are represented. DR1 and DR2 are two directly repeated sequences of 11 bp at the 5′ extremities of the minus- and plus-strand DNA. (Reproduced with permission from Buendia MA: Hepatitis B viruses and hepatocellular carcinoma. Adv Cancer Res 1992;59:167. Academic Press, Inc.) Riedel_CH35_p511-p530.indd 514 04/04/19 5:04 PM  CHAPTER 35 Hepatitis Viruses   515 more than 20 years and stable to repeated freezing and thaw- ing. The virus also is stable at 37°C for 60 minutes and remains viable after being dried and stored at 25°C for at least 1 week. HBV (but not HBsAg) is sensitive to higher temperatures Attachment (100°C for 1 minute) or to longer incubation periods (60°C for 10 hours). HBsAg is stable at a pH of 2.4 for up to 6 hours, Reenter cycle Exit cell but HBV infectivity is lost. Sodium hypochlorite, 0.5% (eg, 1:10 chlorine bleach), destroys antigenicity within 3 minutes Uncoating at low protein concentrations, but undiluted serum specimens require higher concentrations (5%). HBsAg is not destroyed by ultraviolet irradiation of plasma or other blood products, and viral infectivity may also resist such treatment. Host DNA repair Positive-strand DNA synthesis Transcription AAA AAA B. Replication of Hepatitis B Virus cccDNA AAA Acquire (2.1, 2.4, 3.5 kb mRNAs) envelope The infectious virion attaches to cells and becomes uncoated Nucleus (pre-Golgi) (Figure 35-5). In the nucleus, the partially double-stranded viral genome is converted to covalently closed circular double- Translation stranded DNA (cccDNA). The cccDNA serves as template for Encapsidation Cytoplasm Negative-strand all viral transcripts, including a 3.5-kb pregenome RNA. The DNA synthesis pregenome RNA becomes encapsidated with newly synthesized 3.5 kb RNA HBcAg. Within the cores, the viral polymerase synthesizes by reverse transcription a negative-strand DNA copy. The poly- FIGURE 35-5 Hepatitis B virus (HBV) replication cycle. HBV merase starts to synthesize the positive DNA strand, but the attachment to a receptor on the surface of hepatocytes occurs via a portion of the pre-S region of hepatitis B surface antigen (HBsAg). process is not completed. Cores bud from the pre-Golgi mem- After uncoating of the virus, unidentified cellular enzymes convert branes, acquiring HBsAg containing envelopes, and may exit the partially double-stranded DNA to covalent closed circular (ccc) the cell. Alternatively, cores may be reimported into the nucleus DNA that can be detected in the nucleus. The cccDNA serves as the and initiate another round of replication in the same cell. template for the production of HBV mRNAs and the 3.5-kb RNA pre- genome. The pre-genome is encapsidated by a packaging signal located near the 5′ end of the RNA into newly synthesized core Hepatitis Type C particles, where it serves as template for the HBV reverse transcriptase Clinical and epidemiologic studies and cross-challenge exper- encoded within the polymerase gene. An RNase H activity of the iments in chimpanzees in the past had suggested that there polymerase removes the RNA template as the negative-strand DNA were several non-A, non-B (NANB) hepatitis agents that, is being synthesized. Positive-strand DNA synthesis does not proceed based on serologic tests, were not related to HAV or HBV. to completion within the core, resulting in replicative intermediates The major agent was identified as HCV. HCV is a positive- consisting of full-length minus-strand DNA plus variable-length (20–80%) positive-strand DNA. Core particles containing these stranded RNA virus, classified as family Flaviviridae, genus DNA replicative intermediates bud from pre-Golgi membranes Hepacivirus. Various viruses can be differentiated by RNA (acquiring HBsAg in the process) and may either exit the cell or sequence analysis into at least six major genotypes (clades) reenter the intracellular infection cycle. (Reproduced with permission and more than 100 subtypes. Clades differ from each other from Butel JS, Lee TH, Slagle BL: Is the DNA repair system involved by 25–35% at the nucleotide level; subtypes differ from each in hepatitis-B-virus-mediated hepatocellular carcinogenesis? other by 15–25%. The genome is 9.4 kb in size and encodes Trends Microbiol 1996;4:119.) a core protein, two envelope glycoproteins, and several non- structural proteins (Figure 35-6). The expression of cDNA Structural Nonstructural 5′ UTR 3′ UTR C E1 E2 NS2 NS3 NS4B NS5A NS5B NS4A 9.4 kb HVR-1 FIGURE 35-6 Genetic organization of the hepatitis C virus genome. The single open reading frame is expressed as a polyprotein that gets processed; the positions of structural and nonstructural domains are shown. HVR-1 represents the highly variable region of an envelope glycoprotein. (Redrawn with permission from Chung RT, Liang TJ: Hepatitis C virus and hepatocellular carcinoma. In Parsonnet J [editor]. Microbes and Malignancy: Infection as a Cause of Human Cancers. Oxford University Press, 1999. Reproduced with permission of the Licensor through PLSclear.) Riedel_CH35_p511-p530.indd 515 04/04/19 5:04 PM  516   SECTION IV  Virology clones of HCV in yeast led to the development of serologic HEV or HEV-like infections in rodents, pigs, sheep, and tests for antibodies to HCV. Most cases of posttransfusion cattle in the United States, with occasional transmission NANB hepatitis were caused by HCV. to humans. Most new infections with HCV are subclinical. The majority (70–90%) of HCV patients develops chronic hepa- titis, and many are at risk of progressing to chronic active HEPATITIS VIRUS INFECTIONS hepatitis and cirrhosis (10–20%). In 1–5% of infected indi- IN HUMANS viduals, HCV leads to hepatocellular carcinoma, which is the fifth most common cause of cancer worldwide. About 25,000 Pathology individuals die annually of chronic liver disease and cirrhosis Hepatitis is a general term meaning inflammation of the liver. in the United States; HCV appears to be a major contributor Microscopically, there is spotty parenchymal cell degeneration, to this burden (∼40%). with necrosis of hepatocytes, a diffuse lobular inflammatory The virus undergoes sequence variation during chronic reaction, and disruption of liver cell cords. These parenchymal infections. This complex viral population in a host is referred changes are accompanied by reticuloendothelial (Kupffer) cell to as “quasi-species.” This genetic diversity is not correlated hyperplasia, periportal infiltration by mononuclear cells, and with differences in clinical disease, although differences cell degeneration. Localized areas of necrosis are frequently do exist in response to antiviral therapy according to viral observed. Later in the course of the disease, there is an accu- genotype. mulation of macrophages near degenerating hepatocytes. Preservation of the reticulum framework allows hepatocyte regeneration so that the highly ordered architecture of the Hepatitis Type D (Delta Hepatitis) liver lobule can be ultimately regained. The damaged hepatic An antigen–antibody system termed the delta antigen (delta- tissue is usually restored in 8–12 weeks. Ag) and antibody (anti-delta) is detected in some HBV infec- Chronic carriers of HBsAg may or may not have demon- tions. The antigen is found within certain HBsAg particles. strable evidence of liver disease. Persistent (unresolved) viral In blood, HDV (delta agent) contains delta-Ag (HDAg) hepatitis, a mild benign disease that may follow acute hepati- surrounded by an HBsAg envelope. It has a particle size of tis B in 8–10% of adult patients, is characterized by sporadi- 35–37 nm and a buoyant density of 1.24–1.25 g/mL in CsCl. cally abnormal aminotransferase values and hepatomegaly. The genome of HDV consists of single-stranded, circular, Histologically, the lobular architecture is preserved, with negative-sense RNA, 1.7 kb in size. It is the smallest of known portal inflammation, swollen and pale hepatocytes (cobble- human pathogens and resembles subviral plant pathogens (ie, stone arrangement), and slight to absent fibrosis. This lesion viroids). No homology exists with the HBV genome. HDAg is is frequently observed in asymptomatic carriers, usually does the only protein coded for by HDV RNA and is distinct from not progress toward cirrhosis, and has a favorable prognosis. the antigenic determinants of HBV. HDV is a defective virus Chronic active hepatitis features a spectrum of histo- that requires the HBsAg coat for transmission. It is often logic changes from inflammation and necrosis to collapse of associated with the most severe forms of hepatitis in HBsAg- the normal reticulum framework with bridging between the positive patients. It is classified in the Deltavirus genus, which portal triads or terminal hepatic veins. HBV is detected in is not assigned to any virus family. 10–50% of these patients. Occasionally during acute viral hepatitis, more exten- sive damage may occur that prevents orderly liver cell regen- eration. Such fulminant or massive hepatocellular necrosis Hepatitis Type E is seen in 1–2% of jaundiced patients with hepatitis B. It is HEV is transmitted enterically and occurs in epidemic 10 times more common in those coinfected with HDV than form in developing countries, where water or food sup- in the absence of HDV. plies are sometimes fecally contaminated. It was first Both HBV and HCV have significant roles in the devel- documented in samples collected during the New Delhi opment of hepatocellular carcinoma that may appear many outbreak of 1955, when 29,000 cases of icteric hepatitis (15–60) years after establishment of chronic infection. occurred after sewage contamination of the city’s drink- ing water supply. An epidemic occurred in Kashmir, India, in 1978, that resulted in an estimated 1700 deaths. Clinical Findings Pregnant women may have a high (20%) mortality rate The clinical features of infections by HAV, HBV, and HCV if fulminant hepatitis develops. The viral genome has are summarized in Table 35-4. In individual cases, it is not been cloned and is a positive-sense, single-stranded RNA possible to make a reliable clinical distinction among cases 7.2 kb in size. The virus is classified in the virus fam- caused by the hepatitis viruses. ily, Hepeviridae, in the genus Hepevirus. HEV resembles, Other viral diseases that may present as hepatitis are but is distinct from, caliciviruses. Animal strains of HEV infectious mononucleosis, yellow fever, cytomegalovirus are common throughout the world. There is evidence of infection, herpes simplex, rubella, and some enterovirus Riedel_CH35_p511-p530.indd 516 04/04/19 5:04 PM  CHAPTER 35 Hepatitis Viruses   517 TABLE 35-4 Epidemiologic and Clinical Features of Viral Hepatitis Types A, B, and C Feature Viral Hepatitis Type A Viral Hepatitis Type B Viral Hepatitis Type C Incubation period 10–50 days (average, 25–30) 50–180 days (average, 60–90) 15–160 days (average, 50) Principal age distribution Children, young adults a 15–29 years, babies b Adultsb Seasonal incidence Throughout the year but tends Throughout the year Throughout the year to peak in autumn Route of infection Predominantly fecal–oral Predominantly parenteral Predominantly parenteral Occurrence of virus Blood 2 weeks before to ≤1 week Months to years Months to years after jaundice Stool 2 weeks before to 2 weeks after Absent Probably absent jaundice Urine Rare Absent Probably absent Saliva, semen Rare (saliva) Frequently present Present (saliva) Clinical and laboratory features Onset Abrupt Insidious Insidious Fever >38°C (100.4°F) Common Less common Less common Duration of aminotransferase 1–3 weeks 1–6+ months 1–6+ months elevation Immunoglobulins (IgM levels) Elevated Normal to slightly elevated Normal to slightly elevated Complications Uncommon, no chronicity Chronicity in 5–10% (95% of Chronicity in 70–90% neonates) Mortality rate (icteric cases) 98 mon after the age of 40 years. Fulminant HBV disease is Chronic disease (%) None None associated with superinfection by other agents, including Mortality rate (%) 0.1 0.3–2.1 HDV. Most patients who survive have complete restoration of the hepatic parenchyma with normal liver function after a Adapted with permission from Hollinger FB, Ticehurst JR: Hepatitis A virus. recovery. Fulminant disease rarely occurs with HAV or HCV In Fields BN, Knipe DM, Howley PM (editors-in-chief). Fields Virology, 3rd ed. Lippincott-Raven, 1996. infections. Hepatitis C is usually clinically mild, with only minimal to moderate elevation of liver enzymes. Hospitalization is considerable overlap in timing, and the patient may not know unusual, and jaundice occurs in fewer than 25% of patients. when exposure occurred, so the incubation period is not very Despite the mild nature of the disease, 70–90% of cases useful in determining the specific viral cause. progress to chronic liver disease. Most patients are asymp- The onset of disease tends to occur abruptly with HAV tomatic, but histologic evaluation often reveals evidence of (within 24 hours) in contrast to a more insidious onset with chronic active hepatitis, especially in those whose disease is HBV and HCV. Complete recovery occurs in most hepati- acquired after transfusion. Many patients (20–50%) develop tis A cases (Table 35-5). The disease is more severe in adults cirrhosis and are at high risk for hepatocellular carcinoma than in children, in whom it often goes unnoticed. Relapses (5–25%) decades later. About 40% of chronic liver disease is of HAV infection can occur 1–4 months after initial symp- HCV related, resulting in an estimated 8000–10,000 deaths toms have resolved. annually in the United States. End-stage liver disease associ- The outcome after infection with HBV varies, ranging ated with HCV is the most frequent indication for adult liver from complete recovery to progression to chronic hepatitis transplants. and, rarely, death from fulminant disease. In adults, 65–80% of infections are inapparent, with 90–95% of all patients recovering completely. In contrast, 80–95% of infants and Laboratory Features young children infected with HBV become chronic carriers Liver biopsy permits a tissue diagnosis of hepatitis. Tests for (Table 35-6), and their serum remains positive for HBsAg. abnormal liver function, such as serum alanine aminotrans- The vast majority of individuals with chronic HBV remain ferase (ALT), aspartate aminotransferase (AST), and biliru- bin, supplement the clinical, pathologic, and epidemiologic findings. TABLE 35-6 Transmission of Hepatitis B Virus and Spectrum of Outcomes of Infection A. Hepatitis A Transmission a The clinical, virologic, and serologic events after exposure to HAV are shown in Figure 35-7. Virus particles have been Vertical Contact Parenteral, Feature (Asia) (Africa) Sexual detected by immune electron microscopy in fecal extracts of hepatitis A patients (see Figure 35-1). Virus appears early in Age at infection Newborns, Young Teenagers, the disease and disappears within 2 weeks after the onset of infants children adults jaundice. Recovery 5 20 90–95 HAV can be detected in the liver, stool, bile, and blood of from acute infection (%) naturally infected humans and experimentally infected non- human primates by immunoassays, nucleic acid hybridiza- Progression 95 80 5–10 tion assays, or PCR. HAV is detected in the stool from about to chronic infection (%) 2 weeks before the onset of jaundice up to 2 weeks after. Anti-HAV appears in the immunoglobulin M (IgM) Chronic carriersb 10–20 10–20 0.5 fraction during the acute phase, peaking about 2 weeks after (% of total population) elevation of liver enzymes (Table 35-7). Anti-HAV IgM usu- ally declines to nondetectable levels within 3–6 months. Anti- Vertical and contact-associated transmission occurs in endemic regions; HAV IgG appears soon after the onset of disease and persists a parenteral and sexual transmissions are the main modes of transmission in nonendemic regions. for decades. Thus, detection of IgM-specific anti-HAV in the b At high risk of developing hepatocellular carcinoma. blood of an acutely infected patient confirms the diagnosis Riedel_CH35_p511-p530.indd 518 04/04/19 5:04 PM  CHAPTER 35 Hepatitis Viruses   519 Virus in blood appearance of HBsAg. High concentrations of HBV particles may be present in the blood (up to 1010 particles/mL) during Virus in feces the initial phase of infection; communicability is highest at Aminotransferases this time. HBsAg is usually detectable 2–6 weeks in advance of clinical and biochemical evidence of hepatitis and persists Relative concentration of anti-HAV Symptoms/jaundice throughout the active course of the disease. Disappearance of HBsAg is thought to be associated with recovery from infec- tion, but some patients continue to have occult HBV infection IgM with detectable HBV DNA and can still transmit virus. High levels of IgM-specific anti-HBc are frequently IgG detected at the onset of clinical illness. Because this antibody is directed against the 27-nm internal core component of HBV, its appearance in the serum is indicative of viral rep- lication. Antibody to HBsAg is first detected at a variable Level of detection period after the disappearance of HBsAg. It is present in low 0 2 4 6 8 10 12 concentrations. Before HBsAg disappears, HBeAg is replaced Weeks after exposure by anti-HBe, signaling the start of resolution of the disease. However, some patients can develop HBeAg negative chronic FIGURE 35-7 Immunologic and biologic events associated with human infection with hepatitis A virus. IgG, immunoglobulin G; hepatitis with pre-core HBV mutants, usually associated with IgM, immunoglobulin M. (Reproduced from Hollinger FB, Ticehurst a stop codon mutation at nucleotide 1896 that results in absent JR: Hepatitis A virus. In Fields BN, Knipe DM, Howley PM [editors- HBeAg production but with continued viral progression. in-chief]. Fields Virology, 3rd ed. Lippincott-Raven, 1996. Modified By definition, HBV chronic carriers are those in whom with permission from Hollinger FB, Dienstag JL: Hepatitis viruses. HBsAg persists for more than 6 months in the presence of In Lennette EH [editor]. Manual of Clinical Microbiology, 4th ed. HBeAg or anti-HBe. HBsAg may persist for years after loss American Society for Microbiology, 1985.) of HBeAg. In contrast to the high titers of IgM-specific anti- HBc observed in acute disease, low titers of IgM anti-HBc are found in the sera of most chronic HBsAg carriers. Small of hepatitis A. Enzyme-linked immunosorbent assay is the amounts of HBV DNA are usually detectable in the serum as method of choice for measuring HAV antibodies. long as HBsAg is present. The most useful detection methods are enzyme-linked B. Hepatitis B immunosorbent assay for HBV antigens and antibodies and Clinical and serologic events after exposure to HBV are PCR for viral DNA. depicted in Figure 35-8 and summarized in Table 35-8. DNA polymerase activity, HBV DNA, and HBeAg, which are rep- C. Hepatitis C resentative of the viremic stage of hepatitis B, occur early in the incubation period, concurrently or shortly after the first Clinical and serologic events associated with HCV infec- tions are shown in Figure 35-9. Most primary infections are asymptomatic or clinically mild (20–30% have jaundice; TABLE 35-7 Interpretation of Hepatitis A, C, and D 10–20% have only nonspecific symptoms such as anorexia, Virus Serologic Markers in Patients with Hepatitis malaise, and abdominal pain). Serologic assays are avail- able for diagnosis of HCV infection. Enzyme immunoas- Assay Results Interpretation says detect antibodies to HCV but do not distinguish among Anti-HAV IgM positive Acute infection with HAV acute, chronic, or resolved infection (see Table 35-7). Anti- HCV antibodies can be detected in 50–70% of patients at Anti-HAV IgG positive Past infection with HAV the onset of symptoms, but in others, antibody appearance Anti-HCV positive Current or past infection with is delayed 3–6 weeks. Antibodies are directed against core, HCV envelope, and NS3 and NS4 proteins and tend to be relatively Anti-HD positive, HBsAg Infection with HDV low in titer. Nucleic acid-based assays (eg, reverse transcrip- positive tion PCR) detect the presence of circulating HCV RNA and Anti-HD positive, anti-HBc IgM Coinfection with HDV and HBV are useful for diagnosis of acute infection soon after exposure positive and for monitoring patients on antiviral therapy. Nucleic acid Anti-HD positive, anti-HBc IgM Superinfection of chronic HBV assays also are used to genotype HCV isolates. negative infection with HDV Anti-HAV, antibody to hepatitis A virus (HAV); anti-HBc, antibody to hepatitis B D. Hepatitis D core antigen; anti-HCV, antibody to hepatitis C virus (HCV); anti-HD, antibody to hepatitis D virus (HDV); HBcAg, hepatitis B core antigen; HBsAg, hepatitis B surface Serologic patterns after HDV infection are shown in antigen; HBV, hepatitis B virus; IgG, immunoglobulin G; IgM, immunoglobulin M. Figure 35-10 and listed in Table 35-7. Because HDV depends Riedel_CH35_p511-p530.indd 519 04/04/19 5:04 PM  520   SECTION IV  Virology Incubation Prodrome, Convalescence period acute disease Early Late Important HBsAg Anti-HBs diagnostic tests IgM anti-HBc IgG anti-HBc 1 2 3 4 5 6 7 8 DNA polymerase HBV particles Relative Anti-HBc concentration of reactants HBsAg Anti-HBs HBeAg Level of Anti-HBe detection Months after exposure 1 2 3 4 5 6 7 8 ALT Symptoms FIGURE 35-8 Clinical and serologic events occurring in a patient with acute hepatitis B virus infection. The common diagnostic tests and their interpretation are presented in Table 35-8. ALT, alanine aminotransferase; anti-HBc, antibody to hepatitis B core antigen; anti-HBe, antibody to hepatitis B e antigen; anti-HBs, antibody to hepatitis B surface antigen; HBeAg, hepatitis B e antigen; HBsAg, hepatitis B surface antigen; HBV, hepatitis B virus; IgG, immunoglobulin G; IgM, immunoglobulin M. (Reproduced with permission from Hollinger FB, Dienstag JL: Hepatitis B and D viruses. In Murray PR [editor]. Manual of Clinical Microbiology, 7th ed. Washington DC: ASM Press, 1999. ©1999 American Society for Microbiology. No further reproduction or distribution is permitted without the prior written permission of American Society for Microbiology.) TABLE 35-8 Interpretation of Hepatitis B Virus Serologic Markers in Patients with Hepatitisa Assay Results HBsAg Anti-HBs Anti-HBc Interpretation Positive Negative Negative Early acute HBV infection. Confirmation is required to exclude nonspecific reactivity. Positive (±) Positive HBV infection, either acute or chronic. Differentiate with IgM anti-HBc. Determine level of replicative activity (infectivity) with HBeAg or HBV DNA. Negative Positive Positive Indicates previous HBV infection and immunity to hepatitis B. Negative Negative Positive Possibilities include HBV infection in remote past; “low-level” HBV carrier; “window” between disappearance of HBsAg and appearance of anti-HBs; or false-positive or nonspecific reaction. Investigate with IgM anti-HBc and HBV DNA. When present, anti-HBe helps validate the anti-HBc reactivity. Negative Negative Negative Never infected with HBV. Possibilities for liver injury include another infectious agent, toxic injury to the liver, disorder of immunity, hereditary disease of the liver, or disease of the biliary tract. Negative Positive Negative Successful vaccine response to HBV immunization. Anti-HBc, antibody to hepatitis B core antigen; anti-HBe, antibody to hepatitis B e antigen; anti-HBs, antibody to hepatitis B surface antigen (HBsAg); HBeAg, hepatitis B e antigen; HBV, hepatitis B virus; IgM, immunoglobulin M. a Modified and reproduced with permission from Hollinger FB: Hepatitis B virus. In Fields BN, Knipe DM, Howley PM (editors-in-chief). Fields Virology, 3rd ed. Lippincott- Raven, 1996. Riedel_CH35_p511-p530.indd 520 04/04/19 5:04 PM  CHAPTER 35 Hepatitis Viruses   521 Events ALT anti-HCV HCV + + + + + + + + RNA SYMPTOMS // Months // Year 0 3 mo 6 mo 9 mo 12 mo 5 yr 10 yr 15 yr 20 yr 25 yr Acute Chronic active HCC hepatitis hepatitis Cirrhosis FIGURE 35-9 Clinical and serologic events associated with hepatitis C virus (HCV) infection. ALT, alanine aminotransferase; anti-HCV, antibody to HCV; HCC, hepatocellular carcinoma. (Reproduced with permission from Garnier L, Inchauspé G, Trépo C: Hepatitis C virus. In Richman DD, Whitley RJ, Hayden FG [editors]. Clinical Virology, 2nd ed. ASM Press, 2002. Washington, DC. ©2002 American Society for Microbiology. No further reproduction or distribution is permitted without the prior written permission of American Society for Microbiology.) HBV-HDV coinfection ALT HBsAg IgM Anti-HBc IgG HDV RNA IgM HDAg Anti-HD IgG Acute HDV, superinfection HBsAg ALT HDV RNA HDAg Chronic HDV, superinfection HBsAg ALT HDV RNA HDAg 0 2 4 6 8 10 12 24 32 Weeks after exposure FIGURE 35-10 Serologic patterns of type D hepatitis after coinfection or superinfection of a person with hepatitis B virus (HBV) infection. Top: Coexistent acute hepatitis B and hepatitis D. Middle: Acute hepatitis D superimposed on a chronic HBV infection. Bottom: Acute hepatitis D progressing to chronic hepatitis, superimposed on a chronic HBV infection. ALT, alanine aminotransferase; anti-HBc, antibody to hepatitis B core antigen; anti-HD, antibody to delta antigen; HBsAg, hepatitis B surface antigen; HDAg, delta antigen; HDV, hepatitis D virus; IgG, immunoglobulin G; IgM, immunoglobulin M. (Reproduced with permission from Purcell RH et al: Hepatitis. In Schmidt NJ, Emmons RW [editors]. Diagnostic Procedures for Viral, Rickettsial and Chlamydial Infections, 6th ed. American Public Health Association, 1989.) Riedel_CH35_p511-p530.indd 521 04/04/19 5:04 PM  522   SECTION IV  Virology on a coexistent HBV infection, acute type D infection occurs (HIV) type 1 disease than other HCV genotypes. In contrast, either as a simultaneous infection (coinfection) with HBV or HCV genotype 2 responds the best to IFN-based therapies. as a superinfection of a person chronically infected with HBV. Genotype 3 shows the highest rate of spontaneous clearance, In the coinfection pattern, antibody to HDAg develops late in and genotype 4 seems to have the highest frequency leading the acute phase of infection and may be of low titer. Assays for to chronic infection after acute infection. HDAg or HDV RNA in the serum or for IgM-specific anti- Less is known about host immune responses to HCV. HDV are preferable. All markers of HDV replication disap- The majority of acute infections are asymptomatic or mild, pear during convalescence; even the HDV antibodies may and chronic infections usually progress slowly and insidi- disappear within months to years. However, superinfection ously. It appears that the immune response is slow to develop by HDV usually results in persistent HDV infection (>70% of and relatively weak, reflecting the fact that HCV has particu- cases). High levels of both IgM and IgG anti-HD persist, as do larly effective immune evasion mechanisms. levels of HDV RNA and HDAg. HDV superinfections may be associated with fulminant hepatitis. Epidemiology Virus–Host Interactions The global distributions of hepatitis A, B, and C infections are Currently, there is evidence for five hepatitis viruses—types shown in Figure 35-11. There are marked differences in the A, B, C, D, and E. A single infection with any is believed to epidemiologic features of these infections (see Table 35-4). confer homologous but not heterologous protection against The risk of these viruses being transmitted by transfu- reinfection. A possible exception may be HCV; reinfection sion today in the United States is markedly reduced as a result with HCV may occur. of improved screening tests, including nucleic acid testing Most cases of hepatitis type A presumably occur with- and the establishment of volunteer donor populations. It was out jaundice during childhood, and by late adulthood there calculated in 2012 that the risk of transmission of HBV by is a widespread resistance to reinfection. However, serologic blood transfusion was one in 1.7 million and for HCV was studies in the United States and several Asian countries indi- one in 6–7 million donations. cate that the incidence of infection may be declining as a result of improvements in sanitation commensurate with a A. Hepatitis A rise in the standard of living coupled with expanded use of HAV is widespread throughout the world. Outbreaks of the vaccine in some countries. It has been estimated that as type A hepatitis are common in families and institutions, many as 60–90% of young middle- to upper-income adults in summer camps, day care centers, neonatal intensive care the United States may be susceptible to type A hepatitis. units, and among military troops. The most likely mode Infection with HBV of a specific subtype (eg, HBsAg/adw) of transmission under these conditions is by the fecal–oral appears to confer immunity to other HBsAg subtypes, prob- route through close personal contact. Stool specimens may ably because of their common group a specificity. The immu- be infectious for up to 2 weeks before to 2 weeks after onset nopathogenetic mechanisms that result in viral persistence of jaundice. and hepatocellular injury in type B hepatitis remain to be Under crowded conditions and poor sanitation, HAV elucidated. As the virus is not cytopathic, it is believed that infections occur at an early age; most children in such cir- hepatocellular injury during acute disease represents a host cumstances become immune by age 10 years. Clinical ill- immune attack against HBV-infected hepatocytes. ness is uncommon in infants and children; disease is most Host responses, both immunologic and genetic, have often manifest in children and adolescents, with the highest been proposed to account for the frequency of HBV chro- rates in those between 5 and 14 years of age. The ratio of nicity in those infected as infants. About 95% of newborns anicteric to icteric cases in adults is about one to three; in infected at birth become chronic carriers of the virus, often children, it may be as high as 12 to 1. However, fecal excre- for life (see Table 35-6). This risk decreases steadily with time tion of HAV antigen and RNA persists longer in the young so that the risk of infected adults becoming carriers decreases than in adults. to 10%. Hepatocellular carcinoma is most likely to occur in Recurrent epidemics are a prominent feature. Sudden, adults who experienced HBV infection at a very early age and explosive epidemics of type A hepatitis usually result from became carriers. Therefore, for vaccination to be maximally fecal contamination of a single source (eg, drinking water, effective against the carrier state, cirrhosis, and hepatoma, it food, or milk). The consumption of raw oysters or improperly must be carried out during the first week of life. steamed clams obtained from water polluted with sewage has HCV genotypes 1–4 are the predominant types circulat- also resulted in several outbreaks of hepatitis A. The largest ing in Western countries and display some differential char- outbreak of this type occurred in Shanghai in 1988, when acteristics. Genotype 1 is predominant in North America, more than 300,000 cases of hepatitis A were attributed to Japan, and Western Europe. It shows the poorest response uncooked clams from polluted water. A multistate foodborne to interferon (IFN) therapy and may have a more deleterious outbreak that was traced to frozen strawberries occurred in effect on the progression of human immunodeficiency virus the United States in 1997. Riedel_CH35_p511-p530.indd 522 04/04/19 5:04 PM  CHAPTER 35 Hepatitis Viruses   523 Other identified sources of potential infection are non- Transfusion-associated hepatitis A is rare because the viremic human primates. There have been more than 35 outbreaks in stage of infection occurs during the prodromal phase and is of which primates, usually chimpanzees, have infected humans short duration, the titer of virus in the blood is low, and there in close personal contact with them. is no carrier state. However, a 1996 report documented the HAV is seldom transmitted by the use of contaminated transmission of HAV to individuals with hemophilia through needles and syringes or through the administration of blood. clotting factor concentrates. There is little evidence for HAV A Countries/areas with moderate to high risk of infection Source: WHO, 2011 B Countries/areas with moderate to high risk of infection Source: WHO, 2011 FIGURE 35-11 Global distribution of hepatitis viruses causing human disease. A: Hepatitis A virus. B: Hepatitis B virus. (Source: World Health Organization, 2011.) Riedel_CH35_p511-p530.indd 523 04/04/19 5:04 PM  524   SECTION IV  Virology Prevalence of infection >10% 2.5–10% Source: WHO, 2001 C 1–2.5% FIGURE 35-11 (Contineud) C: Hepatitis C virus. (Source: World Health Organization, 2001.)   transmission by exposure to urine or nasopharyngeal secre- The major modes of HBV transmission during infancy tions of infected patients. Hemodialysis plays no role in the are from an infected mother to her newborn during delivery spread of hepatitis A infections to either patients or staff. and from an infected household contact to an infant. In the United States in the prevaccine era, there were There is no seasonal trend for HBV infection and no an estimated 271,000 infections per year. Since the advent of high predilection for any age group, although there are hepatitis A vaccines, infection rates have declined sharply to definite high-risk groups, such as parenteral drug abusers, an estimated 2700 cases in 2011. institutionalized persons, health care personnel, multiply Groups that are at increased risk of acquiring hepatitis A transfused patients, organ transplant patients, hemodialysis are travelers to developing countries from developed countries, patients and staff, highly promiscuous persons, and newborn men who have sex with men, users of injection and noninjec- infants born to mothers with hepatitis B. Mandatory screen- tion drugs, persons with clotting factor disorders, and persons ing of blood donors for markers of HBV infection (HBsAg, working with nonhuman primates. Individuals with chronic HBc Ab, and HBV DNA) has substantially reduced the num- liver disease are at increased risk for fulminant hepatitis if a hep- ber of cases of transfusion-associated hepatitis. People have atitis A infection occurs. These groups should be vaccinated. been infected by improperly sterilized syringes, needles, or scalpels and even by tattooing or ear piercing. B. Hepatitis B Other modes of transmission of hepatitis B exist. HBsAg can HBV is worldwide in distribution. Transmission modes and be detected in saliva, nasopharyngeal washings, semen, men- response to infection vary, depending on the age at time of strual fluid, and vaginal secretions as well as in blood. Transmis- infection (Table 35-6). Most individuals infected as infants sion from carriers to close contacts by the oral route or by sexual develop chronic infections. As adults, they are subject to liver or other intimate exposure occurs. There is strong evidence of disease and are at high risk of developing hepatocellular car- transmission from persons with subclinical cases and carriers cinoma. There are more than 350 million carriers, of whom of HBsAg to homosexual and heterosexual long-term partners. about 1 million live in the United States; 25% of carriers Transmission by the fecal–oral route has not been documented. develop chronic active hepatitis. Worldwide, about 600,000 Recalling that there may be more than 1 billion virions/mL of deaths a year are attributed to HBV-related liver disease and blood from an HBeAg positive carrier and that the virus is resis- hepatocellular carcinoma. tant to drying, it should be assumed that all bodily fluids from There is a high burden of HBV infections among HBV-infected patients may be infectious. Subclinical infections HIV-infected persons, with 36% prevalence in 2008 in the are common, and these unrecognized infections represent the United States. principal hazard to hospital personnel. Riedel_CH35_p511-p530.indd 524 04/04/19 5:04 PM  CHAPTER 35 Hepatitis Viruses   525 Health care personnel (medical and dental surgeons, transmitted to an organ transplant recipient from an HCV- pathologists, other physicians, nurses, laboratory technicians, positive donor. and blood bank personnel) have a higher incidence of hepatitis The average incubation period for HCV is 6–7 weeks. The and prevalence of detectable HBsAg or anti-HBs than those who average time from exposure to seroconversion is 8–9 weeks, have no occupational exposure to patients or blood products. and about 90% of patients are anti-HCV positive within The risk that these apparently healthy HBsAg carriers (espe- 5 months. cially medical and dental surgeons) represent to the patients under their care remains to be determined but is probably small. D. Hepatitis D (Delta Agent) Hepatitis B infections are common among patients and HDV is found throughout the world but with a nonuniform staff of hemodialysis units. As many as 50% of the renal dial- distribution. Its highest prevalence has been reported in Italy, ysis patients who contract hepatitis B may become chronic the Middle East, central Asia, West Africa, and South America. carriers of HBsAg compared with 2% of the staff group, HDV infects all age groups. Persons who have received mul- emphasizing differences in the host immune response. Fam- tiple transfusions, intravenous drug abusers, and their close ily contacts are also at increased risk. contacts are at high risk. The incubation period of hepatitis B is 50–180 days, with The primary routes of transmission are believed to be a mean between 60 and 90 days. It appears to vary with the similar to those of HBV, although HDV does not appear to be dose of HBV administered and the route of administration, a sexually transmitted disease. Infection depends on HBV rep- being prolonged in patients who receive a