Acute and Chronic Infectious Hepatitis

Clinical Features

Acute viral hepatitis is often asymptomatic, and in many patients, it is recognized only in retrospect after serological tests reveal evidence of prior infection. In symptomatic patients, presenting symptoms often are only mild and nonspecific and include malaise, fatigue, low-grade fever, and flulike complaints. Asymptomatic or mild acute viral hepatitis is more common in children; adults are more likely to be symptomatic.

Symptomatic acute viral hepatitis is usually preceded by a prodrome phase that lasts from a few days to several weeks and is characterized by nonspecific symptoms such as nausea, vomiting, myalgia, anorexia, and malaise. Once jaundice develops, constitutional symptoms typically begin to wane. Physical examination is often notable only for jaundice and hepatomegaly. In addition, the liver may be tender to palpation. Serum aminotransferases, which are the key indicators of hepatocellular injury, are commonly elevated 10-fold above normal and often exceed 1000 units/L. In contrast, alkaline phosphatase is typically only mildly elevated; conjugated hyperbilirubinemia is present in some, but not all, patients. In most cases, full recovery occurs within a few weeks. In some, low-grade symptoms or signs persist for months. The treatment of acute viral hepatitis is generally supportive.

Fulminant hepatic failure develops in <1% of acute viral hepatitis cases. This is characterized by the rapid development of liver decompensation. Although acute liver failure may result from a variety of other causes, including exposure to drugs or toxins, autoimmune liver disease, or ischemia, 12% of cases in the United States are caused by acute viral hepatitis. The clinical course of acute hepatic failure is characterized by coagulopathy, encephalopathy, and a high mortality rate in patients who do not undergo liver transplantation. For both acute HAV and acute HEV infection, patients with a background of chronic liver disease have a higher risk of a poor outcome.

Pathological Features

Table 47.1 summarizes the pathological features of acute and chronic hepatitis.

Patients with acute viral hepatitis seldom undergo liver biopsy because the diagnosis is usually easily established by noninvasive serological tests. On low-power microscopic examination, acute cases show a necroinflammatory process that involves all areas of the hepatic lobules, and hence it is not confined to the portal tracts. The combination of hepatocyte injury, loss, and regeneration with the presence of a mononuclear inflammatory infiltrate leads to a pattern termed lobular disarray , which reflects a disruption of the normal orderly architecture of the liver cell plates ( Fig. 47.1 ).

Lobular hepatocellular changes include hepatocyte swelling, in which the affected cells are pale stained and show irregular, wispy cytoplasm and clumping of cytoplasm around the nucleus. Other forms of hepatocyte necrosis occur as well (described later). Swollen hepatocytes often undergo “lytic necrosis,” marked by the presence of small foci of stromal collapse associated with small clusters of mononuclear inflammatory cells. In addition, hepatocytes may undergo acidophilic changes, in which the cell becomes shrunken, angular, and hypereosinophilic and contains a densely stained pyknotic nucleus. This type of necrosis leads to acidophil bodies (apoptotic bodies), which are small, mummified, rounded cell remnants that may also extrude fragments of degenerated nuclei. Apoptotic bodies may be phagocytosed by Kupffer cells, resulting in Kupffer cell hyperplasia. Individual or small clusters of necrotic hepatocytes are collectively referred to as “spotty” hepatocyte necrosis. Regeneration of hepatocytes contributes to the “busy” appearance of the hepatic lobules, because the liver cell plates are typically irregular and thickened. Nonspecific steatosis may also occur in cases of acute hepatitis.

Canalicular cholestasis is not normally a prominent feature in cases of acute viral hepatitis. However, cholestasis may occasionally be so prominent that the histological changes mimic those of biliary obstruction. In this variant, termed acute cholestatic hepatitis , one sees marked lobular inflammation and hepatocanalicular cholestasis. There may also be bile accumulation within the lumina of bile ducts and ductules. The finding of a prominent bile ductular reaction associated with neutrophils (termed cholangiolitis ) in the portal tracts may contribute to confusion with biliary obstruction. Marked hepatocyte swelling and regenerating cholestatic rosettes (hepatocyte “pseudoglands”) may be present in the hepatic lobules ( Figs. 47.2 and 47.3 ). Typically, cases of acute cholestatic hepatitis have a more prolonged clinical course.

The inflammatory infiltrate in cases of acute viral hepatitis is primarily mononuclear. It is composed of lymphocytes, macrophages, scattered eosinophils, and occasional plasma cells and neutrophils ( Fig. 47.4 ). In contrast to chronic viral hepatitis, in which portal and periportal inflammation typically predominates, the inflammatory infiltrate in acute viral hepatitis usually is not concentrated to the portal tracts but is spread more evenly throughout the hepatic lobules. Sinusoidal mononuclear cells are often prominent. Kupffer cells are often more prominent and more numerous than usual; they are hypertrophic and may contain phagocytized cellular debris and abundant lipofuscin pigment, which is highlighted by staining with periodic acid–Schiff (PAS) stain after diastase digestion ( Figs. 47.5 and 47.6 ).

Although the necroinflammatory process is typically panlobular, inflammation and necrosis in acute hepatitis may be more pronounced in the centrilobular areas. Bridging necrosis may develop in severe cases. This feature appears as a zone of necrosis that extends from the portal tracts to the central veins, and it is often associated with a more protracted clinical course ( Fig. 47.7 ).

Immunohistochemistry for detection of viral antigens is generally not considered useful for evaluation of acute viral hepatitis because the virus is rapidly eliminated from liver cells and therefore is not detectable. Serological tests are the most reliable, and readily available, for diagnostic purposes.

Massive and Submassive Necrosis

In severe cases of acute viral hepatitis, large portions of the hepatocyte lobules (submassive necrosis) or entire contiguous lobules (massive necrosis) may undergo necrosis. Submassive necrosis usually involves zone 3 hepatocytes initially, but it may extend to zone 2 regions with progression. Extensive destruction of hepatic parenchyma results in the clinical syndrome of “fulminant hepatic failure.” On gross examination, livers with massive necrosis appear shrunken and flaccid, often showing wrinkling of the capsular surface and a mottled appearance of the liver parenchyma. Regenerating nodules of hepatocytes, which are often bile stained, may be irregularly distributed in the liver and may form nodular masses. The degree of necroinflammatory activity is variable, even among patients with a similar clinical course. In fulminant cases, one often sees a prominent bile ductular reaction, with associated neutrophils (cholangiolitis), which is typically located in the peripheral region of the portal tracts ( Fig. 47.8 ). However, the histological features of submassive or massive hepatic necrosis are not specific for acute viral hepatitis. This pattern of injury can develop as a result of toxic injury, severe drug reaction, or Wilson’s disease, among other causes. A trichrome stain to highlight connective tissue is useful to distinguish massive hepatic necrosis from cirrhosis, by demonstrating the lack of dense collagen deposition in the former. A reticulin stain is also helpful to demonstrate the presence of a collapsed reticulin framework ( Fig. 47.9 ).

Prognostic Factors

Pathological features of acute viral hepatitis that are predictive of progression to chronicity are difficult to elucidate, in part because of the rarity of liver biopsies from patients with acute hepatitis. Furthermore, in patients with massive hepatic necrosis, an individual liver biopsy may not represent the overall status of the liver, because hepatocyte regeneration and necrosis can vary substantially from region to region.

Differential Diagnosis

Several major entities may be confused with acute viral hepatitis—in particular, chronic viral hepatitis, autoimmune hepatitis, and drug-induced hepatitis ( Table 47.2 ). In cases in which the lobular inflammatory component is prominent, a markedly active chronic hepatitis may be confused with acute hepatitis. Some patients with autoimmune hepatitis exhibit an “acute” clinical picture and have a prominent lobular inflammatory infiltrate with extensive necrosis that may be difficult to distinguish from acute viral hepatitis. However, autoimmune hepatitis often reveals prominent plasma cell infiltrates. Even in the acute presentation of autoimmune hepatitis, plasma cell infiltration can be seen in the portal tracts and is associated with interface activity, albeit centrilobular necrosis and lobular plasma cell infiltration can be seen in this acute presentation as well. In addition, fibrosis often exists at the time of the initial biopsy in patients with autoimmune hepatitis, even with an acute clinical picture. Of note, the Masson’s trichrome stain used routinely to evaluate for fibrosis in livers must be evaluated with caution in fulminant hepatitis. Parenchymal collapse or areas of necrosis may mimic fibrosis but will have a paler blue color in comparison to the darker blue of true established fibrosis in chronic hepatitis ( Fig. 47.10 ). To assist in this distinction, the trichrome staining pattern in suspected parenchymal collapse should be compared with the darker blue of the collagen surrounding portal structures. Reticulin stains can also help highlight areas of collapse and parenchymal extinction. Serological tests for autoimmune markers are usually helpful, although recent literature has shown that up to 20% of patients with clinical and histological features of autoimmune hepatitis have negative autoimmune serologies, particularly early in the course of disease. Viral serologies and molecular testing for DNA or RNA are of course helpful in confirming or excluding viral hepatitis.

Drug-induced hepatitis can be indistinguishable from acute viral hepatitis (see Chapter 48 for more detail). The presence of prominent eosinophils, granulomas, sinusoidal dilation, prominent bile ductular reaction, cholestasis, and fatty change may suggest a drug reaction, but these are not considered pathognomonic features. Pericentral hepatocyte necrosis and dropout, as seen in classical Tylenol overdose, or overlapping findings of both cholestasis and lobular hepatitis suggest a drug reaction. Acute or chronic hepatitis that does not seem to fit into a discrete morphological category should raise the possibility of a drug reaction as well. Obtaining a complete history of drug and toxin exposures is critical to distinguish drug reactions from viral hepatitis. Furthermore, superimposed drug injury may develop in patients with acute viral hepatitis, so the two entities are not necessarily mutually exclusive.

A common clinical scenario that pathologists may encounter is a biopsy specimen obtained weeks after the appearance of clinical symptoms and elevated liver enzymes indicative of acute hepatitis. In this situation, a nearly normal liver with aggregates of Kupffer cells in areas of hepatocyte dropout may be the only finding. A PAS-D stain can highlight the debris-filled macrophages, suggesting a resolving phase of hepatic injury. Importantly, Kupffer cell aggregates should not be mistaken for nonnecrotizing granulomas.

Clinical Features

As in acute hepatitis, patients with chronic hepatitis have a wide spectrum of clinical manifestations that range from asymptomatic to symptomatic and decompensated cirrhosis. Many patients are asymptomatic or have only mild, nonspecific complaints, such as fatigue. Findings on physical examination are typically few but include hepatomegaly and other stigmata of chronic liver disease, such as palmar erythema. Ascites and esophageal or cutaneous varices may also develop in patients with advanced cirrhosis. Serum aminotransferase levels fluctuate but are usually chronically elevated in the 2- to 10-fold range, although a substantial number of patients with mild chronic hepatitis C have persistently normal aminotransferase levels. Alkaline phosphatase and bilirubin levels are usually normal to only mildly elevated, unless hepatic decompensation has occurred, in which case high levels may be observed.

Pathological Features

As mentioned previously, chronic hepatitis is defined clinically as persistent necroinflammatory liver disease. Regardless of the specific etiology, chronic hepatitis is characterized by a combination of portal inflammation, interface (periportal) hepatitis, varying degrees of parenchymal inflammation and necrosis, and, in many cases, fibrosis. This histological pattern of injury is not specific for chronic viral hepatitis. It may also be seen in many other chronic conditions, such as autoimmune hepatitis, metabolic disorders such as Wilson’s disease and α ₁ -antitrypsin deficiency, chronic biliary disorders also exhibiting portal inflammation and fibrosis, and various types of drug reactions. Table 47.3 summarizes the histopathological features of chronic hepatitis (see also Table 47.1 ).

Portal Inflammation

Chronic hepatitis is characterized by the presence of an inflammatory infiltrate that involves the portal tracts, which may range from mild and patchy to prominent and diffuse. The infiltrates consist primarily of lymphocytes, often associated with a variable number of plasma cells. Scattered macrophages, neutrophils, and eosinophils may be found in some cases, but they are typically a minor component of the infiltrate in chronic viral hepatitis. Lymphoid follicles may be present, particularly in hepatitis C, and germinal centers may also be present ( Fig. 47.11 ). A bile ductular reaction may be seen at the periphery of portal tracts, but this feature is not specific and usually is not very prominent in viral hepatitis. As with any type of bile ductular reaction, neutrophils are usually associated with the proliferating ductular epithelium as a result of cytokines released by biliary epithelium, and this should not be interpreted as evidence of biliary obstruction or acute cholangitis. Mild bile duct injury can also be seen, but this is not a prominent feature of chronic viral hepatitis.

Typically, the majority of portal tracts are equally involved by the inflammatory process. Interface hepatitis, also known as interface activity or piecemeal necrosis , is characterized by inflammation and injury of the adjacent hepatocytes immediately surrounding the portal tracts. It is an important and common feature of chronic viral hepatitis, although it may be focal, or even absent, in cases with minimal or mild necroinflammatory activity. Lymphocytes and plasma cells in the periportal infiltrate are closely associated with degenerating hepatocytes ( Fig. 47.12 ), such that indentation of the cytoplasm of the hepatocytes occurs, and one might even see engulfment of inflammatory cells by hepatocytes. Hepatocytes in areas of interface hepatitis–associated necrosis often appear pale or swollen and show clumping of cytoplasm. Apoptotic bodies (acidophil bodies) may be present as well.

Lobular Necroinflammatory Activity

In chronic viral hepatitis, hepatocyte necrosis is usually variable in severity and spotty in distribution. Lobular disarray, a feature characteristic of acute hepatitis, is not often prominent in chronic hepatitis unless there is marked activity. Acidophil bodies, which are usually more numerous in the periportal areas, may also be scattered in the hepatic lobules ( Fig. 47.13 ). Mononuclear inflammatory cells tend to cluster around injured or dying hepatocytes ( Fig. 47.14 ). Kupffer cells, in areas of spotty hepatocyte necrosis, may contain phagocytosed cellular debris. Hepatocyte swelling may be present in exacerbations of chronic viral hepatitis and may also be associated with zone 3 cholestasis. Regeneration of hepatocytes is recognized by the formation of liver cell plates that are two cells thick and by the formation of regenerating hepatocyte rosettes, as well as mitotically active hepatocytes.

Fibrosis

Progressive fibrosis of the limiting plate, as a result of continued necroinflammatory activity, leads to enlargement of the portal tracts and stellate periportal fibrous extensions ( Fig. 47.15 ). Deposition of collagen and other extracellular matrix materials in the space of Disse at the leading edge of periportal fibrosis also results in capillarization of the sinusoids. Portal-portal fibrous septa represent the fibrous linkage of adjacent fibrotic portal tracts ( Fig. 47.16 ). Portal-central fibrous bridges may also develop from superimposed episodes of severe lobular necroinflammatory activity involving zone 3 of the hepatic lobules. Central-central bridges form by the same mechanism but are far less common in chronic viral hepatitis. The end result of bridging fibrosis is cirrhosis, which is usually macronodular or of a mixed micronodular and macronodular type.

Nomenclature and Scoring

In the past, the term chronic active hepatitis was used to describe liver biopsies with interface hepatitis, and the term chronic persistent hepatitis was used for biopsies with portal inflammation but without significant periportal/piecemeal necrosis. This distinction was thought to be clinically important, because chronic persistent hepatitis was considered a relatively benign process without a high risk of progression to significant chronic liver disease. However, on identification of hepatitis C, and on recognition of the waxing and waning nature of the disease and the prolonged time to progression to cirrhosis in many cases, this nomenclature has been abandoned. Currently, the recommended practice is to use the term chronic hepatitis and include a statement in the pathology report regarding the severity of necroinflammatory activity (grade), extent of fibrosis (stage), and etiology. Prognostic factors should also be noted in the report (see later discussion).

Several different systems for scoring necroinflammatory activity and fibrosis have been developed ( Table 47.4 ). The original Knodell system, first published in 1981, served as the prototype semiquantitative liver inflammation and fibrosis scoring system. With modifications—such as the one proposed by Ishak and coworkers, which separates the grade of inflammation and necrosis from fibrosis—this system is still widely used, particularly in therapeutic trials in which the necroinflammatory activity in pretreatment and posttreatment liver biopsy specimens are compared. ^, In the original Knodell system, periportal necrosis (with or without bridging necrosis, intralobular necrosis, and inflammation), portal inflammation, and fibrosis are all assigned numeric values, which are then added to obtain a hepatitis activity index (HAI) that ranges from 0 to 22. One major criticism of this system is the inclusion of fibrosis (stage) as a determinant of activity (grade). In practice, the HAI is often modified so that bridging necrosis is dissociated from interface hepatitis, and only the elements that relate to grade are added together to produce the modified HAI (mHAI), with scores that range from 0 to 18; the stage, which indicates degree of fibrosis, is reported separately (see Table 47.4 ). An alternative grading system used by the French METAVIR Cooperative Study Group evaluates only two features (periportal necrosis and lobular necroinflammatory activity) instead of three; portal inflammation is excluded because it is considered a prerequisite for the diagnosis of chronic hepatitis, even in cases without parenchymal activity.

The various semiquantitative grading schemes, although useful for evaluating the effects of a particular treatment regimen in clinical trials, are typically not necessary or clinically relevant for routine pathology reporting of liver biopsies. For everyday diagnostic purposes, simpler schemes are sufficient. For instance, the Batts-Ludwig scoring system ( Table 47.5 ) uses 5 categories (0 through 4) separately for both grade and stage ( Figs. 47.17 and 47.18 ). In the Batts-Ludwig system, grade is determined by evaluation of the degree of interface activity (lymphocytic piecemeal necrosis), lobular inflammation, and necrosis. Stage is scored from 0 to 4. A zero score refers to normal connective tissue (no fibrosis). Stage 1 indicates fibrous expansion of portal tracts; stage 2, periportal fibrosis; stage 3, portal-portal bridging fibrous septa; and stage 4, cirrhosis (see Fig. 47.18 ). Pathological stage is best evaluated with the use of a Masson trichrome stain, because delicate periportal or early bridging fibrous septa may not be easily apparent on hematoxylin and eosin (H&E) stain.

Prognostic Factors

Factors associated with progression of chronic viral hepatitis to cirrhosis may be divided into those related to specific viruses, host-related factors (see Treatment of Chronic Hepatitis C), and extraneous factors (e.g., alcohol use). For hepatitis C, development of chronic hepatitis is not related to the amount of virus at initial exposure. Viral genotype may be important in the progression of HCV infection. For instance, genotype 1 is associated with more severe disease than genotype 2. ^, However, other studies have not confirmed this association. Host-related factors for disease severity are incompletely defined, but age at infection and gender appear to be relevant. Males and older individuals are more likely to show progression of fibrosis. ^, Alcohol consumption increases replication of hepatitis C and is associated with more severe disease. In general, the grade of hepatic necroinflammatory activity in liver biopsy specimens correlates with the serum HCV RNA level, and the rate of progression to cirrhosis correlates with high-grade activity and advanced stage in initial liver biopsies. Hepatic steatosis is also associated with increased disease severity and is more commonly seen in infections with genotype 3b, as previously discussed. ^, Accumulation of iron in hepatocytes and Kupffer cells in hepatitis C may influence the disease course and response to therapy adversely. ^, However, many patients with chronic viral hepatitis, including hepatitis C, have abnormal results on serum iron studies but normal or only scant iron accumulation within the liver tissue.

Differential Diagnosis

The morphological patterns of chronic viral hepatitis are not specific to viral infection (see Table 47.4 ). The initial distinction should include distinguishing acute from chronic viral hepatitis, followed by differentiating chronic viral hepatitis from other forms of chronic hepatitis, such as autoimmune hepatitis. Distinction from acute hepatitis rests primarily on the pattern of lobular inflammation and necrosis in acute hepatitis, whereas chronic hepatitis shows predominantly portal inflammatory changes; fibrosis, in particular, is a cardinal sign of disease chronicity. However, in some cases, identification of acute versus chronic hepatitis may not be possible on morphological grounds alone; clinical evidence of chronic disease is usually very helpful.

Other conditions that may resemble chronic viral hepatitis can include primary sclerosing cholangitis (PSC), primary biliary cholangitis (PBC), metabolic disorders, and drug reactions.

PBC is a particularly important mimic of chronic viral hepatitis, because early in the course of disease, portal lymphocytic infiltrates in patients with PBC may resemble chronic viral hepatitis, particularly hepatitis C. The patchy nature of the portal inflammation in PBC, presence of florid-duct lesions, and loss of interlobular bile ducts are helpful distinguishing features because these lesions occur in PBC but not in chronic viral hepatitis. Bile ducts may be infiltrated mildly by lymphocytes in chronic hepatitis C, but the degree of inflammation and duct destruction is not nearly as severe as in PBC. Furthermore, portal granulomas, especially those associated with injured bile ducts, are not a feature of viral hepatitis. In addition, chronic cholestasis is not a feature of precirrhotic chronic viral hepatitis and, by definition, indicates a chronic cholestatic condition. Furthermore, demonstration of increased copper or copper-binding protein by copper stains is helpful in confirming a chronic biliary disorder. Of course, knowledge of the status of viral serological studies and other titers, such as the antimitochondrial antibody level, are most helpful in this differential diagnosis.

The morphological features of PSC, in its early stages, may also overlap with those of chronic viral hepatitis. Both may show a marked portal lymphocytic infiltrate with interface hepatitis; however, this distinction may be particularly difficult in cases of childhood PSC. Once again, bile duct loss suggests a chronic biliary process; alkaline phosphatase levels are typically higher in PSC, but cholangiography is usually necessary to establish a final diagnosis of PSC. The classic “onion-skinning” periductal concentric sclerosing lesions of PSC are not seen in viral hepatitis. In patients with ulcerative colitis and a liver biopsy that shows a pattern of inflammation suggestive of chronic hepatitis, the possibility of PSC should always be strongly considered.

Chronic viral hepatitis may be histologically indistinguishable from autoimmune hepatitis. The presence of numerous plasma cells in the portal inflammatory infiltrate and plasma cells in the lobules is suggestive of autoimmune hepatitis, but an autoimmune-like pattern of hepatitis C has also been described, and clinical correlation is often necessary to reliably distinguish these entities. Even in true cases of autoimmune hepatitis–like hepatitis C, treatment of the HCV addresses the overlap-like condition without the need for immunosuppression, which could exacerbate the infection. Bile duct infiltration by lymphocytes is also seen in autoimmune hepatitis, and therefore, it cannot be used to distinguish this condition from hepatitis C. Once again, serological studies are usually helpful and often diagnostic.

Wilson’s disease may also reveal a chronic hepatitis pattern of injury on liver biopsy, and it should always be considered as a possibility in biopsies from young patients with negative viral serology results. Low serum ceruloplasmin is suggestive, but quantitative copper studies on liver tissue are, ultimately, necessary for a definitive diagnosis. α ₁ -Antitrypsin deficiency may also reveal a pattern of injury resembling chronic hepatitis; accumulation of PAS-positive, diastase-resistant cytoplasmic globules in periportal hepatocytes helps identify this disorder, particularly in liver biopsies from adults.

The spectrum of drug-induced injury in the liver is vast (see Chapter 48 ). Many types of drugs cause a chronic hepatitis morphological pattern of injury that can be difficult to distinguish from other causes, including viral or autoimmune hepatitis. Drugs that commonly cause chronic hepatitis include methyldopa, isoniazid, nitrofurantoin, dantrolene, and sulfonamides. As mentioned earlier, patterns of liver injury that show mixed hepatitic and cholestatic features, prominent eosinophils, cholestasis, or simply do not seem to fit in any discrete etiological category, should always raise consideration of a drug reaction.

Mild lobular hepatitis with spotty hepatocyte necrosis and a scant mononuclear inflammatory infiltrate may be seen as a nonspecific finding in a variety of systemic and immune-mediated disorders, as well as in patients with an intraabdominal inflammatory process. These changes may mimic mild acute or chronic hepatitis but are considered reactive in nature. In some cases, morphological changes of chronic hepatitis in a liver biopsy specimen are not associated with a specific etiology after extensive serological and clinical testing, and these cases may be labeled “cryptogenic” or “idiopathic.” However, a drug reaction should always be considered in this setting. See Chapter 48, Chapter 49 for more details on the differential diagnosis of hepatitis.

Hepatitis A

HAV is a small, 27-nm, nonenveloped, single-stranded RNA virus in the picornavirus family ( Table 47.6 ). Although HAV remains the most common cause of acute viral hepatitis in the world, infection rates in the United States and other countries have declined progressively with increased use of hepatitis A vaccination. Infection rates are higher in areas of poor sanitation or overcrowding, such as in developing countries and in institutions for people with developmental disabilities. Outbreaks in day care centers and residential institutions also occur, although proper handwashing and sewage disposal help reduce spread of the virus.

The major route of transmission of HAV is oral ingestion of fecally excreted virus through person-to-person contact or ingestion of contaminated food or water. Approximately 50% of patients have no identifiable source of infection. Recent outbreaks in the United States have included illicit drug use and direct person-to-person spread as causes. During infection, the virus is transported across intestinal epithelium and travels to the liver through the portal system, where it is taken up by hepatocytes. The virus replicates in hepatocytes and is then excreted into bile and shed into stool. HAV is not directly cytopathic; hepatocyte injury occurs via a cell-mediated immune mechanism. The virus is resistant to bile lysis and can be excreted into the intestine and feces or released into the systemic circulation. There are four genotypes, but only one serotype of the hepatitis A virus. The mean incubation period for HAV is 28 days (range, 15 to 40 days). The diagnosis is usually established by detection of immunoglobulin M (IgM) antibodies to HAV, which are usually detectable in serum within 1 to 2 weeks after exposure and may persist for 3 to 6 months. However, serologies should be interpreted with caution. Antibodies to HAV may not always be indicative of clinical acute hepatitis, and in fact, a positive HAV antibody result is actually associated with a true clinical diagnosis of acute HAV in only a minority of cases. It is important to note that positive HAV-IgM may reflect a dormant infection or reflect a spurious result due to cross-reacting antibodies to another virus. Therefore a positive result may not be completely useful in the absence of symptoms, or outside the context of recognized outbreaks. Anti-IgG antibody to HAV is detectable 5 to 6 weeks after exposure and persists for decades.

The clinical symptoms of HAV infection are usually mild, and many patients are completely asymptomatic. The most important factor that determines severity of disease is patient age: only 30% of children are symptomatic, compared with 70% of adults. The overall case-fatality rate resulting from fulminant hepatitis A is low (0.2%), but HAV infection may produce substantial morbidity in elderly patients and in those with preexisting chronic liver disease. Hepatitis A accounts for 3% of fulminant liver failure overall in the United States. The onset of classic HAV infection is typically abrupt, characterized by the presence of fever, headache, malaise, and nonspecific gastrointestinal (GI) symptoms, followed by jaundice a week later. Symptoms usually resolve within 8 weeks. A relapsing variant of hepatitis A has been recognized, and in as many as 10% of patients, the disease has a prolonged cholestatic course. However, chronic disease as a result of HAV virus infection is extremely rare. Acute hepatitis A is not commonly biopsied. Although histological features of acute HAV resemble those of acute hepatitis in general, plasma cells can be particularly prominent and portal inflammation can also be notable, making it challenging to distinguish from autoimmune hepatitis. Pericentral cholestasis can also be present and it can resemble a biliary obstructive process. Table 47.7 summarizes the clinical, laboratory, and histological features of hepatitis A as well as hepatitis B, C, D, and E.

Hepatitis B

HBV contains a partially double-stranded, circular DNA genome and is a member of the hepadnavirus family of viruses. The complete viral particle, referred to as the Dane particle , consists of an outer envelope that surrounds a core of DNA, the hepatitis B core antigen (HBcAg), the hepatitis B e antigen (HBeAg), and DNA-dependent polymerase. The outer envelope contains the hepatitis B surface antigen (HBsAg). Both complete and incomplete viral particles circulate in the blood of infected patients. In fact, HBsAg can circulate in large quantities as incomplete tubular or spherical structures that lack DNA. Viral DNA may become incorporated into host DNA within infected hepatocytes, particularly in young patients, and these patients are at high risk for subsequent development of hepatocellular carcinoma. The viral antigen load and subsequent antibody response may be used as serological markers to evaluate the time course of infection ( Table 47.8 ).

HBV is transmitted through exposure to infected body fluids and by intravenous drug use, sexual contact, and occupational activity. Perinatal transmission is common (90%) if the mother is HBeAg positive, which is indicative of highly infectious disease and active viral replication, but less common (10%) if the mother is HBsAg positive. In high-prevalence areas, HBV infection is often acquired by maternal–neonatal transmission, which results in a high rate of chronic disease. In areas of low prevalence, hepatitis B is mainly a disease of young adults, who acquire the virus through parenteral or sexual exposure. Posttransfusion hepatitis B is virtually nonexistent in the United States because of routine screening of blood donors.

HBV is responsible for as many as 40% of cases of acute hepatitis in the United States. Clinical symptoms of acute hepatitis develop in approximately 30% of infected adults but in only 10% of children younger than 4 years of age; they typically appear 45 to 180 days after exposure. Fulminant hepatic failure occurs in approximately 1% of cases of acute hepatitis B; however, hepatitis B accounts for 7% of acute liver failure cases in the United States and up to 40% in Japan. Acute liver failure may also occur in patients with chronic hepatitis B in which mutations are present in the precore, or core promoter, regions of the viral DNA. Chronic hepatitis develops in fewer than 10% of adult patients, but in as many as 90% of infected infants. The rate of progression to cirrhosis depends on the presence or absence of active viral replication and the severity of liver damage (evident histologically). For instance, 50% of patients with chronic hepatitis B and marked activity progress to cirrhosis within 4 years. The annual probability that cirrhosis will develop is estimated to be 12% for patients with chronic hepatitis B. Hepatocellular carcinoma develops in 2.4% of patients with chronic hepatitis B annually, as well as in 0.5% of patients with chronic hepatitis without cirrhosis.

Chronic Hepatitis B

Hepatitis B virus infection is characterized by the presence of varying degrees of portal inflammation, interface activity, spotty lobular inflammation, and necrosis. Patients with bridging or confluent necrosis are likely to have more advanced degrees of fibrosis (higher-stage disease). Ground-glass cells containing abundant HBsAg within smooth endoplasmic reticulum may be recognized on H&E-stained tissue sections ( Fig. 47.19 ). However, they are not present in all cases, and they are more likely to be numerous in biopsy samples that contain little necroinflammatory activity. When present, they denote active viral replication. Mimics or “pseudo-ground-glass” hepatocytes have been described in the absence of HBV infection. HBcAg accumulation within hepatocyte nuclei produces a “sanded” appearance, but these changes are also seen in HDV infection and are difficult to recognize on routine histological stains. Identification of cytoplasmic HBsAg may be facilitated by use of one of the Shikata stains, such as Victoria blue, orcein, or aldehyde fuchsin, or by immunohistochemistry ( Fig. 47.20 ). HBcAg accumulation may also be identified with the use of immunohistochemical stains ( Fig. 47.21 ). Cytoplasmic or membranous expression of this antigen correlates with higher levels of necroinflammatory activity. Several phases with histological correlates are worth mentioning: in the “high replicative, low inflammatory” phase (previously known as “immune tolerant”) that can be encountered in HBV chronic infections acquired at birth, the patient characteristically has high serum viral DNA and HBeAg+ status, normal or low serum ALT, and minimal or mild necroinflammatory findings on histology, but have immunohistochemical antigen positivity. These have no or only slow progression of fibrosis ( Fig. 47.22 ). The “immune clearance” phase patient is characterized by oscillating levels of serum HBV DNA and alanine transaminase (ALT) levels that ultimately decrease and the patient loses HBeAg. Liver histology in this phase ranges from high necroinflammation with the episodes of hepatitis and minimal necroinflammation. The HBeAg-negative chronic phase shows moderate/high HBV DNA, high but oscillating ALT, low HGsAg levels, persistent necroinflammation, and progressive liver disease ( Fig. 47.23 ). Rarely, particularly in liver transplant or HIV patients, a rapidly progressive variant called “fibrosing cholestatic hepatitis” can occur; this has striking features of periportal fibrosis, bile ductular reaction, cholestasis, and swollen hepatocytes and may be accompanied by ground-glass change.

Hepatitis C

HCV is a spherical, enveloped, single-stranded RNA virus that measures approximately 50 mm in diameter. It is classified as a separate genus within the Flaviviridae family. The HCV genome is characterized by sequence heterogeneity as a result of pressure from the host immune system. This feature allows the virus to escape immune surveillance and establish chronic infection. Six major genotypes are recognized: the most common are 1a, 1b, 2a, and 2b.

HCV is transmitted primarily by parenteral exposure. Intravenous drug users and patients with hemophilia have a particularly high prevalence rate of infection. Intranasal cocaine use and sexual promiscuity are independent risk factors for infection, although the risk associated with sexual transmission of HCV is low compared with that of the human immunodeficiency virus (HIV) or HBV. Although this virus was initially identified as the etiological agent of transfusion-acquired “non-A, non-B” hepatitis, posttransfusion HCV has decreased dramatically because of widespread implementation of donor screening. The risk of infection with HCV is now estimated to be 0.01% to 0.001% for each unit of blood transfused. Rates of perinatal transmission are estimated to be lower than 5%. Nevertheless, the current opiate crisis continues to make HCV infection a relevant health concern; between 2004 and 2014, there was a 400% increase in acute HCV among 18 to 29 year olds, paralleling the 600% increase in admissions for injected heroin.

HCV accounts for approximately 15% of cases of acute hepatitis in the United States, but acute infection is usually asymptomatic and only rarely recognized clinically. The incidence of acute HCV infection peaked in the late 1980s and early 1990s and has been steadily declining since, to fewer than 20 acute infections per 100,000 individuals per year. The incubation period of hepatitis C is 7 weeks, with a range of 2 to 30 weeks based on studies of transfusion-acquired cases. Fulminant hepatitis C is rare. Chronic infection is a far more common problem, occurring in up to 85% of infected patients. Most patients with chronic hepatitis C have either few, or no, symptoms. Serum aminotransferase levels are often only mildly elevated, fluctuating from 1.5 to 10 times the upper limit of normal, and as many as 30% of patients have normal aminotransferase levels. Factors associated with progressive disease include patient age older than 40 years at the time of exposure, immunodeficiency, a high degree of viral heterogeneity, genotype 1, male gender, and long duration of infection. ^, Alcohol is known to potentiate viral replication and is associated with greater activity and fibrosis. Although hepatic steatosis has been correlated with increased progression of fibrosis, it is unclear whether this result is confounded by associated metabolic abnormalities. Diagnostic tests currently in use include polymerase chain reaction (PCR) for detection of circulating viral RNA and a third-generation enzyme immunoassay for detection of anti-HCV antibodies.

The natural history of HCV infection has proved challenging to study, in part because of the difficulty in determining onset of infection. In most patients, the disease is believed to have an indolent course for as long as 2 decades; cirrhosis has developed in 20% to 40% of patients in studies with at least 10 to 20 years of follow-up. ^, Currently, chronic hepatitis C is the reason for 30% of liver transplantations performed in the United States. The risk of hepatocellular carcinoma in HCV-related cirrhosis is estimated to be approximately 1% to 4% per year.

Occult HCV infection is a more recently recognized entity that has two distinct types of clinical presentation. The first type occurs in patients with persistently elevated liver enzymes but negative serological test results for HCV. ^, The second type is seen in patients with positive anti-HCV serology, absence of serum HCV-RNA, and normal liver function test results. In an initial study of 100 patients with elevated liver function test results and negative HCV serology, more than half were found to have HCV-RNA in their livers by reverse transcriptase (RT)-PCR and in situ hybridization. Preliminary studies have demonstrated that patients with occult HCV infection have higher triglyceride and cholesterol levels, decreased necroinflammatory scores and fibrosis, and fewer HCV-infected hepatocytes (by in situ hybridization). ^,

Patients with hepatitis C may also be co-infected with HIV, especially high-risk individuals such as intravenous drug users. As many as 25% of HIV-infected individuals in North America are also infected with HCV. ^, Effective use of highly active antiretroviral therapy (HAART) has decreased the morbidity and mortality rates from HIV infection and increased the risk of death from other causes, such as hepatitis C liver disease.

HCV infection is associated with a variety of extrahepatic manifestations and is now thought to be responsible for most cases of essential mixed cryoglobulinemia. HCV is also strongly associated with porphyria cutanea tarda (PCT) in the United States, although there is marked geographic variation in the prevalence rate of HCV in patients with PCT. Homozygosity for the Cys282Tyr mutation in the hemochromatosis gene and HCV infection are significant risk factors for the expression of PCT, with heavy alcohol use often being a contributing factor. The characteristic birefringent, yellow-brown, needle-shaped crystals described in PCT are rarely found in routinely processed liver biopsy specimens because they are highly soluble in water.

Chronic Hepatitis C

Histologically, most cases of chronic hepatitis caused by HCV tend to be mild in terms of inflammatory activity. Dense aggregates of lymphocytes in the portal tracts are a distinctive, but not pathognomonic, feature of hepatitis C and one that is readily apparent on low-power examination (see Fig. 47.11 ). Focal interface activity, as opposed to the marked interface activity typically seen in autoimmune hepatitis, is typical of hepatitis C. Bile duct infiltration by lymphocytes and steatosis can also be seen. The degree of bile duct injury in hepatitis C is usually mild, and duct loss does not occur ( Fig. 47.24 ). Steatosis in hepatitis C is usually macrovesicular; it is associated both with infection by HCV genotype 3, in which the virus is thought to be directly steatogenic, and with metabolic aberrations including insulin resistance in patients with chronic hepatitis C. Steatosis and insulin resistance are associated with more severe fibrosis, poor treatment response, and increased risk of hepatocellular carcinoma in patients with chronic hepatitis C ( Fig. 47.25 ). Nonnecrotizing granulomas occur in a small percentage of cases, but other concurrent causes of granulomas should always be excluded. The presence of scattered lobular acidophil bodies is a common feature of chronic hepatitis C. Mallory hyaline-like cytoplasmic inclusions have also been reported and have been associated with progression of fibrosis. Immunoperoxidase staining for HCV has been reported in paraffin-embedded tissue, but these stains are difficult to interpret and therefore are not often used in routine clinical practice.

Like hepatitis B, there is a rare variant of hepatitis C that can occur posttransplantation called fibrosing cholestatic hepatitis C . This rapidly progressive form is characterized by periportal sinusoidal fibrosis, bile ductular reaction, and hepatocyte swelling with lobular disarray. It can be difficult to distinguish from large bile duct obstruction. Fibrosing cholestatic hepatitis C is more likely to have more lobular disarray and periportal sinusoidal fibrosis. On the other hand, large duct obstruction is more likely to have periportal copper deposition that is usually seen in long-standing bile duct obstruction and have CK7+ intermediate hepatobiliary cells.

Treatment of Chronic Hepatitis C

Standard therapy for chronic HCV infection historically included the use of pegylated interferon and ribavirin, ^, but the advent of direct acting antiviral (DAA) therapies has revolutionized HCV treatment. In fact, HCV is no longer the most common cause of end-stage liver disease requiring liver transplant, decreasing from 24% of all adult liver transplant recipients in 2014 to just 12% in 2017. DAAs directly act to inhibit the protein components of the HCV virus, with four main categories based on their target: NS3/4A protease inhibitors, nucleotide NS5B polymerase inhibitors, nonnucleoside NS5B polymerase inhibitors, and NS5A replication complex inhibitors. The goal of treating HCV is now to cure the infection by achieving a sustained virological response (SVR), defined as undetectable HCV RNA 12 weeks (SVR12) or 24 weeks (SVR24) after completion of therapy. The cure rate demonstrated by the latest generation of DAAs approaches nearly 100% in treatment-naïve patients.

Pathologists should be aware of several important clinical issues pertinent to the DAA era. First, in the context of transplant patients, persistent histological changes of active HCV identical to pretreatment biopsies can be seen even after completion of treatment and documented evidence of SVR. ^, Hence, pathologists should not automatically diagnose these histological findings as “recurrent hepatitis C” infection. Second, the risk of HCC still exists in DAA-treated patients with SVR, particularly in cirrhotic patients, where the risk of HCC is almost five-fold higher than similarly treated patients without cirrhosis. Finally, liver biopsy for mere grading and staging HCV has become much less common and is more likely to be reserved for more complex clinical questions, such as whether or not there are concomitant diseases such as nonalcoholic steatohepatitis or autoimmune hepatitis.

Combined Viral Infections

Combined infections with HBV and HCV are not uncommon, occurring in more than 10% of patients with hepatitis B. In some patients, superinfection is associated with viral interference, which results in suppression of the preexisting virus by the more recently acquired virus. If coreplication of both HCV and HBV does occur, as evidenced by the presence of nucleic acids from both viruses, liver disease is likely to be more active and to show faster progression. The histological features of hepatitis C often predominate in liver biopsy specimens.

Co-infection with HCV or HBV (or both) and HIV is also common. Histological evaluation of liver biopsy specimens is complicated by the fact that HIV may directly affect the liver, and HAART also causes hepatotoxicity. Early studies of co-infected individuals showed an increased severity of liver disease, including necroinflammatory scores and fibrosis, compared with patients infected by HCV alone. However, subsequent studies showed that after stratification of patients by the status of their liver function test results, there were no significant differences in the degree of inflammation and fibrosis in co-infected versus solely HCV-infected individuals. More recently, the severity of liver biopsy changes has been associated with HIV RNA levels at the time of biopsy.

Hepatitis D

HDV, also known as the delta agent, is a small, defective RNA virus that requires HBsAg for packaging and transmission to cause infection and tissue injury. As such, HDV infection will always occur with HBV, either by co-infection or superinfection. It is spread by mechanisms similar to those that transmit HBV. HDV infection can cause acute or chronic hepatitis. Co-infection or superinfection can cause fulminant hepatic failure. HDV infection should be suspected in all patients with hepatitis B in whom severe exacerbation of disease activity develops. The finding of anti-HDV antibody in a patient who is seropositive for HBsAg is diagnostic. Three genotypes are recognized. In general, the histological features of HDV infection are not distinctive, but HDV is associated with more pronounced necroinflammatory activity, and more rapid progression, than is seen in patients with isolated HBV infection. Microvesicular fat may be present in severe cases. Delta antigen can be demonstrated by immunohistochemical means and is located primarily in hepatocyte nuclei.