Hepatitis E Cleveland Clinic
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William D. Carey, MD A multitude of viruses may cause hepatic inflammation but 5, designated A, B, C, D, and E primarily infect the liver and produce hepatitis as their primary clinical manifestation (Table 1). Historically, hepatitis E virus (HEV) has been known to cause acute hepatic inflammation almost exclusively. Usually, in a self-limiting fashion that may infrequently progress to fulminant hepatitis. Transmission is predominantly through the fecal-oral route, through contaminated water. In such ways, it has been known to cause epidemics in high prevalence areas.
Global†
Acute
Chronic United States
Acute
Chronic HAV 1/4 N/A 21000 N/A HBV 4 240 38000 1.4 HCV 3-4 150 16000 3.9 HEV 20/3* Unknown Unknown Unknown † All numbers are reported in millions.
* 20 million new infections and 3 million cases of acute hepatis. Hepatitis data can be found at www.who.int/topics/hepatitis/factsheets/en/. In none endemic areas the prevalence of the disease used to be practically nil. However, in recent years there has been a major increase in the number of cases. Recent seroprevalence reports estimate that about one-third of the world population is positive for anti-HEV IgG antibody; a statistic that arguably makes HEV the new leading cause of acute hepatitis in the world and a major universal public health burden. Next: Definition Definition
7.5kB OrF-1
ORF-3 OrF-2 Melthyltransferase Cysteine protein RNA helicase RNA polymerase Phosophoprotein Capsid protein The virus was previously recognized as part of the Calciviridae family in the genus Calcivirus, but recently it was reclassified into the Hepeviridae family in the Hepevirus genus. Namely, the Hepeviridae family consists of 2 species: first the mammalian HEV strains, which affects humans and pigs typically; and second the avian strain, which is accountable for big liver-spleen disease in chicken and can also affect other birds.13 Mammalian strains are grouped into 4 different genotypes, 1 through 4, each with several subtypes and approximately about an 80% homology among genotypes. Different genotypes have marked differences in epidemiology. Genotype 1 and 2 are highly prevalent in endemic areas causing epidemics among humans. Both have high mortality rates in pregnant women, a trait also shared by genotype 4. Genotype 3 is most prevalent in developed countries. It has been shown to be transmitted by animal contact or by consuming contaminated aliments. It is typically seen in individuals aged over 40 years and is known to cause severe disease in immunocompromised individuals in whom it can become chronic. Pigs commonly harbor genotypes 3 and 4. Avian strains have a 50% homology with the mammalian strains. There are 3 distinct genotypes: Genotype 1 was identified in Australia, genotype 2 is most common in the US, and genotype 3 was identified in Europe and China. Avian strains are similar to swine strains since they have the ability to cross infect closely related species (ie, turkeys). Experimentally they have not been shown to infect monkeys, and so they probably less likely to infect humans. Previous: Background Next: Epidemiology Epidemiology
Figure 4. Hepatitis E particles in stool. Hepatitis E virus (HEV), the majore causative agent of enterically transmitted non-A, non-B hepatitis worldwide, is a spherical, nonenveloped, single-stranded RNA virus that is approximately 32 to 34 nm in diameter. From the Centers for Disease Control: Hepatitis E Virus, 2007. Similar to hepatitis A, HEV is most often a self-limited disease; immunity develops, and no second attack occurs. The disease is often cholestatic, with elevated bilirubin and alkaline phosphatase levels. On average, it occurs more commonly in the older population and severe disease, including fulminant hepatitis and death, occur more often in HEV than in other types of hepatitis. Mortality rates range from 0% to 10%, but it is usually less than 1%. In pregnant women, infection has been associated with development fulminant liver failure and mortality can reach 25%. Modes of transmission include: fecal-oral route, food borne, from exposure to infected animals, via blood transfusion, solid organ transplantation, and lastly via vertical transmission. Prolonged viremia and fecal shedding are uncommon. However, in developed countries progression to chronic disease and cirrhosis has been reported in older patients, those with pre-existing chronic liver disease, and the immunosuppressed. Previous: Epidemiology Next: Signs and Symptoms Signs and Symptoms
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Hepatitis E
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Sandra Rodriguez, MDWilliam D. Carey, MD A multitude of viruses may cause hepatic inflammation but 5, designated A, B, C, D, and E primarily infect the liver and produce hepatitis as their primary clinical manifestation (Table 1). Historically, hepatitis E virus (HEV) has been known to cause acute hepatic inflammation almost exclusively. Usually, in a self-limiting fashion that may infrequently progress to fulminant hepatitis. Transmission is predominantly through the fecal-oral route, through contaminated water. In such ways, it has been known to cause epidemics in high prevalence areas.
Table 1 Comparison of the worldwide burden of hepatitis
Global†
Acute
Chronic United States
Acute
Chronic HAV 1/4 N/A 21000 N/A HBV 4 240 38000 1.4 HCV 3-4 150 16000 3.9 HEV 20/3* Unknown Unknown Unknown † All numbers are reported in millions.
* 20 million new infections and 3 million cases of acute hepatis. Hepatitis data can be found at www.who.int/topics/hepatitis/factsheets/en/. In none endemic areas the prevalence of the disease used to be practically nil. However, in recent years there has been a major increase in the number of cases. Recent seroprevalence reports estimate that about one-third of the world population is positive for anti-HEV IgG antibody; a statistic that arguably makes HEV the new leading cause of acute hepatitis in the world and a major universal public health burden. Next: Definition Definition
Definition
HEV is a small, spherical, non-enveloped virus that is 32 to 34 nm in diameter. It carries a single stranded RNA genome that is 7.2 kB in length and contains 3 open reading frames (ORFs). ORF1 encodes for messenger RNA which codes for non-structural proteins that are required for viral replication. ORF2 encodes for the viral capsid that is responsible for activation of the immune system. ORF3 encodes for small non-structural proteins that contribute to HEV replication and pathogenesis. The genome contains short non-coding regions at the 5' and 3' ends, and in between the ORFs which are discontinuous and partially overlapping (Figure 1).Figure 1. Hepatitis E Virus Generic Map
2kB7.5kB OrF-1
ORF-3 OrF-2 Melthyltransferase Cysteine protein RNA helicase RNA polymerase Phosophoprotein Capsid protein The virus was previously recognized as part of the Calciviridae family in the genus Calcivirus, but recently it was reclassified into the Hepeviridae family in the Hepevirus genus. Namely, the Hepeviridae family consists of 2 species: first the mammalian HEV strains, which affects humans and pigs typically; and second the avian strain, which is accountable for big liver-spleen disease in chicken and can also affect other birds.13 Mammalian strains are grouped into 4 different genotypes, 1 through 4, each with several subtypes and approximately about an 80% homology among genotypes. Different genotypes have marked differences in epidemiology. Genotype 1 and 2 are highly prevalent in endemic areas causing epidemics among humans. Both have high mortality rates in pregnant women, a trait also shared by genotype 4. Genotype 3 is most prevalent in developed countries. It has been shown to be transmitted by animal contact or by consuming contaminated aliments. It is typically seen in individuals aged over 40 years and is known to cause severe disease in immunocompromised individuals in whom it can become chronic. Pigs commonly harbor genotypes 3 and 4. Avian strains have a 50% homology with the mammalian strains. There are 3 distinct genotypes: Genotype 1 was identified in Australia, genotype 2 is most common in the US, and genotype 3 was identified in Europe and China. Avian strains are similar to swine strains since they have the ability to cross infect closely related species (ie, turkeys). Experimentally they have not been shown to infect monkeys, and so they probably less likely to infect humans. Previous: Background Next: Epidemiology Epidemiology
Epidemiology
Figure 2: Geographic distribution of hepatitis E-outbreaks or confirmed infection in more than 25% of cases of sporadic non-ABC hepatitis. Global HEV prevalence is on the rise. Approximately 2 billion people worldwide are positive for anti-HEV IgG antibody. The World Health Organization (WHO) reported that approximately 20 million people are infected yearly, and of those cases approximately 3 million progress to an acute hepatitis syndrome. There are about 70, 000 deaths related to HEV worldwide per year. Genotype 1 is endemic to Central and Southeast Asia, Africa and Central America where it is known to cause epidemics. The virus has also been isolated in low endemic areas among travelers from high prevalence regions. Genotype 2 was first identified in Mexico, and subsequently has been reported from Nigeria and Chad. Genotype 2 is not as commonly a cause of epidemic compared with genotype 1. Genotypes 3 and 4 are common in the swine population in developed countries; and are emerging as significant causes of human infection. The first case of a human infected with genotype 3 was identified in the United States and subsequently in Europe, Australia, and Japan. Genotype 4 has been found in sporadic cases in Vietnam, China, and Taiwan. (Figure 2). The highest seroprevalence of HEV is seen in countries of low socioeconomic status and poor sanitation; reportedly 20% to 40%.4 Outbreaks happen commonly during rainy season, when potable water is contaminated by flooding18 or with disposal of fecal waste into usable water sources. In urban underdeveloped areas, outbreaks commonly occur through water conduits that pass through soil that is contaminated with human excrements. Lastly, there is also a large proportion of sporadic HEV cases in endemic areas. The mode of transmission or risk factors is not known and whether animal spread plays a role remains a mystery. In developed countries, human HEV was considered uncommon, with a prevalence of less than 1%. However, rates of anti HEV antibody within the general population have increased significantly; 2% in Europe and 1%-3% in the United States, with up to 20% prevalence in certain high-risk groups. The majority of cases are sporadic, and high risk populations include farmers, animal butchers, veterinarians, persons that handle animal products or consume of undercooked meat. As such, animals compose a key reservoir for HEV infection in the first world, and probably accounts for increase in prevalence. Sporadic cases are more common in patients aged 60 years or older, with a 3-to-1 male-to-female ratio. The primary mode of transmission is foodborne from ingestion of contaminated products or from direct contact with an infected animal. In the US, human HEV strains have been genetically isolated from pigs, chickens, rabbits, rats, and fish.12,28. The highest prevalence is among the swine population with genotype 3; genotype 4 has been identified in swine in other countries. Ming et al. found HEV to be ubiquitous in the population of swine aged older than 3 months herds throughout the Midwestern US, with a prevalence of 80% to 100% in some groups. In the same study, it was noted that the ORF2 of swine HEV had a 90% amino acid sequence similarity with human HEV strains and that ORF3 had 80% amino acid sequence similarity with human HEV strains prevalent in the United States. Feagins et al reported that 11% of the commercial pig livers sold in local grocery stores are contaminated by infectious HEV. These statistics probably account for the 21% reported prevalence of anti-IgG HEV in the US. Similar statistics have been reported in Europe and Japan where sporadic cases have been directly linked to undercooked pig livers. Lastly, evidence also exists to implicate shellfish as a foodborne source of infection and a public health concern. This is made evident by reported outbreaks of genotype 3 among 33 cruise ship passengers who consumed contaminated shellfish. In addition, 2 cases of HEV were identified in the United Kingdom in 2005, both found to be related to consumption of shellfish. The mechanism of contamination seems to be related to agricultural waste spills that mix with shellfish harvesting waters. Previous: Definition Next: Pathophysiology and Natural History Pathophysiology and Natural HistoryPathophysiology and Natural History
In an acute infection the incubation period ranges from 15 to 60 days, through which viremia arises. Anti-HEV antibody (IgM) appears soon after the onset of the clinical infection. Anti-HEV IgG appears soon after that and can remain detectable for as long as 20 months (Figure 3). HEV RNA is detected in stool as early as 1 week before the onset of clinical illness and persists for 1 to 2 weeks afterward, during which stools are highly infectious. (Figure 3 and 4) Figure 3. HEV Serologic CourseFigure 4. Hepatitis E particles in stool. Hepatitis E virus (HEV), the majore causative agent of enterically transmitted non-A, non-B hepatitis worldwide, is a spherical, nonenveloped, single-stranded RNA virus that is approximately 32 to 34 nm in diameter. From the Centers for Disease Control: Hepatitis E Virus, 2007. Similar to hepatitis A, HEV is most often a self-limited disease; immunity develops, and no second attack occurs. The disease is often cholestatic, with elevated bilirubin and alkaline phosphatase levels. On average, it occurs more commonly in the older population and severe disease, including fulminant hepatitis and death, occur more often in HEV than in other types of hepatitis. Mortality rates range from 0% to 10%, but it is usually less than 1%. In pregnant women, infection has been associated with development fulminant liver failure and mortality can reach 25%. Modes of transmission include: fecal-oral route, food borne, from exposure to infected animals, via blood transfusion, solid organ transplantation, and lastly via vertical transmission. Prolonged viremia and fecal shedding are uncommon. However, in developed countries progression to chronic disease and cirrhosis has been reported in older patients, those with pre-existing chronic liver disease, and the immunosuppressed. Previous: Epidemiology Next: Signs and Symptoms Signs and Symptoms