| Hepatitis A | |
|---|---|
| Classification and external resources | |
| ICD-10 | B15 |
| ICD-9 | 070.0, 070.1 |
| DiseasesDB | 5757 |
| MedlinePlus | 000278 |
| eMedicine | med/991 ped/977 |
| MeSH | D006506 |
Hepatitis A (formerly known as infectious hepatitis and epidemical virus) is an acute infectious disease of the liver caused by the hepatitis A virus (Hep A),[1] an RNA virus, usually spread the fecal-oral route; transmitted person-to-person by ingestion of contaminated food or water or through direct contact with an infectious person. Tens of millions of individuals worldwide are estimated to become infected with Hep A each year.[2] The time between infection and the appearance of the symptoms (the incubation period) is between two and six weeks and the average incubation period is 28 days.[3]
In developing countries, and in regions with poor hygiene standards, the incidence of infection with this virus is high[4] and the illness is usually contracted in early childhood. As incomes rise and access to clean water increases, the incidence of HAV decreases.[5] Hepatitis A infection causes no clinical signs and symptoms in over 90% of infected children and since the infection confers lifelong immunity, the disease is of no special significance to those infected early in life. In Europe, the United States and other industrialized countries, on the other hand, the infection is contracted primarily by susceptible young adults, most of whom are infected with the virus during trips to countries with a high incidence of the disease[3] or through contact with infectious persons.
HAV infection produces a self-limited disease that does not result in chronic infection or chronic liver disease. However, 10–15% of patients might experience a relapse of symptoms during the 6 months after acute illness. Acute liver failure from Hepatitis A is rare (overall case-fatality rate: 0.5%). The risk for symptomatic infection is directly related to age, with >80% of adults having symptoms compatible with acute viral hepatitis and the majority of children having either asymptomatic or unrecognized infection.[6] Antibody produced in response to HAV infection persists for life and confers protection against reinfection. The disease can be prevented by vaccination, and hepatitis A vaccine has been proven effective in controlling outbreaks worldwide.[3]
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Early symptoms of hepatitis A infection can be mistaken for influenza, but some sufferers, especially children, exhibit no symptoms at all. Symptoms typically appear 2 to 6 weeks, (the incubation period), after the initial infection.[7]
Symptoms usually last less than 2 months, although some people can be ill for as long as 6 months.:[8]
| Hepatitis A | |
|---|---|
| Electron micrograph of hepatitis A virions. | |
| Virus classification | |
| Group: | Group IV ((+)ssRNA) |
| Family: | Picornaviridae |
| Genus: | Hepatovirus |
| Species: | Hepatitis A virus |
Following ingestion, HAV enters the bloodstream through the epithelium of the oropharynx or intestine.[9] The blood carries the virus to its target, the liver, where it multiplies within hepatocytes and Kupffer cells (liver macrophages). Virions are secreted into the bile and released in stool. HAV is excreted in large quantities approximately 11 days prior to appearance of symptoms or anti-HAV IgM antibodies in the blood. The incubation period is 15–50 days and mortality is less than 0.5%. Within the liver hepatocytes the RNA genome is released from the protein coat and is translated by the cell's own ribosomes. Unlike other members of the Picornaviruses this virus requires an intact eukaryote initiating factor 4G (eIF4G) for the initiation of translation.[10] The requirement for this factor results in an inability to shut down host protein synthesis unlike other picornaviruses. The virus must then inefficiently compete for the cellular translational machinery which may explain its poor growth in cell culture. Presumably for this reason the virus has strategically adopted a naturally highly deoptimized codon usage with respect to that of its cellular host. Precisely how this strategy works is not quite clear yet.
There is no apparent virus-mediated cytotoxicity presumably because of the virus' own requirement for an intact eIF4G and liver pathology is likely immune-mediated.
The Hepatitis virus (HAV) is a Picornavirus; it is non-enveloped and contains a single-stranded RNA packaged in a protein shell.[11] There is only one serotype of the virus, but multiple genotypes exist.[12] Codon use within the genome is biased and unusually distinct from its host. It also has a poor internal ribosome entry site[13] In the region that codes for the HAV capsid there are highly conserved clusters of rare codons that restrict antigenic variability.[14]
The virus spreads by the fecal-oral route and infections often occur in conditions of poor sanitation and overcrowding. Hepatitis A can be transmitted by the parenteral route but very rarely by blood and blood products. Food-borne outbreaks are not uncommon,[15] and ingestion of shellfish cultivated in polluted water is associated with a high risk of infection.[16] Approximately 40% of all acute viral hepatitis is caused by HAV.[9] Infected individuals are infectious prior to onset of symptoms, roughly 10 days following infection. The virus is resistant to detergent, acid (pH 1), solvents (e.g., ether, chloroform), drying, and temperatures up to 60 °C. It can survive for months in fresh and salt water. Common-source (e.g., water, restaurant) outbreaks are typical. Infection is common in children in developing countries, reaching 100% incidence, but following infection there is life-long immunity. HAV can be inactivated by: chlorine treatment (drinking water), formalin (0.35%, 37 °C, 72 hours), peracetic acid (2%, 4 hours), beta-propiolactone (0.25%, 1 hour), and UV radiation (2 μW/cm2/min).
Although HAV is excreted in the feces towards the end of the incubation period, specific diagnosis is made by the detection of HAV-specific IgM antibodies in the blood.[17] IgM antibody is only present in the blood following an acute hepatitis A infection. It is detectable from one to two weeks after the initial infection and persists for up to 14 weeks. The presence of IgG antibody in the blood means that the acute stage of the illness is past and the person is immune to further infection. IgG antibody to HAV is also found in the blood following vaccination and tests for immunity to the virus are based on the detection of this antibody.[17]
During the acute stage of the infection, the liver enzyme alanine transferase (ALT) is present in the blood at levels much higher than is normal. The enzyme comes from the liver cells that have been damaged by the virus.[18]
Hepatitis A virus is present in the blood, (viremia), and feces of infected people up to two weeks before clinical illness develops.[18]
Hepatitis A can be prevented by vaccination, good hygiene and sanitation.[1][19]
The vaccine protects against HAV in more than 95% of cases for longer than 20 years. It contains inactivated hepatitis A virus providing active immunity against a future infection.[20][21] The vaccine was first phased in 1996 for children in high-risk areas, and in 1999 it was spread to areas with elevating levels of infection.[22]
The vaccine is given by injection. An initial dose provides protection starting two to four weeks after vaccination; the second booster dose, given six to twelve months later, provides protection for over twenty years.[20][22]
There is no specific treatment for hepatitis A. Sufferers are advised to rest, avoid fatty foods and alcohol (these may be poorly tolerated for some additional months during the recovery phase and cause minor relapses), eat a well-balanced diet, and stay hydrated.[23]
The United States Centers for Disease Control and Prevention (CDC) in 1991 reported a low mortality rate for hepatitis A of 4 deaths per 1000 cases for the general population but a higher rate of 17.5 per 1000 in those aged 50 and over. The risk of death from acute liver failure following HAV infection increases with age and when the person has underlying chronic liver disease.
Young children who are infected with hepatitis A typically have a milder form of the disease, usually lasting from 1–3 weeks, whereas adults tend to experience a much more severe form of the disease.[15]
Antibodies to HAV (anti-HAV) in the blood are a marker of past or current infection. High-income regions (Western Europe, Australia, New Zealand, Canada, the United States, Japan, the Republic of Korea, and Singapore) have very low HAV endemicity levels and a high proportion of susceptible adults, low-income regions (sub-Saharan Africa and parts of South Asia) have high endemicity levels and almost no susceptible adolescents and adults, and most middle-income regions have a mix of intermediate and low endemicity levels. Anti-HAV prevalence suggest that middle-income regions in Asia, Latin America, Eastern Europe, and the Middle East currently have an intermediate or low level of endemicity. The countries in these regions may have an increasing burden of disease from hepatitis A.[24]
There were 30,000 cases of Hepatitis A reported to the CDC in the U.S. in 1997. The agency estimates that there were as many as 270,000 cases each year from 1980 through 2000.[25]
The most widespread hepatitis A outbreak in the 2003 United States hepatitis outbreak afflicted at least 640 people (killing four) in north-eastern Ohio and south-western Pennsylvania in late 2003. The outbreak was blamed on tainted green onions at a restaurant in Monaca, Pennsylvania.[26] In 1988, 300,000 people in Shanghai, China were infected with HAV after eating clams from a contaminated river.[9]
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