Hepatitis A

Source: Wikipedia, the free encyclopedia.
Hepatitis A
Other namesInfectious hepatitis
Supportive care, liver transplantation[1]
Frequency114 million symptomatic and nonsymptomatic (2015)[4]
Deaths11,200[5]

Hepatitis A is an infectious disease of the liver caused by Hepatovirus A (HAV);[6] it is a type of viral hepatitis.[7] Many cases have few or no symptoms, especially in the young.[1] The time between infection and symptoms, in those who develop them, is 2–6 weeks.[2] When symptoms occur, they typically last 8 weeks and may include nausea, vomiting, diarrhea, jaundice, fever, and abdominal pain.[1] Around 10–15% of people experience a recurrence of symptoms during the 6 months after the initial infection.[1] Acute liver failure may rarely occur, with this being more common in the elderly.[1]

It is usually spread by eating food or drinking water contaminated with infected feces.

immune for the rest of their life.[9] Diagnosis requires blood testing, as the symptoms are similar to those of a number of other diseases.[1] It is one of five known hepatitis viruses: A, B, C, D, and E
.

The hepatitis A vaccine is effective for prevention.[10][11][12] [1][3][needs update] Some countries recommend it routinely for children and those at higher risk who have not previously been vaccinated.[1][13] It appears to be effective for life.[1] Other preventive measures include hand washing and properly cooking food.[1] No specific treatment is available, with rest and medications for nausea or diarrhea recommended on an as-needed basis.[1] Infections usually resolve completely and without ongoing liver disease.[1] Treatment of acute liver failure, if it occurs, is with liver transplantation.[1]

Globally, around 1.4 million symptomatic cases occur each year

developing world, about 90% of children have been infected by age 10, thus are immune by adulthood.[13] It often occurs in outbreaks in moderately developed countries where children are not exposed when young and vaccination is not widespread.[13] Acute hepatitis A resulted in 11,200 deaths in 2015.[5] World Hepatitis Day occurs each year on July 28 to bring awareness to viral hepatitis.[13]

Signs and symptoms

Early symptoms of hepatitis A infection can be mistaken for influenza, but some people, especially children, exhibit no symptoms at all. Symptoms typically appear 2–6 weeks (the incubation period) after the initial infection.[14] About 90% of children do not have symptoms. The time between infection and symptoms, in those who develop them, is 2–6 weeks, with an average of 28 days.[2]

The risk for symptomatic infection is directly related to age, with more than 80% of adults having symptoms compatible with acute viral hepatitis and the majority of children having either asymptomatic or unrecognized infections.[15]

Symptoms usually last less than 2 months, although some people can be ill for as long as 6 months:[16]

  • Fatigue
  • Fever
  • Nausea
  • Appetite loss
  • Jaundice, a yellowing of the skin or the whites of the eyes owing to hyperbilirubinemia
  • Bile is removed from the bloodstream and excreted in the urine, giving it a dark amber color
  • Diarrhea
  • Light or clay-colored faeces (acholic faeces)
  • Abdominal discomfort[17]

Extrahepatic manifestations

red cell aplasia, pancreatitis and generalized lymphadenopathy are the possible extrahepatic manifestations. Kidney failure and pericarditis are very uncommon.[18] If they occur, they show an acute onset and disappear upon resolution of the disease.[citation needed
]

Virology

Hepatovirus A
Electron micrograph of "Hepatovirus A" virions
Electron micrograph of Hepatovirus A virions
Virus classification Edit this classification
(unranked): Virus
Realm: Riboviria
Kingdom: Orthornavirae
Phylum: Pisuviricota
Class: Pisoniviricetes
Order: Picornavirales
Family:
Picornaviridae
Genus: Hepatovirus
Species:
Hepatovirus A
Synonyms
  • Hepatitis A virus[19]
  • Human hepatitis A virus[20]
  • Simian hepatitis A virus[20]

Taxonomy

Hepatovirus A is a species of

Picornaviridae, genus Hepatovirus. Humans and other vertebrates serve as natural hosts of this genus.[21][22]

Nine members of Hepatovirus are recognized.[23] These species infect bats, rodents, hedgehogs, and shrews. Phylogenetic analysis suggests a rodent origin for human Hepatitis A.[24]

A

member virus of hepatovirus B (Phopivirus) has been isolated from a seal.[25][26] This virus shared a common ancestor with Hepatovirus A about 1800 years ago.[citation needed
]

Another hepatovirus –

Marmota himalayana.[27] This virus appears to have had a common ancestor with the primate-infecting species around 1000 years ago.[citation needed
]

Genotypes

One serotype and six different genotypes (three human and three simian) have been described.

owl monkeys. Most human isolates are of genotype I.[31]
Of genotype I isolates, subtype IA accounts for the majority.

The mutation rate in the genome has been estimated to be 1.73–9.76 × 10−4 nucleotide substitutions per site per year.[32][33] The human strains appear to have diverged from the simian about 3600 years ago.[33] The mean age of genotypes III and IIIA strains has been estimated to be 592 and 202 years, respectively.[33]

Structure

Hepatovirus A is a

Codon use within the genome is biased and unusually distinct from its host. It also has a poor internal ribosome entry site.[35] In the region that codes for the HAV capsid, highly conserved clusters of rare codons restrict antigenic variability.[21][36]

Genus Structure Symmetry Capsid Genomic arrangement Genomic segmentation
Hepatovirus Icosahedral Pseudo T=3 Nonenveloped Linear Monopartite

Replication cycle

Vertebrates such as humans serve as the natural hosts. Transmission routes are fecal-oral and blood.[21]

Following ingestion, HAV enters the bloodstream through the

antibodies in the blood. The incubation period is 15–50 days and risk of death in those infected is less than 0.5%.[citation needed
]

Within the liver hepatocytes, the

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. Aragonès et al. (2010) theorize that the virus has evolved a naturally highly deoptimized codon usage with respect to that of its cellular host in order to negatively influence viral protein translation kinetics and allow time for capsid proteins to fold optimally.[38]

No apparent virus-mediated cytotoxicity occurs, presumably because of the virus' own requirement for an intact eIF4G, and liver pathology is likely immune-mediated.

Genus Host details Tissue tropism Entry details Release details Replication site Assembly site Transmission
Hepatovirus Humans; vertebrates Liver Cell receptor endocytosis Lysis Cytoplasm Cytoplasm Oral-fecal; blood

Transmission

The virus spreads by the

parenteral route, but very rarely by blood and blood products. Food-borne outbreaks are common,[39] and ingestion of shellfish cultivated in polluted water is associated with a high risk of infection.[40]
About 40% of all acute viral hepatitis is caused by HAV.
UV radiation (2 μW/cm2/min). HAV can also be spread through sexual contact specifically oroanal sexual acts.[citation needed
]

In developing countries, and in regions with poor hygiene standards, the rates of infection with this virus are high[41] and the illness is usually contracted in early childhood. As incomes rise and access to clean water increases, the incidence of HAV decreases.[42] In developed countries, though, 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[2] or through contact with infectious persons.

Humans are the only natural reservoir of the virus. No known insect or other animal vectors can transmit the virus. A chronic HAV state has not been reported.[43]

Diagnosis

Serum IgG, IgM, and ALT following hepatovirus A infection

Although HAV is excreted in the feces towards the end of the incubation period, specific diagnosis is made by the detection of HAV-specific

IgG antibodies in the blood means the acute stage of the illness has passed and the person is immune to further infection. IgG antibodies to HAV are also found in the blood following vaccination, and tests for immunity to the virus are based on the detection of these antibodies.[44]

During the acute stage of the infection, the

alanine transferase (ALT) is present in the blood at levels much higher than is normal. The enzyme comes from the liver cells damaged by the virus.[45]

Hepatovirus A is present in the blood (viremia) and feces of infected people up to 2 weeks before clinical illness develops.[45]

Prevention

For information about the vaccine, its properties, and its application, see Hepatitis A vaccine.

Hepatitis A can be prevented by vaccination, good hygiene, and sanitation.[6][46]

Vaccination

The two types of vaccines contain either inactivated Hepatovirus A or a live but attenuated virus.[3] Both provide active immunity against a future infection. The vaccine protects against HAV in more than 95% of cases for longer than 25 years.[47] In the United States, the vaccine developed by Maurice Hilleman and his team was licensed in 1995,[48][49] and the vaccine was first used in 1996 for children in high-risk areas, and in 1999 it was spread to areas with elevating levels of infection.[50]

The vaccine is given by injection. An initial dose provides protection lasting one year starting 2–4 weeks after vaccination; the second booster dose, given six to 12 months later, provides protection for over 20 years.[50]

The vaccine was introduced in 1992 and was initially recommended for persons at high risk. Since then, Bahrain and Israel have embarked on elimination programmes.[51] In countries where widespread vaccination has been practised, the incidence of hepatitis A has decreased dramatically.[52][53][54][55]

In the United States, vaccination of children is recommended at 1 and 2 years of age;[1] hepatitis A vaccination is not recommended in those younger than 12 months of age.[56] It is also recommended in those who have not been previously immunized and who have been exposed or are likely to be exposed due to travel.[1] The CDC recommends vaccination against infection for men who have sex with men.[57]

Treatment

No specific treatment for hepatitis A is known. Recovery from symptoms following infection may take several weeks or months. Therapy is aimed at maintaining comfort and adequate nutritional balance, including replacement of fluids lost from vomiting and diarrhea.[17]

Prognosis

In the United States in 1991, the mortality rate for hepatitis A was estimated to be 0.015% for the general population, but ranged up to 1.8–2.1% for those aged 50 and over who were hospitalized with icteric hepatitis.[58] The risk of death from acute liver failure following HAV infection increases with age and when the person has underlying chronic liver disease.[citation needed] Liver illness can be brought on by the hepatitis C virus, also known as Hep C or HCV. While the majority of kids and teenagers recover from the initial stage of HCV infection, 60–80% of them could show symptoms of a persistent liver infection. This may result in fatalities as well as far more severe liver issues. In the US, the hepatitis C virus is responsible for over 10,000 fatalities annually.

Young children who are infected with hepatitis A typically have a milder form of the disease, usually lasting 1–3 weeks, whereas adults tend to experience a much more severe form of the disease.[39]

Epidemiology

Hepatitis A distribution 2005
  High: prevalence higher than 8%
  Intermediate: between 2% and 7%
  Low : less than 2%

Globally, symptomatic HAV infections are believed to occur in around 1.4 million people a year.[1] About 114 million infections (asymptomatic and symptomatic) occurred all together in 2015.[4] Acute hepatitis A resulted in 11,200 deaths in 2015.[5] Developed countries have low circulating levels of hepatovirus A, while developing countries have higher levels of circulation.[59] Most adolescents and adults in developing countries have already had the disease, thus are immune.[59] Adults in midlevel countries may be at risk of disease with the potential of being exposed.[59]

Countries

Over 30,000 cases of hepatitis A were reported to the CDC in the US in 1997, but the number has since dropped to less than 2,000 cases reported per year.[60]

The most widespread hepatitis A outbreak in the United States occurred in 2018, in the state of Kentucky. The outbreak is believed to have started in November 2017.[61] By July 2018 48% of the state's counties had reported at least one case of hepatitis A, and the total number of suspected cases was 969 with six deaths (482 cases in Louisville, Kentucky).[62] By July 2019 the outbreak had reached 5,000 cases and 60 deaths, but had slowed to just a few new cases per month.[61]

Another widespread outbreak in the United States, the

Anadara subcrenata) from a contaminated river.[37]
In June 2013, frozen berries sold by US retailer Costco and purchased by around 240,000 people were the subject of a recall, after at least 158 people were infected with HAV, 69 of whom were hospitalized.[65][66] In April 2016, frozen berries sold by Costco were once again the subject of a recall, after at least 13 people in Canada were infected with HAV, three of whom were hospitalized.[67] In Australia in February 2015, a recall of frozen berries was issued after at least 19 people contracted the illness following their consumption of the product.[68] In 2017, California (particularly around San Diego), Michigan, and Utah reported outbreaks of hepatitis A that have led to over 800 hospitalizations and 40 deaths.[69][70][71]

See also

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External links

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