Hepatitis A is an infectious disease of the liver caused by the hepatitis A virus (HAV).Many cases have few or no symptoms, especially in the young.The time between infection and symptoms, in those who develop them, is between two and six weeks.
When symptoms occur, they typically last eight weeks and may include nausea, vomiting, diarrhea, jaundice, fever, and abdominal pain. Around 10–15% of people experience a recurrence of symptoms during the six months after the initial infection.
Acute liver failure may rarely occur, with this being more common in the elderly.
It is usually spread by eating food or drinking water contaminated with infected feces.Shellfish which have not been sufficiently cooked are a relatively common source.It may also be spread through close contact with an infectious person. While children often do not have symptoms when infected, they are still able to infect others.
After a single infection, a person is immune for the rest of his or her life. Diagnosis requires blood testing, as the symptoms are similar to those of a number of other diseases.It is one of five known hepatitis viruses: A, B, C, D, and E.
Signs and symptoms
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.
About 90% of children do not have symptoms. The time between infection and symptoms, in those who develop them, is between 2 and 6 weeks with an average of 28 days.
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.
Symptoms usually last less than 2 months, although some people can be ill for as long as 6 months:
- 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 colour
Diarrhea
Light, or clay-coloured faeces (acholic faeces)
Abdominal discomfort.
Diagnosis
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.
IgM antibody is only present in the blood following an acute hepatitis A infection. It is detectable from 1-2 weeks after the initial infection and persists for up to 14 weeks.
The presence of 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 this antibody.
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 damaged by the virus.
Hepatovirus A is present in the blood (viremia) and feces of infected people up to 2 weeks before clinical illness develops.
Prevention
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.
The vaccine was introduced in 1992 and was initially recommended for persons at high risk. Since then, Bahrain and Israel have embarked on eradication programmes. Australia, China, Belarus, Italy, Spain, and the United States have started similar programmes.
The incidence of hepatitis A where widespread vaccination has been practised has decreased dramatically. In China and the United States, the incidence of hepatitis A has decreased by 90% since 1990.
In the United States, vaccination of children is recommended at 1 and 2 years of age.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. The CDC recommends vaccination against infection for men who have sex with men.
Treatment
No specific treatment for hepatitis A is known. Recovery from symptoms following infection may take several weeks or months.
