Hepatitis A (formerly known as infectious hepatitis) is an acute infectious disease of the liver caused by the hepatitis A virus (HAV),which is most commonly transmitted by the fecal-oral route via contaminated food or drinking water. Every year, approximately 10 million people worldwide are infected with the virus.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.
In developing countries, and in regions with poor hygiene standards, the incidence of infection with this virus is high and the illness is usually contracted in early childhood. HAV has also been found in
samples taken to study ocean water quality.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 the indigenous population. 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. Hepatitis A does not have a chronic stage, is not progressive, and does not cause permanent liver damage. Following infection, the immune system makes antibodies against HAV that confer immunity against future infection. The disease can be prevented by vaccination, and hepatitis A vaccine has been proven effective in controlling outbreaks worldwide.
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, (theincubation period), after the initial infection.] Symptoms can return over the following 6–9 months and include:
Cause
Diagnosis
Serum IgG, IgM and ALT following Hepatitis A virus infection
Although HAV is excreted in the feces towards the end of the incubation period, specific diagnosis is made by the detection of HAV-specificIgM antibodies in the blood.[10] 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. 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. Hepatitis A virus is present in the blood, (viremia), and feces of infected people up to two weeks before clinical illness develops.
Treatment
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. Approximately 6–10% of people diagnosed with hepatitis A may experience one or more symptomatic relapse(s) for up to 40 weeks after contracting this disease.
Prevention.
Hepatitis A can be prevented by vaccination, good hygiene and sanitation.[1][12] Hepatitis A is also one of the main reasons not to surf or go in the ocean after rains in coastal areas that are known to have bad runoff. The vaccine protects against HAV in more than 95% of cases for 10 years. It contains inactivated Hepatitis A virus providing active immunity against a future infection. 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.
The vaccine is given by injection into the muscle of the upper arm. 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 up to twenty years.
Transmission
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,and ingestion ofshellfish cultivated in polluted water is associated with a high risk of infection. Approximately 40% of all acute viral hepatitis is caused by HAV. 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 60oC. 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%, 37oC, 72 hours), peracetic acid (2%, 4 hours), beta-propiolactone (0.25%, 1 hour), and UV radiation (2 μW/cm2/min).
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