Hepatitis A

What is hepatitis A?

Hepatitis A, also known as infectious hepatitis, is an acute infectious disease of the liver caused by Hepatitis A virus, 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 approaches 100% and the illness is usually contracted in early childhood. Hepatitis A infection causes no clinical signs and symptoms in over 90% of these children and since the infection confers lifelong immunity, the disease is of no special significance to the indigenous population.

Hepatitis A does not have a chronic stage and does not cause permanent liver damage. Following infection, the immune system makes antibodies against the hepatitis A virus that confer immunity against future infection. The disease can be prevented by vaccination and hepatitis A vaccine has been proved effective in controlling outbreaks.

Virus

The Hepatitis virus (HAV) is a Picornavirus; it is non-enveloped and contains a single-stranded RNA packaged in a protein shell. There is only one type of the virus.

Pathogenesis

Following ingestion, HAV enters the bloodstream through the epithelium of the oropharynx or intestine. The blood carries the virus to its target, the liver, where it lives and multiplies within hepatocytes and Kupffer cells (i.e., liver macrophages). There is no apparent virus-mediated cytotoxicity, and liver pathology is likely immune-mediated. Virions are secreted into the bile and released in stool. HAV is excreted in large quantities approimately 11 days prior to appearance of symptoms or anti-HAV IgM antibodies in the blood.The incubation period is 15-50 days.

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 common, and ingestion of shellfish 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.

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.

Symptoms can return over the following 6-9 months which include:

• Fever
• Abdominal pain
• Nausea
• Diarrhea
• Appetite loss
• Depression
• Fatigue
• Weight loss
  
• Itching
  
• Jaundice, a yellowing of the skin or whites of the eyes
• Sharp pains in the right-upper quadrant of the abdomen

Diagnosis

(Serum IgG, IgM and ALT following Hepatitis A virus infection)

Although the virus is excreted in the feces towards the end of the incubation period, specific diagnosis is made by the detection of Hepatitis A virus specific IgM antibodies in the blood. 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, eat a well-balanced diet, and stay hydrated. Approximately 15% of people diagnosed with hepatitis A may experience one or more symptomatic relapse(s) for up to 24 months after contracting this disease.

Prognosis

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.Death usually occurs when the patient contracts Hepatitis A while already suffering from another form of Hepatitis, such as Hepatitis B or Hepatitis C or AIDS.

Prevention

Hepatitis A can be prevented by vaccination, good hygiene and sanitation.

Vaccine

Hepatitis A vaccines protect against the virus. Vaccines contain inactivated Hepatitis A virus providing active immunity against a future infection.