Hepatitis A overview

# Overview
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), 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. 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. As incomes rise and access to clean water increases, the incidence of HAV decreases. 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 or through contact with infectious persons.

# Historical Perspective
Hepatitis A virus was first identified in 1973. It was classified as a separate disease from other types of hepatitis during World War II. However, its true prevalence and route of transmission would only be recognized later.  During 1995-1996, the Food and Drug Administration (FDA) approved the inactivated hepatitis A vaccines. Consequently, hepatitis A became a disease that was not only common but also vaccine-preventable.

# Pathophysiology
Hepatitis A is a liver disease caused by the hepatitis A virus (HAV). HAV has fecal-oral transmission and its infectivity peaks about 2-weeks before the onset of jaundice. Gross observation of the liver may show an enlarged and erythematous liver, while microscopically it may reveal lymphocyte infiltration and inflammation of the portal tracts.

# Causes
Hepatitis A is a liver disease caused by the hepatitis A virus (HAV). HAV has fecal-oral transmission and its infectivity peaks about 2-weeks before the onset of jaundice. Gross observation of the liver may show an enlarged and erythematous liver, while microscopically it may reveal lymphocyte infiltration and inflammation of the portal tracts.

# Differential Diagnosis
Hepatitis A must be differentiated from other diseases that cause fever, nausea, vomiting, jaundice, hepatomegaly, icteric sclera, elevated ALT, AST, and PCR such as other viral hepatitis, alcoholic hepatitis, and autoimmune hepatitis.

# Epidemiology and Demographics
The incidence of hepatitis A varies among eras, countries and even cities within the same country. In recent years it has been noted a shift in prevalence, what was once a disease more prevalent in children, is today predominant in adults.  In the United States, the incidence of hepatitis A in 2011 was 0.4 cases per 100,000 population. In recent years, the rates of hepatitis A have been similar among all age groups. After the introduction of the HAV vaccine, historic differences in rates of hepatitis A among racial/ethnic populations have also narrowed. In developed countries, elimination of historic geographic differences in incidence rates has also occurred. In developing countries with very poor sanitary conditions and hygienic practices, most children (90%) are infected with the hepatitis A virus before the age of 10.

# Risk Factors
Subjects who are not immunized against hepatitis A virus (HAV) and who travel to endemic areas where there is poor sanitation and lack of safe water are at increased risk of contracting HAV infection.  Additional risk factors for HAV include intravenous drug injection, living in a household with an infected person, having a sexual partner with acute HAV infection, and attending childcare centers.

# Screening
The detection of hepatitis A virus (HAV) antibodies in the blood is used to screen for hepatitis A. Anti-HAV IgG remains elevated after acute disease.

# Natural History, Complications and Prognosis
Hepatitis A is caused by infection with hepatitis A virus (HAV) which has an incubation period of approximately 28 days. HAV infection produces a self-limited disease, rarely leading to acute liver failure. The risk for symptomatic infection is related to the age of the patient.  While children most commonly have either asymptomatic or unrecognized infection, more than 80% of adults exhibit symptoms of acute viral hepatitis, such as fatigue, malaise, nausea, vomiting, and anorexia.  Possible complications of hepatitis A include dehydration, electrolyte imbalance, bleeding, and rarely fulminant hepatitis. The prognosis depends on the age of the patient and the underlying liver condition.  Approximately 10 to 15% of patients experience a relapse of symptoms during the 6 months following acute illness.

# Diagnosis

## History and Symptoms
Hepatitis A virus (HAV) infection can be either asymptomatic or symptomatic.  Symptoms of hepatitis A include fever, fatigue, loss of appetite, nausea, vomiting, abdominal pain, and jaundice.

## Physical Examination
Hepatitis A virus infection is commonly associated with fever, jaundice, icteric sclera, abdominal tenderness, and hepatomegaly on physical examination. Other pertinent findings include rash, cervical lymphadenopathy, abdominal distension, ascites, and altered mental status.

## Laboratory Findings
Hepatitis A cannot be differentiated from other types of viral hepatitis on the basis of clinical or epidemiologic features alone. Laboratory tests are required for its diagnosis. Serologic tests in hepatitis A virus (HAV) infection reveal elevated IgM anti-HAV in the acute phase (gold standard) in addition to an elevated IgG anti-HAV that remains elevated for the person's lifetime.  Additional laboratory findings include the detection and sequencing of HAV RNA, an elevated direct bilirubin, and elevated liver enzymes. Liver biopsy has a minimal role in the diagnosis of HAV infection and it is only used when the diagnosis is unclear or when relapse is suspected.

## CT
A CT scan is usually not indicated for the diagnosis of hepatitis A. However, it may be performed to exclude alternative diagnoses.

## Ultrasound
An ultrasound of the abdomen may be performed in patients with hepatitis A to rule out other possible causes of hepatomegaly or chronic liver disease. Common ultrasound findings in acute hepatitis A include brightness of the portal vein walls and decreased echogenicity of the liver.

# Treatment

## Medical Therapy
There is no specific treatment for hepatitis A. Recovery from symptoms following infection may be slow and may take several weeks or months. Therapy is aimed at maintaining comfort and adequate nutritional balance, including replacement of fluids that are lost from vomiting and diarrhea.

## Surgery
Patients who develop fulminant hepatitis may require aggressive supportive therapy, and be transferred to a center capable of performing liver transplantation.

## Primary Prevention
Two products are available for the prevention of HAV infection: hepatitis A vaccine and immune globulin (IG) for intramuscular (IM) administration.  Administered IM in a 2-dose series at 0 and 6--12 months, these vaccines induce protective antibody levels in virtually all adults. By 1 month after the first dose, 94%--100% of adults have protective antibody levels; 100% of adults develop protective antibody after a second dose. IG is a sterile solution of concentrated immunoglobulins which, when administered IM before or within 2 weeks after exposure to HAV, is >85% effective in preventing HAV infections.  Vaccination is the most effective means of preventing HAV transmission among persons at risk for infection (e.g., MSM, illegal drug users, and persons with chronic liver disease).  Because transmission of HAV during sexual activity probably results from fecal-oral contact, measures typically used to prevent the transmission of other sexually transmitted disease (e.g., use of condoms) do not prevent HAV transmission.

## Secondary Prevention
Until recently, an injection of immune globulin (IG) was the only recommended way to protect people after they have been exposed to hepatitis A virus. In June 2007, U.S. guidelines were revised to allow for hepatitis A vaccine to be used after exposure to prevent infection in healthy persons aged 140 years. Persons who recently have been exposed to hepatitis A virus (HAV) and who previously have not received hepatitis A vaccine should be administered a single dose of single-antigen vaccine or immunoglobulin (IG) (0.02 mL/kg) as soon as possible.  Information about the relative efficacy of vaccine compared with immunoglobulin postexposure is limited, and no data are available for persons aged more than 40 years or those with underlying medical conditions.  Therefore, decisions to use vaccine or immunoglobulin should take into account patient characteristics associated with more severe manifestations of hepatitis A, including older age and chronic liver disease.