The hepatitis A virus (HAV) is a common infectious etiology of acute hepatitis worldwide. HAV is most commonly transmitted through the oral-fecal route via exposure to contaminated food, water, or close physical contact with an infectious person. According to the World Health Organization (WHO), infection rates in developed countries are low. However, high-risk groups include injection-drug users, men who have sex with men, people traveling to endemic areas, and isolated communities. HAV does not cause chronic liver disease unlike hepatitis B or C. Acute hepatitis as an infection usually presents as a self-limited illness; development of fulminant hepatitis is rare. Typical symptoms of acute infection include nausea, vomiting, abdominal pain, fatigue, malaise, poor appetite, and fever; management is with supportive care. Alternate clinical patterns include cholestatic, prolonged, and relapsing disease. Vaccination against HAV is recommended for children 12 months or older and adults with the risk of exposure including travelers to endemic countries, men who have sex with men, illicit drug users, potential occupational exposure, and/or chronic liver disease.
HAV is one of the most common causes of acute hepatitis infection worldwide. The WHO estimates that approximately 1.5 million people are infected with HAV each year. Endemic rates are high in developing countries with low socioeconomic conditions and poor sanitation and hygiene practices. Exposure in these developing countries usually occurs in childhood. Infection rates are low in developed countries such as the United States, Canada, and Western Europe. High-risk groups in low endemicity countries have been identified as injection-drug users, men who have sex with men, people traveling to endemic areas, and isolated communities such as nursing homes and even day-care centers. The incidence of HAV in a given population correlates with socioeconomic properties such as income, the density of housing, sanitation, and water quality. With the implementation of vaccination, the incidence of HAV in the United States has significantly decreased. The incidence of acute HAV infection has decreased by 92% from 12 cases per 100,000 in 1995 to 1 case per 100,000 in 2007.
Improved sanitation has resulted in a shift in the age group that acquires hepatitis A. In recent years there has been a decline in the incidence of new infection.
The United States has a low endemicity. Mexico has a high prevalence of individuals with the anti-HAV antibody indicating a previous infection. The frequency of acute hepatitis is higher in those U.S. states that are adjacent to Mexico.
The reported hepatitis A incidence has declined by 90% to as low as 1.2 cases per 100,000 population. The greatest reductions are seen in children and in those states where routine vaccination was started in 1999. Over the last 4 decades, the average age of hepatitis A infected individuals has increased.
Individuals in high-risk populations account for most cases of HAV infection. These groups include foreign travelers to developing nations, gays, childcare workers, institutionalized individuals, and those living in poverty.
Food handlers are an infrequent source of outbreaks in the United States. Virtually any food may be contaminated with HAV.
HAV is highest in resource-poor regions such as Africa, Asia, and South America, where evidence of past infection is nearly universal. Acquisition often occurs in childhood, and it is usually asymptomatic.
There is no sexual predilection. It is most common in aid workers, gays, and around sewage.
With increasing age symptomatic disease and adverse sequelae increases. Mortality from fulminant hepatic failure increases with increasing age.
HAV, first identified in 1973 by Feinstone et al., is classified in the family Picornaviridae and genus Hepatovirus. It is a positive-sense, single-stranded RNA virus which replicates primarily within hepatocytes. Animal studies showing HAV antigen in the epithelial cells of intestinal crypts and cells of the lamina propria in the small intestine suggest replication might also occur at these sites. Once ingested orally, the virus is taken up from the gastrointestinal tract and the HAV particles are carried to the basolateral membrane of the hepatocyte via portal circulation. The hepatocellular injury in acute HAV infection is mediated by various immune mechanisms. It has been shown that patients with acute HAV infection have the virus-specific T-cell mediated release of cytotoxic interferon gamma. Additionally, recent mice-models have demonstrated HAV-induced hepatocellular apoptosis and inflammation associated with the innate immune response. The humoral immune response is responsible for the diagnostic serologic assays. Following replication in the liver, HAV is excreted in bile and released into the stool. The concentration of the virus is highest in the stool during the 2 weeks before onset of jaundice, at which point the individual is most infectious. Most people are no longer infectious 1 week after jaundice appears at which time stool shedding and viremia are decreased.
Acute HAV infection is typically a self-limited illness characterized by nausea, vomiting, right upper quadrant abdominal discomfort, malaise, anorexia, myalgia, fatigue, and fever. Patients may develop dark urine and pale stools within a week, followed by jaundice, icteric (yellow-tinted) sclera, and pruritus. Patients usually have elevated levels of serum alanine aminotransferase, aspartate aminotransferase, bilirubin, alkaline phosphatase, and lambda-glutamyl transpeptidase. These lab abnormalities typically resolve within 1 to 6 weeks following the onset of symptoms. The incubation period usually ranges from 14 to 28 days but can last up to 50 days. The severity of symptoms varies with age and comorbidities, particularly underlying chronic liver disease. Most children with acute HAV infection are asymptomatic.
Extra-hepatic manifestations rarely occur but may include pancreatitis, rash, acute kidney injury with interstitial nephritis or glomerular nephritis, pneumonitis, pericarditis, hemolysis, and acute cholecystitis. Neurologic complications have also been reported such as mononeuritis, Guillan-Barre, encephalitis and central myelitis. There were two reported cases in 1991 of autoimmune hepatitis triggered by acute HAV infection. Lemon et al. describe five clinical patterns:
Acute hepatitis A is diagnosed by serologic testing to detect HAV-specific immunoglobulin (IgM) antibodies in the blood. Additional testing can include reverse transcriptase polymerase chain reaction to detect the viral RNA. Immunoglobulin G (IgG) anti-HAV emerges soon after infection and remains present for the person’s lifetime.
No specific treatment is needed for most patients with acute, uncomplicated HAV infection beyond supportive care. Complete recovery from symptoms may take several weeks to months. In the rare case of fulminant hepatitis from HAV infection, liver transplantation may be a life-saving measure. Extrahepatic complications are managed routinely.
According to the WHO, the most effective way to prevent HAV infection is to improve sanitation, food safety, and immunization practices. In the United States, vaccination against hepatitis A is available as inactivated, single-antigen vaccines (HAVRIX and VAQTA) or in combination with hepatitis B (TWINRIX). The Centers for Disease Control and Prevention recommends vaccination for children 12 months or older, travelers to endemic countries, gays, illegal drug users, individuals with occupational risk exposure, persons with clotting factor disorders or chronic liver disease. Standard adult dosing recommends administration of two doses of the vaccine 6 to 12 months apart. These vaccines are highly efficacious were seroconversion rates approaching 100%.
Until more recently, immunoglobulin was the only treatment for post-exposure prophylaxis again HAV. However, animal studies and clinical trials demonstrated the efficacy of post-exposure immunization with an inactivated HAV vaccine has led the CDC to recommend the vaccine instead of immunoglobulin for exposure to HAV in healthy individuals aged 1 to 40 years. For individuals 41 years and older, immunoglobulin administration is preferred due to the risk of more severe clinical presentation and limited evidence of vaccine efficacy in this age group. Children less than 12 months, individuals with chronic liver disease, and immunocompromised persons should also receive immunoglobulin.