Acute viral hepatitis is a systemic infection with predominant hepatic involvement and remains a significant cause of morbidity and mortality in the United States despite the availability of effective vaccines against the two major causes of acute viral hepatitis, namely A and B. There are five major hepatotropic viruses (A, B, C, D, and E) that cause acute hepatitis with acute hepatic inflammation and necrosis. Acute viral hepatitis typically runs its course in 6 months or less, in contrast to chronic hepatitis, which persists for longer. However, with modern serologic and molecular diagnostic testing, the time course is less important in distinguishing acute from chronic viral hepatitis. The clinical illness produced by these viruses can range from asymptomatic or clinically inapparent to a fulminant and fatal acute infection. A major distinction between hepatitis A and hepatitis B, C, D, and E is that the former causes acute hepatitis only, in contrast to the latter four which cause acute and chronic hepatitis. Other viral infections, such as herpes simplex, Epstein–Barr virus (EBV), cytomegalovirus (CMV), and parvovirus B19, can present with prominent hepatic dysfunction, although they are usually multisystem disorders. Hepatitis G, human herpesviruses, adenovirus, coronavirus, and TT virus (TTV) have also been implicated in causing hepatic dysfunction, but their clinical significance remains dubious.
Hepatitis A virus
The hepatitis A virus (HAV) is an RNA virus, identified in 1973, transmitted via the fecal–oral route and is a common cause of acute viral hepatitis in North America. Community outbreaks due to contaminated water or food are well recognized. Inhabitants in low-socioeconomic areas, international travelers, intravenous drug users, and homosexual men are at particular risk of HAV infection. In the United States, the incidence has decreased remarkably since the introduction (1995) of HAV vaccination and its administration to all children as part of the universal childhood vaccination policy since 2006. In underdeveloped countries, HAV infection typically occurs in childhood and is subclinical (age ≤6 years, 70% are asymptomatic), with most of the population infected before adulthood acquiring life-long immunity. HAV infection occurring in older children and adults is more likely to be symptomatic, with increased morbidity and even mortality (Figure 43.1).