++
Many viruses can infect the liver (Table 303-1). Often, infection occurs as part of a disseminated viremia. In this chapter, we focus mainly on the 5 viruses whose primary target is the liver: the hepatitis viruses A through E (HAV, HBV, HCV, HDV, and HEV).
++++
Hepatitis is both a clinical and a laboratory diagnosis. Inflammation of the liver can result from a variety of causes. The most specific measure of liver injury is the enzyme alanine aminotransferase (ALT), which is primarily released by hepatocytes during injury or death. In the evaluation of a patient with hepatitis, it is also necessary to consider nonviral diseases of the liver (such as autoimmune, drug, congenital, bacterial, rickettsial, or fungal etiologies) that can cause similar symptoms. Because of the large number of potential viral causes of hepatitis, the evaluation of a patient can be confusing and complicated. The clinical context in which disease presents is the key to directing the workup (Table 303-1). If only the transaminases are mildly elevated, then waiting and repeating these tests might avoid an extensive and costly evaluation. Identifying the causative agent may not be critical for an asymptomatic transient elevation of transaminases. In symptomatic disease, it is impossible to establish the causative agent from symptoms alone.
++
HAV is a single-stranded ribonucleic acid (RNA) virus that is classified as a picornavirus. First identified in the 1970s, it is the major cause of infectious hepatitis worldwide. There are several genotypes but only 1 known serotype. HAV causes acute hepatitis and asymptomatic infection but never chronic infection.
++
HAV is the most frequent cause of epidemic hepatitis in the United States, with rates highest in the western ...