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Many viruses can infect the liver (Table 308-1). 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).
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Hepatitis is both a clinical and a laboratory diagnosis. The
best measure of liver injury is the enzyme alanine aminotransferase
(ALT), which is primarily released by hepatocytes during injury
or death. Inflammation of the liver can result from a variety of
causes. In the evaluation of a patient with hepatitis, it is also
necessary to consider nonviral diseases of the liver that can cause similar
symptoms (see Chapter 419). 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 (see Table 308-1). If just the transaminases are
mildly elevated, then waiting and repeating these test 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.
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HAV is a single-stranded ribonucleic acid (RNA) virus that is
classified as a picorna virus. First identified in the 1970s, it
is the major cause of infectious hepatitis. There are several genotypes
but only 1 known serotype. HAV causes acute hepatitis and asymptomatic
infection but never chronic infection.
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HAV is the most frequent cause of epidemic hepatitis in the United
States with rates highest in the western United States. Approximately 5000
to 10,000 cases are reported each year. This number represents only
10% of the estimated new cases. Approximately ...