GASTROINTESTINAL DISORDERS - Medicine for Mountaineering and Other Wilderness Activities - page 273

Hepatitis B is caused by a DNA virus that is spread principally by body fluids through
personal contact, particularly sexual contact. As with hepatitis A, most individuals do not
realize they have an infection, but up to 10 percent may be quite ill, a few die, and approx-
imately 5 percent develop chronic liver disease. Approximately half the individuals with
chronic liver disease develop cirrhosis (scarring of the liver), an eventually lethal disorder.
Hepatitis B is directly responsible for many cases of hepatocellular carcinoma (a malig-
nancy arising in the liver), the most common malignant tumor on a worldwide basis, al-
thoughitisrelativelyuncommonintheUnitedStates.Asafeandeffectivevaccineforhep-
atitis B is available. Everyone should be vaccinated, but it is essential for medical workers,
others who come in contact with blood, and travelers to developing countries ( Chapter 5:
Immunizations ) .
The delta agent, or hepatitis D, is an incomplete DNA virus that can produce infections
only in association with hepatitis B. Therefore, immunization for hepatitis B prevents hep-
atitis D. Hepatitis D may be acquired simultaneously with hepatitis B or subsequently. In-
dividuals with both infections simultaneously have a higher risk of more severe disease.
AcutehepatitisBinfectionmaybecomerapidlyfatal,andchronichepatitisBismorelikely
to progress to cirrhosis when associated with hepatitis D infection.
Many of the infections previously termed non-A, non-B hepatitis are now known to be
caused by hepatitis C, a viral agent identified in 1989 that accounts for roughly 20 percent
of the cases of acute hepatitis and a much higher percentage of chronic, long-standing in-
fections in the United States. Acute infections are often asymptomatic and undiagnosed.
Greaterthan50percentofhepatitisCinfectionsresultinchronicliverdisease,whichisof-
ten asymptomatic but may cause persistent fatigue. Approximately 25 percent of individu-
als with chronic hepatitis C develop cirrhosis, an ultimately lethal disorder, within twenty-
five years of acquiring the infection. After twenty years, up to 5 percent of individuals, of-
ten with cirrhosis, develop hepatocellular carcinoma. Significant alcohol consumption in-
creases the risk of such severe complications.
For hepatitis following blood transfusion, 90 to 95 percent has been caused by hepatitis
C, although procedures for screening for this infection introduced in the early 1990s have
essentiallyeliminatedthisproblemintheUnitedStates.Indevelopingnationssuchscreen-
ing procedures often are not available or not affordable, and the risk of hepatitis C is much
higher. Hepatitis C is also spread in developing nations by needles and syringes that are
reused after being washed but not sterilized.
Hepatitis C is an RNA virus that is transmitted through broken skin or mucous mem-
branes mainly by blood-to-blood contact. Prior intravenous drug use accounts for 50 per-
centoftheinfections,sexualcontactfor10percent,bloodtransfusion(mostlybefore1993)
for 5 to 10 percent, and exposure to infected blood by nurses, ambulance attendants, and
similar medical professionals for 5 percent. The routes of inoculation for the remaining
one-thirdoftheinfectionsareunidentified,althoughhomemadetattoosandsharingcocaine