Microcheck 246

Rotaviruses are the leading cause of viral gastroenteritis in infants and children, and they also are a common cause of traveler's diarrhea. Norwalk viruses cause almost half the viral gastroenteritis in children and adults. Hepatitis A is transmitted by the fecal-oral route and is preventable by gamma globulin and an inactivated vaccine. Hepatitis B, transmitted by exposure to blood and by sexual intercourse, is preventable by a vaccine produced in yeast. A combination hepatitis A and hepatitis B vaccine is available. Hepatitis C is transmitted by blood and perhaps occasionally by sexual intercourse. Chronic hepatitis often results in cirrhosis and cancer.

■ What two serious complications can occur late in the course of both chronic hepatitis B and C?

■ Why might it be more difficult to prepare a vaccine against Norwalk viruses than rotaviruses?

■ At what stage in the replication of hepatitis B would a reverse transcriptase inhibitor act?

Table 24.12 Viral Hepatitis

Disease

Hepatitis A

Hepatitis B

Hepatitis C

Causative agent

Non-enveloped, single-stranded RNA picornavirus, HAV

Enveloped, double-stranded DNA hepadnavirus, HBV

Enveloped, single-stranded RNA flavivirus, HCV

Mode of spread

Fecal-oral

Blood, semen

Blood, possibly semen

Incubation period

3 to 5 weeks (range, 2 to 7 weeks)

10 to 15 weeks (range, 6 to 23 weeks)

6 to 7 weeks (range, 2 to 24 weeks)

Prevention

Gamma globulin; inactivated vaccine

Recombinant vaccine; imunoglobulin

No vaccine

Comments

Usually mild symptoms, but often prolonged; full recovery; no long-term carriers; combined hepatitis A and hepatitis B vaccine available

Symptoms often more severe than hepatitis A; progressive liver damage in 1% to 6% can lead to cirrhosis and cancer; chronic carriers; can cross the placenta; combined hepatitis A and hepatitis B vaccine available

Usually few or no symptoms; progressive liver damage or cancer in 10% to 20% of cases; chronic carriers; virus can cross the placenta (rare)

Disease

Hepatitis D

Hepatitis E

Hepatitis G

Causative agent

Defective single-stranded RNA virus, HDV

Non-enveloped, single-stranded RNA calcivirus, HEV

Single-stranded RNA flavivirus

Mode of spread

Blood, semen

Fecal-oral

Blood, possibly semen

Incubation period

2 to 12 weeks

2 to 6 weeks

Weeks

Prevention

No vaccine

No vaccine

No vaccine

Comments

Prior or concurrent HBV infection necessary; can cause worsening of hepatitis B; can cross the placenta

Similar to hepatitis A, except severe disease in pregnant women; same or related virus in rats

Usually mild symptoms; persistant viremia for months or years

24.7 Protozoan Diseases of the Lower Alimentary System

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