WORLD OF MICROBIOLOGY AND IMMUNOLOGY Hepatitis and hepatitis viruses265•
purification standards are poor, but also in developed, indus-
trialized nations, including the United States, where it
accounts for 30% of all incidences of clinical hepatitis. Except
in one to four percent of cases where sudden liver failure may
result in death, chronic liver disease and serious liver damage
very rarely develop, and “chronic carrier state,” in which
infected people with no visible symptoms harbor the virus and
transfer the disease to non-infected individuals, never occurs.
Also, reinfection seldom develops in recovered HAV patients
because the body eventually develops antibodies, cells which
provide a natural immunityto the specific virus attacking the
host. Although HAV is self-limiting (after time, ends as a
result of its own progress), there is as yet no effective treat-
ment once it is contracted.
Apart from the symptoms described above, HAV com-
monly produces a medium-grade fever, diarrhea, headaches,
and muscle pain. The primary route of HAV transmission is
fecal-oral through ingestion of water contaminated with raw
sewage, raw or undercooked shell-fish grown in contaminated
water, food contaminated by infected food handlers, and close
physical contact with an infected person. Heterosexual and
homosexual activities with multiple partners, travel from
countries with low incidences to countries with high rates of
infected population, and, less frequently, blood transfusions
and intravenous drug use also spread infection.
During the infectious stage, large numbers of viruses are
eliminated with the stool. Although HAV infection occurs in all
age groups, high rates of disease transmission occur in day-care
centers and nursery schools where children are not yet toilet
trained or able to wash their hands thoroughly after defecating.
The disease may then be transmitted to day-care workers and
carried home to parents and siblings. In areas of the world where
living quarters are extremely crowded and many people live in
unhygienic conditions, large outbreaks of HAV threaten people
of all ages. Because during the viruses’ incubation period—from
14 to 49 days—no symptoms are observable, and because symp-
toms seldom develop in young children, particularly those under
the age of two, the disease is often unknowingly but readily
transmitted before infected people can be isolated.
Avaccineagainst HAV is available. It appears to provide
good protection, if the first immunizationhas been received at
least four weeks prior to exposure. For adults, two immuniza-
tions about 6 months apart are recommended; for children,
three immunizations are necessary (two a month apart, and the
third six months later). High-risk groups who should receive
HAV vaccine include child care workers, military personnel,
Alaskan natives, frequent travelers to HAV endemic areas, lab-
oratory technicians where HAV is handled, people who work
with primates. The immunization lasts for 20 years.
If someone who is unimmunized is exposed to HAV, or
if a traveler cannot wait four weeks prior to departure for an
HAV endemic area, then immune globulin may be utilized to
avoid infection. Immune globulin is a naturally occurring sub-
stance harvested from the plasma in human blood, then
injected into an individual exposed to the HAV. Immune glob-
ulin prevents disease development in 80–90% of cases in clin-
ical trials. It also seems to be effective in reducing the number
of cases normally expected after outbreaks in schools andother institutions. As yet, the most effective control mecha-
nisms are public education regarding the importance of
improved personal hygiene, which in many instances is as
simple as washing hands thoroughly after using the toilet and
before handing food, and concerted worldwide efforts to
purify water supplies (including rivers and oceans) and
improve sanitation methods.
Acute HBV is currently the greatest cause of viral hep-
atitis throughout the world. World Health Organizationfigures
released in 1992 indicate that as many as 350 million people
worldwide carry the highly infectious HBV. Because of its
severity and often lengthy duration, 40% of those carriers—
possibly as many as two million per year—will eventually die
from resultant liver cancer or cirrhosis. HBV-related liver can-
cer deaths are second only to tobacco-related deaths world-
wide. Infected children who survive into adulthood may suffer
for years from the damage caused to the liver. In the United
States alone, as many as 300,000 people become infected with
HBV every year, medical costs amount to more than $1 mil-
lion per day, and the death rate over the last 15 or so years has
more than doubled in the United States and Canada.Vaccination against Hepatitis B virus.womi_H 5/6/03 3:20 PM Page 265