Hepatitis and hepatitis viruses WORLD OF MICROBIOLOGY AND IMMUNOLOGY266•
If serology(blood) tests detect the presence of HBV six
months or more from time of initial diagnosis, the virus is then
termed “chronic.” Chronic persistent hepatitis may develop
following a severe episode of acute HBV. Within a year or
two, however, this type usually runs its course and the patient
recovers without serious liver damage. Chronic active hepati-
tis also may follow a severe attack of acute HBV infection, or
it may simply develop almost unnoticed. Unlike persistent
hepatitis, the chronic active type usually continues until fatal
liver damage occurs. In long-term studies of 17 patients with
chronic active hepatitis, 70% developed cirrhosis of the liver
within two to five years.
Symptoms are similar to those manifested by HAV and
may include weight loss, muscle aches, headaches, flu-like
symptoms, mild temperature elevation, and constipation or diar-
rhea. By the time jaundice appears, the patient may feel some-
what better overall but the urine becomes dark, stools light or
yellowish, the liver and possibly the spleen enlarged and
painful, and fluid may accumulate around the abdominal area.
Early in the disease’s life, however, symptoms may be very
slight or even virtually nonexistent, particularly in children,
facilitating infection of others before isolation is implemented.
The incubation period for HBV varies widely—any-
where from four weeks to six months. Primary routes of trans-
mission are blood or blood product transfusion; body fluids
such as semen, blood, and saliva (including a bite by an
infected human) organ and/or tissue transplants; contaminated
needles and syringes in hospitals or clinical settings; contami-
nated needles or syringes in illegal intravenous drug use; and
vertical transmission—from mother to baby during pregnancy,
birth, or after birth through breast milk. Even though they may
not develop symptoms of the disease during childhood, and
will remain healthy, almost all infected newborns become
chronic carriers, capable of spreading the disease. Many of
these infected yet apparently healthy children, particularly the
males, will develop cirrhosis and liver cancer in adulthood.
Where the incidence of the disease is relatively low, the pri-
mary mode of transmission appears to be sexual and strongly
related to multiple sex partners, particularly in homosexual
men. In locations where disease prevalence is high, the most
common form of transmission is from mother to infant.
Controlling HBV infection is an overwhelming task. In
spite of the development of safe and effective vaccines capa-
ble of preventing HBV in uninfected individuals, and regard-
less of programs designed to vaccinate adults in high-risk
categories such as male homosexuals, prostitutes, intravenous
drug users, health-care workers, and families of people known
to be carriers, the disease still remains relatively unchecked,
particularly in developing countries.
Although effective vaccines have been available since
the mid-1980s, the cost of mass immunization world-wide,
and particularly in developing countries, was initially prohib-
itive, while immunizing high-risk adult populations did little
to halt the spread of infection. Authorities now believe the
most effective disease control method will be immunization of
all babies within the first weeks following birth. Concerted
efforts of researchers and health authorities worldwide,
including the foundation in 1986 of an International TaskForce for Hepatitis B Immunization are investigating various
avenues for providing cost-effective, mass vaccinationpro-
grams. These include incorporating HBV vaccination into the
existing Expanded Program of Immunization controlled by the
World Health Organization. Methods of cost containment,
storing the vaccine, and distribution to midwives in remote
villages (60% of the world’s births occur at home), have been
designed and are continually being refined to ultimately attain
the goal of universal infant immunization. This will not only
drastically decrease the number of babies infected through
vertical transmission (which constitutes 40% of all HBV trans-
mission in Asia), preventing them from becoming adult carri-
ers, it also provides immunity throughout adulthood.
Finding an effective treatment for those infected with
HBV presents a major challenge to researchers—a challenge
equal to that posed by any other disease which still remains
unconquered. And HBV may present yet another challenge:
mutant forms of the virus seem to be developing in resistance
to the current vaccines, thus finding a way to survive, replicate
and continue its devastating course. Necessary measures in
disease control include: education programs aimed at health
care workers to prevent accidental HBV transfer—from an
infected patient to an uninfected patient, or to themselves;
strict controls over testing of blood, blood products, organs,
and tissue prior to transfusion or transplantation; and the “pas-
sive” immunization with immunoglobulin containing HBV
antibodies as soon as possible after exposure to the active
virus. Treatment with Interferon and new drug, Lamivudine,
have shown positive results in managing HBV.
Relatively recently discovered hepatitis viruses, often
called non-A, non-B hepatitis, exist in more than 100 million
carriers worldwide, with 175,000 new cases developing each
year in the U.S. and Europe.
Not until 1990 were serology tests available to identify
the hepatitis C virus (HCV). Research since then has deter-
mined that HCV is distributed globally and, like HBV, is impli-
cated in both acute and chronic hepatitis, as well as liver cancer
and cirrhosis. Eighty-five percent of all transfusion-related
hepatitis is caused by HCV, and mother-baby and sexual trans-
mission are also thought to spread the disease. Symptoms are
similar but usually less severe than HBV; however, it results in
higher rates of chronic infection and liver disease.
Control and prevention of HCV is a serious problem.
First, infected people may show no overt symptoms and the
likelihood that infection will become chronic means that many
unsuspecting carriers will transmit the disease. Second, HCV
infection does not appear to stimulate the development of anti-
bodies, which not only means infected people often become
reinfected, it creates a major challenge in the development of
an effective vaccine. Third, HCV exists in the same general
high-risk populations as does HBV. Combined, these factors
make reducing the spread of infection extremely difficult. On
a positive note, the development of accurate blood screening
for HCV has almost completely eliminated transfusion-related
spread of hepatitis in developed countries. Immunoglobulin
injections do not protect people who have been exposed to
HCV; the search is on for an adequate immunization, although
this effort is hampered by characteristics of HCV, whichwomi_H 5/6/03 3:20 PM Page 266