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AIDS
Acquired Immune Deficiency
Syndrome (AIDS), a clinical syndrome (a group of
various illnesses that together characterize a
disease) resulting from damage to the immune
system caused by infection with the human
immunodeficiency virus (HIV).
AIDS VIRUS
The Human Immunodeficiency Virus (HIV),
which causes acquired immune deficiency syndrome
(AIDS), principally attacks T-4 lymphocytes, a
vital part of the human immune system. As a
result, the body’s ability to resist
opportunistic viral, bacterial, fungal,
protozoal, and other infection is greatly
weakened. Pneumocystis carinii pneumonia is the
leading cause of death among people with HIV
infection, but the incidence of certain types of
cancers such as B-cell lymphomas and Kaposi’s
sarcoma is also increased. Neurological
complications and dramatic weight loss, or
wasting, are characteristic of AIDS, which is
endstage HIV disease. HIV is transmitted
sexually; through contact with contaminated
blood, tissue, or needles; and from mother to
child during birth or breast-feeding. Full-blown
symptoms of AIDS may not develop for more than
10 years after infection.
In HIV-infected individuals, there is a gradual
loss of immune cells (called CD4+ T-lymphocytes)
and immune function. The mechanisms by which HIV
causes this immune deficiency are still not
completely understood, although direct infection
of CD4+ T-lymphocytes by HIV certainly plays a
role. The loss of immune function, if untreated,
results eventually in the development of
opportunistic diseases caused by common
infections that do not present a threat to
healthy individuals, including fungal,
bacterial, protozoal, and viral diseases, as
well as by malignancies that appear to be
associated with immune dysregulation. In the
absence of treatment, it generally takes six to
ten years from the point of infection to develop
AIDS, although the rate of disease progression
may vary substantially from person to person.
In the early 1980s deaths by opportunistic
infections, previously observed mainly in
transplant recipients receiving
immunosuppressive therapy, were recognized in
otherwise healthy homosexual men. In 1983, Luc
Montagnier and scientists at the Pasteur
Institute in Paris isolated what appeared to be
a new human retrovirus from the lymph node of a
man at risk of developing AIDS. Almost
simultaneously, both Robert Gallo’s group at the
National Cancer Institute (NCI), and a group
headed by Jay Levy at the University of
California, San Francisco, isolated a retrovirus
from AIDS patients and from people who had had
sexual contact with AIDS patients. All three
groups had isolated what is now known as HIV—the
aetiological (causative) agent of AIDS.
CAUSES OF TRANSMISSION
HIV can be transmitted by
either homosexual or heterosexual contact with
an infected person and these routes represent
the majority of transmissions. Present in the
sexual secretions of both men and women, HIV
gains access to the bloodstream of the
uninfected partner by infecting cells in mucous
membranes or via small abrasions that occur as a
consequence of intercourse. HIV is also spread
by sharing injecting equipment, most commonly
done by those abusing drugs, and this results in
a direct exposure to the blood from an infected
individual.
HIV transmission through medical transfusions or
blood-clotting factors is now extremely rare
because of extensive screening of the blood
supply. HIV can also be transmitted from an
infected mother (either before giving birth,
during labour, or through breastfeeding), but
only about 30 per cent of babies born to
untreated HIV-infected mothers are actually
infected, and the use of antiviral medications
by the mother and the newborn child can reduce
this risk almost to zero.
Although these routes of HIV transmission are
well established, public fear still exists
concerning the potential for transmission by
other means. There is no evidence that HIV can
be transmitted through the air or by biting
insects. If this were the case, the pattern of
HIV infections would be dramatically different
from what has been observed and cases of AIDS
would be reported more frequently in individuals
with no identifiable risk for infection (now
only a very small percentage of reported cases).
Although HIV is a very fragile virus and does
not survive well when exposed to the environment
(for example, drying of HIV-infected fluids
rapidly reduces their infectiousness almost to
zero), fear also exists for HIV transmission by
casual contact in a household, school,
workplace, or food-service setting. No
documented cases of HIV transmission by casual
contact with, or even kissing, an infected
individual have been identified. However,
practices that increase the likelihood of blood
contact, such as sharing toothbrushes or razors,
should be avoided.
Public fear has also persisted regarding HIV
transmission from infected health-care workers,
because of a case of transmission from a dentist
to several patients. This now appears to be an
extremely rare and isolated case of transmission
and, in general, infected health-care workers
pose no risk to their patients. There is no risk
of HIV transmission while donation Blood.
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