Acquired Immune Deficiency Syndrome (AIDS), suppresses the immune
system related to infection with the human immunodeficiency virus (HIV). A person
infected with HIV gradually loses immune function along with certain immune cells
called CD4 T-lymphocytes or CD4 T-cells, causing the infected person to become
vulnerable to pneumonia, fungus infections, and other common ailments. With the loss
of immune function, a clinical syndrome (a group of various illnesses that together
characterize a disease) develops over time and eventually results in death due to
opportunistic infections (infections by organisms that do not normally cause disease
except in people whose immune systems have been greatly weakened) or cancers.
In the early 1980s deaths by opportunistic infections, previously observed
mainly in organ transplant recipients receiving therapy to suppress their immune
responses, were recognized in otherwise healthy homosexual men. In 1983, French
cancer specialist Luc Montagnier and scientists at the Pasteur Institute in Paris isolated
what appeared to be a new human retrovirus—a special type of virus that reproduces
differently from other viruses—from the lymph node of a man at risk for AIDS. Nearly
simultaneously, scientists working in the laboratory of
American research scientist Robert Gallo at the National Cancer Institute in Bethesda,
Maryland, and a group headed by American virologist Jay Levy at the University of
California at San Francisco isolated a retrovirus from people with AIDS and
individuals having contact with people with AIDS. All three groups of scientists
isolated what is now known as human immunodeficiency virus (HIV), the virus that
causes AIDS.
Infection with HIV does not necessarily mean that a person has AIDS, although
people who are HIV-positive are often mistakenly said to have AIDS. In fact, a person
can remain HIV-positive for more than ten years without developing any of the clinical
illnesses that define and constitute a diagnosis of AIDS. In 1996 an estimated 22.6
million people worldwide were living with HIV or AIDS—21.8 million adults and 830,000 children. The World Health Organization (WHO) estimates that between 1981, when the first AIDS cases were reported, and the end of 1996, more than 8.4 million adults and children had developed AIDS. In this same period there were 6.4 million deaths worldwide from AIDS or HIV. About 360,000 of these deaths occurred in the United States.
Clinical Progression of AIDS
The progression from the point of HIV infection to the clinical diseases that
define AIDS may take six to ten years or more. This progression can be monitored
using surrogate markers (laboratory data that correspond to the various stages of
disease progression) or clinical endpoints (illnesses associated with more advanced
disease). Surrogate markers for the various stages of HIV infection include the
declining number of CD4 T-cells, (the major type of white blood cell lost because of
HIV infection). In general, the lower the infected person’s CD4 T-cell count, the
weaker the person’s immune system and the more advanced the disease state. In 1996, it
became evident that the actual amount of HIV in a person’s blood—the so-called viral
burden—could be used to predict the progression to Aids, regardless of a person’s
CD4 T-cell count. With advancing technology, Viral Burden Determinations are
quickly becoming a standard means of patient testing. An infected person’s immune
response to the virus—that is, the person’s ability to produce antibodies against HIV—
can also be used to determine the progression ofAids; however, this surrogate marker is less precise during more advanced stages of
AIDS because of the overall loss of immune function.
Within one to three weeks after infection with HIV, most people experience
nonspecific flulike symptoms such as fever, headache, skin rash, tender lymph nodes,
and a vague feeling of discomfort. These symptoms last about one to two weeks.
During this phase, known as the acute retroviral syndrome phase, HIV reproduces to
very high concentrations in the blood, mutates (changes its genetic nature) frequently,
circulates through the blood, and establishes infections throughout the body, especially
in the lymphoid organs. The infected person’s CD4 T-cell count falls briefly but then
returns to near normal levels as the person’s immune system responds to the infection.
Individuals are thought to be highly infectious during this phase.
Following the acute retroviral syndrome phase, infected individuals enter a
prolonged asymptomatic phase—a symptom-free phase that can last ten years or more.
Persons with HIV remain in good health during this