HIV Causes a Breakdown
of the Immune Response
LEARNING OBJECTIVES
1.
Distinguish
between HIv and AIDS.
2.
Describe
the structure and mechanism of action
of HIv.
3.
Outline
the symptoms and progression of AIDS.
4.
Identify
treatments for HIv infection.
cquired
immunodeficiency
syndrome
(AIDS) is a condition in which a person expe-
riences an assortment of infections due to the
progressive destruction of cells of the lym-
phatic system. The destruction is caused by a virus called
human immunodeficiency virus (HIV). Upon infection
with HIV, the affected individual may experience no symp-
toms for many years but then deteriorate rapidly into a
condition that is ultimately fatal. Since the first cases of
AIDS were reported in 1981, more than 20 million people
have died from the disease. Currently more than 40 mil-
lion people worldwide are infected with HIV
It Is Not Easy to Get Infected with HIV
HIV is present in the blood and body fluids of an infect-
ed person. The virus is transmitted from person to per-
son through the exchange of bodily fluids (for example,
blood, semen, vaginal fluid, breast milk). The most com-
mon routes of transmission include unprotected (without
a condom) sexual intercourse, anal intercourse, oral sex,
intravenous drug use that involves sharing of needles, and
accidental needle sticks from HIV-contaminated needles.
(The latter is most common among health care providers.)
HIV is fragile and does not survive long outside the body.
The virus cannot be spread through casual contact, such
as hugging or sharing household items, and it can be eas-
ily eliminated from items with heat (57.2°C for 10 min),
by disinfecting (using hydrogen peroxide, rubbing alco-
hol, bleach, or germicidal cleansers such as Betadine or
Hibiclens), or by standard dishwashing or clothes washing.
HIV cannot be transmitted through insect bites.
The Symptoms of HIV Infection
Progress in Severity
HIV is a
retro viru s
—a virus that can convert its RNA into
DNA
(retro-
= “backward”). This virus contains RNA
and some proteins necessary to incorporate its nucleic acid
into a host cell’s DNA in a process called
reverse tra n scription.
The virus can remain dormant for an extended period of
time, or it can force the host cell to make new particles of
the virus. The virus attacks mainly helper T cells and can
replicate more than 10 billion new viruses daily. Eventual-
ly, the host cell ruptures and dies, while new viruses infect
other cells. Initially, helper T cells reproduce almost as fast
as HIV destroys them, but after several years, the ability to
replace T cells diminishes and the T cell concentration in
the circulation gradually declines.
When the initial HIV infection occurs, the individual
experiences flu-like symptoms (Figure 12.13a). During
the initial infection, the virus spreads throughout the body.
The initial infection is followed by a latency period, during
which the T cell count is relatively stable but low ( Fig-
ure 12.13b). Once the T cell count drops, however, the
affected individual is unable to respond immunologically
to even simple infections. At this point, the HIV infection
has progressed to AIDS. The AIDS patient experiences
c o n stitu tio n a l sym ptom s
including persistent fatigue, weight
loss, enlarged lymph nodes, night sweats, rashes, diarrhea,
and various lesions (of the mouth, gums, and skin). Death
usually occurs due to one or more
op p o rtu n istic diseases
infec-
tions that the lymphatic system would have normally held
in check (such as pneumonia).
If left untreated, people with HIV infections often
begin showing symptoms of AIDS within 10 to 12 years.
Once AIDS develops, untreated patients usually die within
8 to 12 months. Although there is no cure for HIV infec-
tion, some pharmaceutical therapies have been developed
to prevent viral replication and help extend the lives of
HIV-infected people (12.13c). Reverse transcriptase in-
hibitors block the action of HIV’s reverse transcriptase
enzyme from making DNA copies of the viral RNA. Prote-
ase inhibitors block the actions of HIV’s protease, which
cuts host proteins into pieces to assemble the coat of new
HIV virus particles.
Highly active antiretroviral therapy (HAART) is
a combination of two different reverse transcriptase in-
hibitors and one protease inhibitor that is effective but
expensive (—$ 10,000 per year). In any patient, HAART
drastically reduces levels of HIV, increases helper T cell
counts, delays HIV progression to AIDS, and causes re-
mission, or disappearance of opportunistic infections, re-
storing some semblance of normal health. However, HIV
remains in the body and can be transmitted to others.
362 CHAPTER 12
The Lymphatic System and Immunity
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