172 Chapter 9but most are the result of sexual contact with infected men.
In recent years, more young adults in the united states have
died from aIds than from any other single cause.hiv infection begins a fateful struggle
hIV is a retrovirus, which means that its primary genetic
instructions are in the form of rna, not dna. after hIV
infects a person, virus particles enter the bloodstream.
at this stage, many people have flulike symptoms as the
adaptive immune response begins. B cells make antibodies
that can be detected by an hIV test. armies of helper t cells
and killer t cells also form. With time, however, the adaptive
immune response begins to slow as up to 1 billion new virus
particles are built every day.
Over time, billions of hIV particles and masses of
infected t cells accumulate in lymph nodes. the number
of circulating virus particles also increases and the body
produces fewer and fewer helper t cells to replace those it
has lost. as the number of healthy helper t cells drops, the
person may lose weight and experience symptoms such as
fatigue, nausea, heavy night sweats, enlarged lymph nodes,
and a series of minor infections. With time, one or more of
the typical aIds indicator diseases appear (Figure 9.20B).
these are the diseases that eventually kill aIds patients.What are our anti-hiv weapons?
researchers have developed a fairly effective arsenal of
anti-hIV drugs. protease inhibitors block the action of hIV
protease, an enzyme required for the assembly of new virus
particles. Other drugs inhibit an enzyme that allows the
virus to reproduce itself.
at present the preferred treatment is antiretroviral
therapy, or art. patients receive a drug “cocktail” that
often consists of a protease inhibitor and at least two anti-
hIV drugs. this regimen can sometimes suppress hIV for
years. the World health Organization credits the increasing
availability of art for much of the recent decline in aIds
deaths. the drug cocktails may have serious side effects,
however, and because they are expensive, patients in
wealthier countries have easiest access to them.
the search also is on for compounds that might prevent
hIV from entering human cells. such “entry inhibitors” are
now being tested.
making an effective hIV vaccine has proven to be a tall
order. Because hIV mutates rapidly, there may be many
different genetic forms in a single person, and each presents
the immune system with a different antigen. no single
vaccine has yet been devised that can keep up with this
challenge. despite the obstacles, researchers are hopeful.
education programs around the world are having an
effect on the spread of the virus. In many—but not all—
countries, the incidence of new cases of hIV each year is
slowing. even so, many battles remain before we come
close to winning the global battle against aIds.AIDS (acquired immune deficiency syndrome) is a group of
diseases caused by infection with HIV, the human immune
deficiency virus. hIV infects and kills macrophages, dendritic
cells, and helper t cells. It leaves the body vulnerable to
infections and rare forms of cancer.
there is no way to rid the body of the known forms of
the virus. sooner or later, people who are infected begin to
develop symptoms of illness. diagnostic signs of aIds include
a severely depressed immune system, a positive hIV test,
and an “indicator disease,” including types of pneumonia,
recurrent yeast infections, cancer, and drug-resistant
tuberculosis. according to the World health Organization, in
2010 nearly 34 million people were living with hIV/aIds.hiv is transmitted in body fluids
hIV is transmitted when body fluids, especially blood and
semen, of an infected person enter another person’s tissues.
the virus can enter through any kind of cut or abrasion,
anywhere on or in the body. hIV-infected blood also can
be present on toothbrushes and razors; on needles used
to inject drugs, pierce ears, or do acupuncture; and on
contaminated medical equipment.
the most common mode of transmission is sex with
an infected partner. hIV in semen and vaginal secretions
enters a partner’s body through epithelium lining the penis,
vagina, rectum, or (rarely) mouth. anything that damages
the linings, such as other sexually transmitted diseases, anal
intercourse, or rough sex, increases the odds that the virus
will be transmitted.
hIV is not effectively transmitted by food, air, water,
casual contact, or insect bites. however, infected mothers
can transmit hIV to their babies during pregnancy, birth,
and breast-feeding (Figure 9.20a).
about half of hIV-infected adults worldwide are women.
some of those infections are due to intravenous drug abuse,Figure 9.20 HIV disables the immune system. A This Romanian
baby contracted AIDS from his mother’s breast milk and later
died. B Lesions of Kaposi’s sarcoma, a common cancer in adult
AIDS patients.A
A: © Peter Turnley/Corbis;B: © Zeva Oelbaum/PeterArnold, Inc.hiv and aiDs
9.10
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