HIV
Infection and AIDS
AIDS –
acquired immune deficiency syndrome – was
first reported in the United States in 1981 and has since become
a major worldwide epidemic. AIDS is caused by the human immunodeficiency
virus (HIV). By killing or impairing cells of the immune system,
HIV progressively destroys the body's ability to fight infections
and certain cancers. Individuals diagnosed with AIDS are susceptible
to life-threatening diseases called opportunistic infections,
which are caused by microbes that usually do not cause illness
in healthy people.
More than 600,000
cases of AIDS have been reported in the United States since
1981, and as many as 900,000 Americans may be infected with
HIV. The epidemic is growing most rapidly among minority populations
and is a leading killer of African-American males. According
to the U.S. Centers for Disease Control and Prevention (CDC),
the prevalence of AIDS is six times higher in African-Americans
and three times higher among Hispanics than among whites.
Transmission
HIV is spread most
commonly by sexual contact with an infected partner. The virus
can enter the body through the lining of the vagina, vulva,
penis, rectum or mouth during sex.
HIV also is spread
through contact with infected blood. Prior to the screening
of blood for evidence of HIV infection and before the introduction
in 1985 of heat-treating techniques to destroy HIV in blood
products, HIV was transmitted through transfusions of contaminated
blood or blood components. Today, because of blood screening
and heat treatment, the risk of acquiring HIV from such transfusions
is extremely small.
HIV frequently
is spread among injection drug users by the sharing of needles
or syringes contaminated with minute quantities of blood of
someone infected with the virus. However, transmission from
patient to health-care worker or vice-versa via accidental
sticks with contaminated needles or other medical instruments
is rare.
Women can transmit
HIV to their fetuses during pregnancy or birth. Approximately
one-quarter to one-third of all untreated pregnant women infected
with HIV will pass the infection to their babies. HIV also
can be spread to babies through the breast milk of mothers
infected with the virus. If the drug AZT is taken during pregnancy,
the chance of transmitting HIV to the baby is reduced significantly.
If AZT treatment of mothers is combined with cesarean sectioning
to deliver infants, infection rates can be reduced to 1 percent.
Although researchers
have detected HIV in the saliva of infected individuals, no
evidence exists that the virus is spread by contact with saliva.
Laboratory studies reveal that saliva has natural compounds
that inhibit the infectiousness of HIV. Studies of people
infected with HIV have found no evidence that the virus is
spread to others through saliva such as by kissing. No one
knows, however, the risk of infection from so-called "deep"
kissing, involving the exchange of large amounts of saliva,
or by oral intercourse. Scientists also have found no evidence
that HIV is spread through sweat, tears, urine or feces.
Studies of families
of HIV-infected people have shown clearly that HIV is not
spread through casual contact such as the sharing of food
utensils, towels and bedding, swimming pools, telephones or
toilet seats. HIV is not spread by biting insects such as
mosquitoes or bedbugs.
HIV can infect
anyone who practices risky behaviors such as:
- sharing drug
needles or syringes;
- having sexual
contact without using a latex male condom with an infected
person or with someone whose HIV status is unknown.
Having another
sexually transmitted disease such as syphilis, herpes, chlamydial
infection, gonorrhea or bacterial vaginosis appears to make
someone more susceptible to acquiring HIV infection during
sex with an infected partner.
Early
Symptoms
Many people do
not develop any symptoms when they first become infected with
HIV. Some people, however, have a flu-like illness within
a month or two after exposure to the virus. They may have
fever, headache, malaise and enlarged lymph nodes (organs
of the immune system easily felt in the neck and groin). These
symptoms usually disappear within a week to a month and are
often mistaken for those of another viral infection. People
are very infectious during this period, and HIV is present
in large quantities in genital secretions.
More persistent
or severe symptoms may not surface for a decade or more after
HIV first enters the body in adults, or within two years in
children born with HIV infection. This period of "asymptomatic"
infection is highly variable. Some people may begin to have
symptoms in as soon as a few months, whereas others may be
symptom-free for more than 10 years. During the asymptomatic
period, however, HIV is actively multiplying, infecting and
killing cells of the immune system. HIV's effect is seen most
obviously in a decline in the blood levels of CD4+ T cells
(also called T4 cells) – the immune system's
key infection fighters. The virus initially disables or destroys
these cells without causing symptoms.
As the immune system
deteriorates, a variety of complications begins to surface.
One of the first such symptoms experienced by many people
infected with HIV is large lymph nodes or "swollen glands"
that may be enlarged for more than three months. Other symptoms
often experienced months to years before the onset of AIDS
include a lack of energy, weight loss, frequent fevers and
sweats, persistent or frequent yeast infections (oral or vaginal),
persistent skin rashes or flaky skin, pelvic inflammatory
disease that does not respond to treatment, or short-term
memory loss.
Some people develop
frequent and severe herpes infections that cause mouth, genital
or anal sores, or a painful nerve disease known as shingles.
Children may have delayed development or failure to thrive.
AIDS
The term AIDS applies
to the most advanced stages of HIV infection. Official criteria
for the definition of AIDS are developed by the CDC in Atlanta,
Ga., which is responsible for tracking the spread of AIDS
in the United States.
In 1993, CDC revised
its definition of AIDS to include all HIV-infected people
who have fewer than 200 CD4+ T cells. (Healthy adults usually
have CD4+ T-cell counts of 1,000 or more.) In addition, the
definition includes 26 clinical conditions that affect people
with advanced HIV disease. Most AIDS-defining conditions are
opportunistic infections, which rarely cause harm in healthy
individuals. In people with AIDS, however, these infections
are often severe and sometimes fatal because the immune system
is so ravaged by HIV that the body cannot fight off certain
bacteria, viruses and other microbes.
Opportunistic infections
common in people with AIDS cause such symptoms as coughing,
shortness of breath, seizures, mental symptoms such as confusion
and forgetfulness, severe and persistent diarrhea, fever,
vision loss, severe headaches, weight loss, extreme fatigue,
nausea, vomiting, lack of coordination, coma, abdominal cramps,
or difficult or painful swallowing.
Although children
with AIDS are susceptible to the same opportunistic infections
as adults with the disease, they also experience severe forms
of the bacterial infections to which children are especially
prone, such as conjunctivitis (pink eye), ear infections and
tonsillitis.
People with AIDS
are particularly prone to developing various cancers, especially
those caused by viruses such as Kaposi's sarcoma and cervical
cancer, or cancers of the immune system known as lymphomas.
These cancers are usually more aggressive and difficult to
treat in people with AIDS. Hallmarks of Kaposi's sarcoma in
light-skinned people are round brown, reddish or purple spots
that develop in the skin or in the mouth. In dark-skinned
people, the spots are more pigmented.
During the course
of HIV infection, most people experience a gradual decline
in the number of CD4+ T cells, although some individuals may
have abrupt and dramatic drops in their CD4+ T-cell counts.
A person with CD4+ T cells above 200 may experience some of
the early symptoms of HIV disease. Others may have no symptoms
even though their CD4+ T-cell count is below 200.
Many people are
so debilitated by the symptoms of AIDS that they are unable
to hold steady employment or do household chores. Other people
with AIDS may experience phases of intense life-threatening
illness followed by phases of normal functioning.
A small number
of people (less than 50) initially infected with HIV 10 or
more years ago have not developed symptoms of AIDS. Scientists
are trying to determine what factors may account for their
lack of progression to AIDS, such as particular characteristics
of their immune systems, or whether they were infected with
a less aggressive strain of the virus or if their genetic
make-up may protect them from the effects of HIV. Scientists
hope that understanding the body’s natural method of control
may lead to ideas for protective HIV vaccines and use of vaccines
to prevent disease progression.
Diagnosis
Because early HIV
infection often causes no symptoms, it is primarily detected
by testing a person's blood for the presence of antibodies
(disease-fighting proteins) to HIV. HIV antibodies generally
do not reach detectable levels until one to three months following
infection and may take as long as six months to be generated
in quantities large enough to show up in standard blood tests.
HIV testing may also be performed on saliva and urine samples,
in addition to blood samples.
People exposed
to HIV should be tested for HIV infection as soon as they
are likely to develop antibodies to the virus. Such early
testing will enable them to receive appropriate treatment
at a time when they are most able to combat HIV and prevent
the emergence of certain opportunistic infections (see Treatment below). Early testing also alerts
HIV-infected people to avoid high-risk behaviors that could
spread HIV to others.
HIV testing is
done in most doctors' offices or health clinics and should
be accompanied by counseling. Individuals can be tested anonymously
at many sites if they have particular concerns about confidentiality.
In addition, blood samples for anonymous HIV testing may now
be collected at home. Home-based test kits are available by
telephone order or over the counter at pharmacies.
Two different types
of antibody tests, ELISA and Western Blot, are used to diagnose
HIV infection. If a person is highly likely to be infected
with HIV and yet both tests are negative, a doctor may test
for the presence of HIV itself in the blood. The person also
may be told to repeat antibody testing at a later date, when
antibodies to HIV are more likely to have developed.
Babies born to
mothers infected with HIV may or may not be infected with
the virus, but all carry their mothers' antibodies to HIV
for several months. If these babies lack symptoms, a definitive
diagnosis of HIV infection using standard antibody tests cannot
be made until after 15 months of age. By then, babies are
unlikely to still carry their mothers' antibodies and will
have produced their own, if they are infected. New technologies
to detect HIV itself are being used to more accurately determine
HIV infection in infants between ages 3 months and 15 months.
A number of blood tests are being evaluated to determine if
they can diagnose HIV infection in babies younger than 3 months.
Treatment
When AIDS first
surfaced in the United States, no drugs were available to
combat the underlying immune deficiency and few treatments
existed for the opportunistic diseases that resulted. Over
the past 10 years, however, therapies have been developed
to fight both HIV infection and its associated infections
and cancers.
The Food and Drug
Administration has approved a number of drugs for the treatment
of HIV infection. The first group of drugs used to treat HIV
infection, called nucleoside analog reverse transcriptase
inhibitors (NRTIs), interrupt an early stage of virus replication.
Included in this class of drugs are zidovudine (also known
as AZT), zalcitabine (ddC), didanosine (ddI), stavudine (D4T),
lamivudine (3TC) and abacavir succinate. These drugs may slow
the spread of HIV in the body and delay the onset of opportunistic
infections. Importantly, they do not prevent transmission
of HIV to other individuals. Non-nucleoside reverse transcriptase
inhibitors (NNRTIs) such as delavirdine, nevirapine and efavirenz
are also available for use in combination with other antiretroviral
drugs.
A third class of
anti-HIV drugs, called protease inhibitors, interrupts virus
replication at a later step in its life cycle. They include
ritonavir, saquinivir, indinavir and nelfinavir. Because HIV
can become resistant to each class of drugs, combination treatment
using both is necessary to effectively suppress the virus.
Currently available
antiretroviral drugs do not cure people of HIV infection or
AIDS, however, and they all have side effects that can be
severe. AZT may cause a depletion of red or white blood cells,
especially when taken in the later stages of the disease.
If the loss of blood cells is severe, treatment with AZT must
be stopped. DdI can cause an inflammation of the pancreas
and painful nerve damage.
The most common
side effects associated with protease inhibitors include nausea,
diarrhea and other gastrointestinal symptoms. In addition,
protease inhibitors can interact with other drugs resulting
in serious side effects. Investigators also recently have
reported cases of abnormal redistribution of body fat among
some individuals receiving protease inhibitors.
A number of drugs
are available to help treat opportunistic infections to which
people with HIV are especially prone. These drugs include
foscarnet and ganciclovir, used to treat cytomegalovirus eye
infections, fluconazole to treat yeast and other fungal infections,
and TMP/SMX or pentamidine to treat Pneumocystis carinii
pneumonia (PCP).
In addition to
antiretroviral therapy, adults with HIV whose CD4+ T-cell
counts drop below 200 are given treatment to prevent the occurrence
of PCP, which is one of the most common and deadly opportunistic
infections associated with HIV. Children are given PCP preventive
therapy when their CD4+ T-cell counts drop to levels considered
below normal for their age group. Regardless of their CD4+
T-cell counts, HIV-infected children and adults who have survived
an episode of PCP are given drugs for the rest of their lives
to prevent a recurrence of the pneumonia.
HIV-infected individuals
who develop Kaposi's sarcoma or other cancers are treated
with radiation, chemotherapy or injections of alpha interferon,
a genetically engineered naturally occurring protein.
Prevention
Since no vaccine
for HIV is available, the only way to prevent infection by
the virus is to avoid behaviors that put a person at risk
of infection, such as sharing needles and having unprotected
sex.
Because many people
infected with HIV have no symptoms, there is no way of knowing
with certainty whether a sexual partner is infected unless
he or she has been repeatedly tested for the virus or has
not engaged in any risky behavior. CDC recommends that people
either abstain from sex or protect themselves by using male
latex condoms whenever having oral, anal or vaginal sex. Only
male condoms made of latex should be used, and water-based
lubricants should be used with latex condoms.
Although some laboratory
evidence shows that spermicides can kill HIV organisms, in
clinical trials, researchers have not found that these products
can prevent HIV.
The risk of HIV
transmission from a pregnant woman to her fetus is significantly
reduced if she takes AZT during pregnancy, labor and delivery,
and her baby takes it for the first six weeks of life.
Research
NIAID-supported
investigators are conducting an abundance of research on HIV
infection, including the development and testing of HIV vaccines
and new therapies for the disease and some of its associated
conditions. More than a dozen HIV vaccines are being tested
in people, and many drugs for HIV infection or AIDS-associated
opportunistic infections are either in development or being
tested. Researchers also are investigating exactly how HIV
damages the immune system. This research is suggesting new
and more effective targets for drugs and vaccines. NIAID-supported
investigators also continue to document how the disease progresses
in different people.
For information
about studies of new HIV therapies, call the AIDS Clinical
Trials Information Service:
1-800-TRIALS-A
1-800-243-7012 (TDD/Deaf Access)
For
federally approved treatment guidelines on HIV/AIDS, call
the HIV/AIDS Treatment Information Service:
1-800-HIV-0440
1-800-243-7012 (TDD/Deaf Access)
National Institutes of Health
March 1999
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