AIDS - acquired
immunodeficiency 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 damaging cells of
the body's immune system, HIV progressively destroys the body's ability to
fight infections and certain cancers. People diagnosed with AIDS may get
life-threatening diseases called opportunistic infections, which are
caused by microbes such as viruses or bacteria that usually do not make
healthy people sick.
More than 830,000 cases of AIDS have been reported in the United States
since 1981. As many as 950,000 Americans may be infected with HIV,
one-quarter of whom are unaware of their infection. The epidemic is
growing most rapidly among minority populations and is a leading killer of
African-American males ages 25 to 44. According to the U.S. Centers for
Disease Control and Prevention (CDC), AIDS affects nearly seven times more
African Americans and three times more Hispanics than whites.
HIV is spread most commonly by having
unprotected sex with an infected partner. The virus can enter the body
through the lining of the vagina, vulva, penis, rectum, or mouth during
HIV also is spread through contact with infected blood. Before donated
blood was screened for evidence of HIV infection and before heat-treating
techniques to destroy HIV in blood products were introduced, HIV was
transmitted through transfusions of contaminated blood or blood
components. Today, because of blood screening and heat treatment, the risk
of getting HIV from such transfusions is extremely small.
HIV frequently is spread among injection drug users by the sharing of
needles or syringes contaminated with very small quantities of blood from
someone infected with the virus. It is rare, however, for a patient to
give HIV to a health care worker or vice-versa by accidental sticks with
contaminated needles or other medical instruments.
Women can transmit HIV to their babies 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 mother takes the drug AZT during pregnancy, she can
significantly reduce the chances that her baby will get infected with HIV.
If health care providers treat mothers with AZT and deliver their babies
by cesarean section, the chances of the baby being infected can be reduced
to a rate of 1 percent.
A study sponsored by the National Institute of Allergy and Infectious
Diseases (NIAID) in Uganda found a highly effective and safe drug for
preventing transmission of HIV from an infected mother to her newborn.
This regimen is more affordable and practical than any other examined to
date. Results from the study show that a single oral dose of the
antiretroviral drug nevirapine (NVP) given to an HIV-infected woman in
labor and another to her baby within three days of birth reduces the
transmission rate of HIV by half compared with a similar short course of
Although researchers have found HIV in the saliva of infected people,
there is no evidence that the virus is spread by contact with saliva.
Laboratory studies reveal that saliva has natural properties that limit
the power of HIV to infect. Research studies of people infected with HIV
have found no evidence that the virus is spread to others through saliva
by kissing. No one knows, however, whether so-called "deep" kissing,
involving the exchange of large amounts of saliva, or oral intercourse
increase the risk of infection. 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 with an infected person without using a condom
- Having sexual contact with someone whose HIV status is unknown
Having a sexually transmitted disease such as syphilis, genital herpes,
chlamydial infection, gonorrhea, or bacterial vaginosis appears to make
people more susceptible to getting HIV infection during sex with infected
Many people do not have 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. This
illness may include
- Enlarged lymph nodes (glands 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. During this period, people
are very infectious, and HIV is present in large quantities in genital
More persistent or severe symptoms may not appear for 10 years 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
individual. Some people may begin to have symptoms within a few months,
while others may be symptom-free for more than 10 years.
Even during the asymptomatic period, the virus is actively multiplying,
infecting, and killing cells of the immune system. The most obvious effect
of HIV infection is a decline in the number of CD4 positive T cells (also
called T4 cells) found in the blood -- the immune system's key infection
fighters. At the beginning of its life in the human body, the virus
disables or destroys these cells without causing symptoms.
As the immune system worsens, a variety of complications start to take
over. For many people, the first signs of infection are 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
- 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 in women that does not respond to
- Short-term memory loss
Some people develop frequent and severe herpes infections that cause
mouth, genital, or anal sores, or a painful nerve disease called shingles.
Children may grow slowly or be sick a lot.
The term AIDS applies to the most advanced stages of HIV
infection. CDC developed official criteria for the definition of AIDS and
is responsible for tracking the spread of AIDS in the United States.
CDC's definition of AIDS includes all HIV-infected people who have
fewer than 200 CD4 positive T cells (abbreviated CD4+ T cells) per cubic
millimeter of blood (Healthy adults usually have CD4 positive T-cell
counts of 1,000 or more.). In addition, the definition includes 26
clinical conditions that affect people with advanced HIV disease. Most of
these conditions are opportunistic infections that generally do not affect
healthy people. In people with AIDS, 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, fungi, parasites, and
Symptoms of opportunistic infections common in people with AIDS include
- Coughing and shortness of breath
- Seizures and lack of coordination
- Difficult or painful swallowing
- Mental symptoms such as confusion and forgetfulness
- Severe and persistent diarrhea
- Vision loss
- Nausea, abdominal cramps, and vomiting
- Weight loss and extreme fatigue
- Severe headaches
Children with AIDS may get the same opportunistic infections as do
adults with the disease. In addition, they also have severe forms of the
bacterial infections all children may get, 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.
Signs 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 positive T cells; although some may have
abrupt and dramatic drops in their CD4 positive T-cell counts. A person
with CD4 positive T cells above 200 may experience some of the early
symptoms of HIV disease. Others may have no symptoms even though their CD4
positive T-cell count is below 200.
Many people are so debilitated by the symptoms of AIDS that they cannot
hold steady employment or do household chores. Other people with AIDS may
experience phases of intense life-threatening illness followed by phases
in which they function normally.
A small number of people first 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 genes 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 the disease from progressing.
Because early HIV infection often causes no symptoms, a
doctor or other health care provider usually can diagnose it by testing a
person's blood for the presence of antibodies (disease-fighting proteins)
to HIV. HIV antibodies generally do not reach detectable levels in the
blood for one to three months following infection. It may take the
antibodies as long as six months to be produced in quantities large enough
to show up in standard blood tests.
People exposed to the virus should get an HIV test as soon as they are
likely to develop antibodies to the virus - within 6 weeks to 12 months
after possible exposure to the virus. By getting tested early, people with
HIV infection can discuss with a health care provider when they should
start treatment to help their immune systems combat HIV and help prevent
the emergence of certain opportunistic infections (see section on
treatment below). Early testing also alerts HIV-infected people to avoid
high-risk behaviors that could spread the virus to others.
Most health care providers can do HIV testing and will usually offer
counseling to the patient at the same time. Of course, individuals can be
tested anonymously at many sites if they are concerned about
Health care providers diagnose HIV infection by using two different
types of antibody tests, ELISA and Western Blot. If a person is highly
likely to be infected with HIV and yet both tests are negative, the health
care provider may request additional tests. 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 doctor cannot make a definitive
diagnosis of HIV infection using standard antibody tests 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. Health
care experts are using new technologies to detect HIV itself to more
accurately determine HIV infection in infants between ages 3 months and 15
months. They are evaluating a number of blood tests to determine if they
can diagnose HIV infection in babies younger than 3 months.
When AIDS first surfaced in the United States, there
were no medicines to combat the underlying immune deficiency and few
treatments existed for the opportunistic diseases that resulted. During
the past 10 years, however, researchers have developed drugs to fight both
HIV infection and its associated infections and cancers.
The U.S. Food and Drug Administration (FDA) has approved a number of
drugs for treating HIV infection. The first group of drugs used to treat
HIV infection, called nucleoside reverse transcriptase (RT) inhibitors,
interrupts an early stage of the virus making copies of itself. Included
in this class of drugs (called nucleoside analogs) are AZT, ddC
(zalcitabine), ddI (dideoxyinosine), d4T (stavudine), 3TC (lamivudine),
abacavir (ziagen), and tenofovir (viread). These drugs may slow the spread
of HIV in the body and delay the start of opportunistic infections.
Health care providers can prescribe non-nucleoside reverse
transcriptase inhibitors (NNRTIs), such as delvaridine (Rescriptor),
nevirapine (Viramune), and efravirenz (Sustiva), in combination with other
FDA also has approved a second class of drugs for treating HIV
infection. These drugs, called protease inhibitors, interrupt virus
replication at a later step in its life cycle. They include
- Ritonavir (Norvir)
- Saquinivir (Invirase)
- Indinavir (Crixivan)
- Amprenivir (Agenerase)
- Nelfinavir (Viracept)
- Lopinavir (Kaletra)
Because HIV can become resistant to any of these drugs, health care
providers must use a combination treatment to effectively suppress the
virus. When RT inhibitors and protease inhibitors are used in combination,
it is referred to as highly active antiretroviral therapy, or HAART, and
can be used by people who are newly infected with HIV as well as people
Researchers have credited HAART as being a major factor in
significantly reducing the number of deaths from AIDS in this country.
While HAART is not a cure for AIDS, it has greatly improved the health of
many people with AIDS and it reduces the amount of virus circulating in
the blood to nearly undetectable levels. Researchers, however, have shown
that HIV remains present in hiding places, such as the lymph nodes, brain,
testes, and retina of the eye, even in patients who have been treated.
Despite the beneficial effects of HAART, there are side effects
associated with the use of antiviral drugs that can be severe. Some of the
nucleoside RT inhibitors may cause a decrease of red or white blood cells,
especially when taken in the later stages of the disease. Some may also
cause inflammation of the pancreas and painful nerve damage. There have
been reports of complications and other severe reactions, including death,
to some of the antiretroviral nucleoside analogs when used alone or in
combination. Therefore, health care experts recommend that people on
antiretroviral therapy be routinely seen and followed by their health care
providers. 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.
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 to treat cytomegalovirus (CMV)eye
- Fluconazole to treat yeast and other fungal infections
- Trimethoprim/sulfamethoxazole (TMP/SMX) or pentamidine to treat
Pneumocystis carinii pneumonia (PCP)
In addition to antiretroviral therapy, health care providers treat
adults with HIV, whose CD4+ T-cell counts drop below 200, to prevent the
occurrence of PCP, which is one of the most common and deadly
opportunistic infections associated with HIV. They give children 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 take
drugs for the rest of their lives to prevent a recurrence of the
HIV-infected individuals who develop Kaposi's sarcoma or other cancers
are treated with radiation, chemotherapy, or injections of alpha
interferon, a genetically engineered protein that occurs naturally in the
Because 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.
Many people infected with HIV have no symptoms. Therefore, there is no
way of knowing with certainty whether a sexual partner is infected unless
he or she has repeatedly tested negative for the virus and has not engaged
in any risky behavior.
People should either abstain from having sex or use male latex condoms
or female polyurethane condoms, which may offer partial protection, during
oral, anal, or vaginal sex. Only water-based lubricants should be used
with male latex condoms.
Although some laboratory evidence shows that spermicides can kill HIV,
researchers have not found that these products can prevent a person from
The risk of HIV transmission from a pregnant woman to her baby is
significantly reduced if she takes AZT during pregnancy, labor, and
delivery, and if her baby takes it for the first six weeks of life.
NIAID-supported investigators are conducting an abundance
of research on all areas of HIV infection, including developing and
testing preventive HIV vaccines and new treatments for HIV infection and
AIDS- associated opportunistic infections. Researchers also are
investigating exactly how HIV damages the immune system. This research is
identifying new and more effective targets for drugs and vaccines.
NIAID-supported investigators also continue to trace how the disease
progresses in different people.
Scientists are investigating and testing chemical barriers, such as
topical microbicides, that people can use in the vagina or in the rectum
during sex to prevent HIV transmission. They also are looking at other
ways to prevent transmission, such as controlling sexually transmitted
diseases and modifying people's behavior, as well as ways to prevent
transmission from mother to child.
Intramural AIDS Research Program
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