AIDS - Description
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.
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
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
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.
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
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.
below). Early testing also alerts
HIV-infected people to avoid high-risk behaviors that could spread HIV to
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
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.
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
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
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.
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.
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:
1-800-243-7012 (TDD/Deaf Access)
For federally approved treatment guidelines on HIV/AIDS, call the HIV/AIDS
Treatment Information Service:
1-800-243-7012 (TDD/Deaf Access)