October 2003
HIV Infection and AIDS: An Overview
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.
HOW IS HIV TRANSMITTED?
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 sex.
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 AZT.
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
partners.
SYMPTOMS OF HIV INFECTION
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
- Fever
- Headache
- Tiredness
- 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
fluids.
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 include
- 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 treatment
- 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.
AIDS
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 other microbes.
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
- Fever
- Vision loss
- Nausea, abdominal cramps, and vomiting
- Weight loss and extreme fatigue
- Severe headaches
- Coma
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.
DIAGNOSIS
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 confidentiality.
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.
TREATMENT
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 antiretroviral drugs.
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 with AIDS.
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 infections
- 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 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 protein that occurs naturally in the human
body.
PREVENTION
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 getting HIV.
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.
RESEARCH
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.
MORE INFORMATION
AIDSinfo is a comprehensive information and referral service that provides
the most current information on federally and privately funded clinical
trials for AIDS patients and others infected with HIV. AIDS clinical trials
evaluate experimental drugs and other therapies for adults and children
at all stages of HIV infection -- from patients who are HIV positive with
no symptoms to those with various symptoms of AIDS.
As the main dissemination point for federally approved HIV treatment
and prevention guidelines, AIDSinfo provides information about the current
treatment regimens for HIV infection and AIDS-related illnesses, including
the prevention of HIV transmission from occupational exposure and mother-to-child
transmission during pregnancy. As an education and resource center,
AIDSinfo also offers links and other downloadable resources that are
designed for patients, health care providers, researchers and the general
public.
AIDSinfo is primarily web-based and can be found at http://aidsinfo.nih.gov.
AIDSinfo also operates a telephone service from 12:00 p.m. to 5:00 p.m.
Eastern Time, Monday through Friday. English and Spanish-speaking health
information specialists are available to answer questions about HIV/AIDS,
treatment options, and navigating the website.
Telephone: 800-HIV-0440 (1-800-448-0440)
International: 301-519-0459
TTY/TDD: 888-480-3739
Email: [email protected]
For information specifically about clinical trials conducted by the
NIAID Intramural AIDS Research Program, call 1-800-243-7644 (http://clinicaltrials.gov).
To receive materials or to talk with a Health Communication Specialist,
contact the CDC National HIV and STD Hotline. This service is available
24 hours a day.
1-800-2278922
1-800-342-2437
1-800-243-7889 (TTY/Deaf Access)
NIAID is a component of the National Institutes of Health
(NIH), which is an agency of the Department of Health and Human Services.
NIAID supports basic and applied research to prevent, diagnose, and
treat infectious and immune-mediated illnesses, including HIV/AIDS
and other sexually transmitted diseases, illness from potential agents
of bioterrorism, tuberculosis, malaria, autoimmune disorders, asthma
and allergies.
News releases, fact sheets and other NIAID-related
materials are available on the NIAID Web site at http://www.niaid.nih.gov.
Prepared by:
Office of Communications and Public Liaison
National Institute of Allergy and Infectious Diseases
National Institutes of Health
Bethesda, MD 20892
Last Updated November 21, 2003 (alt)
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