Реферат: Aids Essay Research Paper AidsAcquired Immune Deficiency

Aids Essay, Research Paper


Acquired Immune Deficiency Syndrome (AIDS), suppresses the immune

system related to infection with the human immunodeficiency virus (HIV). A person

infected with HIV gradually loses immune function along with certain immune cells

called CD4 T-lymphocytes or CD4 T-cells, causing the infected person to become

vulnerable to pneumonia, fungus infections, and other common ailments. With the loss

of immune function, a clinical syndrome (a group of various illnesses that together

characterize a disease) develops over time and eventually results in death due to

opportunistic infections (infections by organisms that do not normally cause disease

except in people whose immune systems have been greatly weakened) or cancers.

In the early 1980s deaths by opportunistic infections, previously observed

mainly in organ transplant recipients receiving therapy to suppress their immune

responses, were recognized in otherwise healthy homosexual men. In 1983, French

cancer specialist Luc Montagnier and scientists at the Pasteur Institute in Paris isolated

what appeared to be a new human retrovirus?a special type of virus that reproduces

differently from other viruses?from the lymph node of a man at risk for AIDS. Nearly

simultaneously, scientists working in the laboratory of

American research scientist Robert Gallo at the National Cancer Institute in Bethesda,

Maryland, and a group headed by American virologist Jay Levy at the University of

California at San Francisco isolated a retrovirus from people with AIDS and

individuals having contact with people with AIDS. All three groups of scientists

isolated what is now known as human immunodeficiency virus (HIV), the virus that

causes AIDS.

Infection with HIV does not necessarily mean that a person has AIDS, although

people who are HIV-positive are often mistakenly said to have AIDS. In fact, a person

can remain HIV-positive for more than ten years without developing any of the clinical

illnesses that define and constitute a diagnosis of AIDS. In 1996 an estimated 22.6

million people worldwide were living with HIV or AIDS?21.8 million adults and 830,000 children. The World Health Organization (WHO) estimates that between 1981, when the first AIDS cases were reported, and the end of 1996, more than 8.4 million adults and children had developed AIDS. In this same period there were 6.4 million deaths worldwide from AIDS or HIV. About 360,000 of these deaths occurred in the United States.

Clinical Progression of AIDS

The progression from the point of HIV infection to the clinical diseases that

define AIDS may take six to ten years or more. This progression can be monitored

using surrogate markers (laboratory data that correspond to the various stages of

disease progression) or clinical endpoints (illnesses associated with more advanced

disease). Surrogate markers for the various stages of HIV infection include the

declining number of CD4 T-cells, (the major type of white blood cell lost because of

HIV infection). In general, the lower the infected person?s CD4 T-cell count, the

weaker the person?s immune system and the more advanced the disease state. In 1996, it

became evident that the actual amount of HIV in a person?s blood?the so-called viral

burden?could be used to predict the progression to Aids, regardless of a person?s

CD4 T-cell count. With advancing technology, Viral Burden Determinations are

quickly becoming a standard means of patient testing. An infected person?s immune

response to the virus?that is, the person?s ability to produce antibodies against HIV?

can also be used to determine the progression ofAids; however, this surrogate marker is less precise during more advanced stages of

AIDS because of the overall loss of immune function.

Within one to three weeks after infection with HIV, most people experience

nonspecific flulike symptoms such as fever, headache, skin rash, tender lymph nodes,

and a vague feeling of discomfort. These symptoms last about one to two weeks.

During this phase, known as the acute retroviral syndrome phase, HIV reproduces to

very high concentrations in the blood, mutates (changes its genetic nature) frequently,

circulates through the blood, and establishes infections throughout the body, especially

in the lymphoid organs. The infected person?s CD4 T-cell count falls briefly but then

returns to near normal levels as the person?s immune system responds to the infection.

Individuals are thought to be highly infectious during this phase.

Following the acute retroviral syndrome phase, infected individuals enter a

prolonged asymptomatic phase?a symptom-free phase that can last ten years or more.

Persons with HIV remain in good health during this period, with levels of CD4 T-cells

ranging from low to normal (500 to 750 cells per cubic mm of blood). Nevertheless,

HIV continues to replicate during the asymptomatic phase, causing progressive

destruction of the immune system. Eventually, the immune system weakens to the point

that the person enters the early symptomatic phase. This phase can last from a few

months to several years and is characterized by rapidly falling levels of CD4 T-cells

(500 to 200 cells per cubic mm of blood) and opportunistic infections that are not life

threatening. Following the early symptomatic phase, the infected person experiences the

extensive immune destruction and serious illness that characterize the late symptomatic

phase. This phase can also last from a few months to years, and the affected individual

may have CD4 T-cell levels below 200 per cubic mm of blood along with certain

opportunistic infections that define AIDS. A wasting syndrome of progressive weight

loss and debilitating fatigue occurs in a large proportion of people in this stage. The

immune system is in a state of severe failure. The person eventually enters the

advanced AIDS phase, in which CD4 T-cell numbers are below 50 per cubic mm of

blood. Death due to severe life-threatening opportunistic infections and cancers usually

occurs within one to two years.

Opportunistic Illnesses

Death from AIDS is generally due not to HIV infection itself, but to

opportunistic infections that occur when the immune system can no longer protect the

body against agents normally found in the environment. The appearance of any one of

more than 25 different opportunistic infections, called AIDS-defining illnesses, along

with a CD4 T-cell count of less than 200 cells per cubic millimeter of blood provides

the clinical diagnosis of AIDS in HIV-infected individuals.

The most common opportunistic infection seen in AIDS is Pneumocystis Carinii

Pneumonia (PCP), which is caused by a fungus that normally exists in the airways of all

people. Bacterial Pneumonia and Tuberculosis are also commonly associated with

AIDS. In the late symptomatic phase of AIDS, bacterial infection by Mycobacterium

avium can cause fever, weight loss, anemia, and diarrhea. Additional bacterial

infections of the gastrointestinal tract commonly cause diarrhea, weight loss, anorexia

(loss of appetite), and fever. Also, during advanced AIDS, diseases caused by protozoal

parasites, especially Toxoplasmosis of the nervous system, are common.

In addition to PCP, people with AIDS often develop other fungal infections.

Thrush, an infection of the mouth by the fungus Candida Albicans, is common in the

early symptomatic phase of AIDS. Other infectious fungi include species of the genus

Cryptococcus, a major cause of Meningitis in up to 13 percent of people with AIDS.

Also, infection by the fungus Histoplasma Capsulatum affects up to 10 percent of

people with AIDS, causing general weight loss, fever, and respiratory complications or

severe central nervous system complications if the infection reaches the brain.

Viral opportunistic infections, especially with members of the Herpes virus

family, are common in people with AIDS. One Herpes family member, Cytomegalovirus

(CMV), infects the retina of the eye and can result in blindness. Another herpes virus,

Epstein-Barr virus (EBV), may result in a cancerous transformation of blood cells.

Infections with Herpes Simplex Virus types 1 and 2 are also common and result

in progressive sores around the mouth and anus.

Many people with AIDS develop cancers, the most common types being B-cell

Lymphoma and Kaposi?s Sarcoma. Kaposi?s Sarcoma?a cancer of blood vessels

that results in purple lesions on the skin that can spread to internal organs and cause

death?occurs mainly in homosexual and bisexual men. Although the cause of KS is

unknown, a link between KS and a new type of herpes virus was discovered in 1994.

Human Immunodeficiency Virus (HIV)

The causative agent of AIDS is HIV, a human retrovirus. Researchers have

known since 1984 that HIV enters human cells by binding with a receptor protein known

as CD4, located on human immune-cell surfaces. HIV carries on its surface a viral

protein known as cp120, which specifically recognizes and binds

еще рефераты
Еще работы по на английском языке