بحث عن What Is AIDS - بحث علمى عن What Is AIDS كامل ومنسق
AIDS stands for Acquired Immunodeficiency (or Immune Deficiency) Syndrome. It results from infection with a virus called HIV, which stands for Human Immunodeficiency Virus. This virus infects key cells in the human body called CD4-positive (CD4+) T cells. These cells are part of the body's immune system, whichfights infections and various cancers.
When HIV invades the body's CD4+ T cells, the damaged immune system loses its ability to defend against diseases caused by bacteria, viruses, and other microscopic organisms. A substantial decline in CD4+ T cells also leaves the body vulnerable to certain cancers.
There is no cure for AIDS, but medical treatments can slow down the rate at which HIV weakens the immune system. As with other diseases, early detection offers more options for treatment and preventing complications.
What Is The Difference Between HIV And AIDS?
The term AIDS refers to an advanced stage of HIV infection, when the immune system has sustained substantial damage. Not everyone who has HIV infection develops AIDS.
When HIV progresses to AIDS, however, it has proved to be a universally fatal illness. Few people survive five years from the time they are diagnosed with AIDS, although this is increasing with improvements in treatment techniques.
Experts estimate that about half the people with HIV will develop AIDS within 10 years after becoming infected. This time varies greatly from person to person, however, and can depend on many factors, including a person's health status and health-related behaviors.
People are said to have AIDS when they have certain signs or symptoms specified in guidelines formulated by the U.S. Centers for Disease Control and Prevention (CDC).
The CDC's definition of AIDS includes:
• All HIV-infected people with fewer than 200 CD4+ T cells per cubic millimeter of blood (compared with CD4+ T cell counts of about 1,000 for healthy people)
• People with HIV infection who have at least one of more than two dozen AIDS-associated conditions that are the result of HIV's attack on the immune system
AIDS-associated conditions include:
• Opportunistic infections by bacteria, fungi, and viruses. Opportunistic infections are infections that are rarely seen in healthy people but occur when a person's immune system is weakened.
• The development of certain cancers (including cervical cancer and lymphomas).
• Certain autoimmune disorders.
Most AIDS-associated conditions are rarely serious in
healthy individuals. In people with AIDS, however, these infections are often severe and sometimes fatal because the immune system is so damaged by HIV that the body cannot fight them off.
The History Of AIDS
The symptoms of AIDS were first recognized in the early 1980s:
• In 1981, a rare lung infection called Pneumosystis carinii pneumonia began to appear in homosexual men living in Los Angeles and New York.
• At the same time, cases of a rare tumor called Kaposi's sarcoma were also reported in young homosexual men. These tumors had been previously known to affect elderly men, particularly in parts of Africa. New appearances of the tumors were more aggressive in the young men and appeared on parts of the body other than the skin.
• Other infections associated with weakened immune defenses were also reported in the early 1980s.
Groups most frequently reporting these infections in the early 1980s were homosexuals, intravenous drug users, and people with hemophilia, a blood disorder that requires frequent transfusions. Blood and sexual transmission were therefore suspected as the sources for the spread of the infections.
In 1984, the responsible virus was identified and given a name. In 1986, it was renamed the human immunodeficiency virus (HIV).
Need To Know: Because many of the first cases of AIDS in the United States occurred in homosexual men and intravenous drug users, some people mistakenly believe that other groups of people are not at risk for HIV infection. However, anyone is capable of becoming HIV-infected, regardless of gender, age, or sexual orientation.
• Facts About AIDS As of the year 2000, nearly one million people in the U.S. were confirmed to be HIV-positive. The Centers for Disease Control and Prevention reports that 2.2 million Americans now carry the HIV virus but do not yet have symptoms. Each year, about 40,000 new HIV infections occur in the U.S. AIDS is a leading cause of death for American men and women between the ages of 25 and 44. Through June 2000, 438,795 people in the U.S. had died from AIDS (374,422 men and 64,373 women). By the end of 2000, 36.1 million people worldwide were living with HIV/AIDS, with the vast majority living in developing countries. Through 2000, 21.8 million people worldwide have died from AIDS. Between 1991 and 1996, there were more new cases of AIDS among people older than 50 than those between ages 13 and 49. Today, 11% of all new cases of AIDS in the U.S. are now in people over the age of 50. The HIV carrier rate in the U.S. is now 1 carrier for every 100 to 200 people.
How Is HIV Infection Spread?
HIV infection is spread in three ways:
• Sexual intercourse
• Direct contact with infected blood
• From an infected mother to her unborn child
However, there is much misunderstanding about the ways in which HIV infection is not spread.
Sexual Intercourse
HIV is spread most commonly by sexual contact with an infected partner. The virus can enter the body through the lining of the vagina, penis, rectum, or mouth during sexual relations.
Sexual activities that can result in HIV infection include:
• Sexual intercourse
• Anal sex (heterosexual or homosexual )
• Oral sex (heterosexual or homosexual)
Need To Know: Q: Can HIV be spread through kissing? A: Although studies have found tiny amounts of HIV in the saliva of some people with HIV, researchers have found no evidence that HIV is spread to other people through kissing. However, the CDC recommends against "French" or open-mouthed kissing because of the possibility of contact with blood if the people kissing have any cuts or sores in the mouth.
Direct Contact With Infected Blood
HIV can be spread through direct contact with infected blood:
• Through injected drugs. HIV frequently is spread among users of illegal drugs that are injected. This happens when needles or syringes contaminated with minute quantities of blood of someone infected with the virus are shared.
• In a health-care setting. Transmission from patient to health-care worker or vice-versa - via accidental sticks with contaminated needles or other medical instruments - can occur, but this is rare.
• Through a blood transfusion. 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.
From An Infected Mother To Her Unborn Child
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.
A pregnant woman can greatly reduce the risk of infecting her baby if she takes the anti-HIV drug AZT (also called zidovudine) during her pregnancy. Because the risk of transmission increases with longer delivery times, the risk can be further reduced by delivering the baby by caesarian section , a surgical procedure in which the baby is delivered through an incision in the mother's abdominal wall and uterus. Combining AZT treatment with caesarian delivery can reduce the infection rate to between 1% and 2%.
HIV also can be spread to babies through the breast milk of mothers infected with the virus.
• Women who live in countries where safe alternatives to breast-feeding are readily available and affordable can eliminate the risk of transmitting the virus through breast milk by bottle-feeding their babies.
• In developing countries, however, where such safe alternatives are not readily available or economically feasible, breast-feeding may offer benefits that outweigh the risk of HIV transmission.
How Is HIV Infection Not Spread?
Research indicates that HIV is NOT transmitted by casual contact such as:
• Touching or hugging
• Sharing household items such as utensils, towels, and bedding
• Contact with sweat or tears
• Sharing facilities such as swimming pools, saunas, hot tubs, or toilets with HIV-infected people
• Coughs or sneezes
In short, studies indicate that HIV transmission requires intimate contact with infected blood or body fluids (vaginal secretions, semen, pre-ejaculation fluid, and breast milk). Activities that don't involve the possibility of such contact are regarded as posing no risk of infection.
Need To Know: Q: Is it safe to share a household with an HIV-infected person? A: Studies of families of HIV-infected people have found that HIV is not spread through sharing utensils, towels, bedding, or toilet facilities. Behaviors that increase the likelihood of contact with blood from an HIV-infected person, such as sharing a razor or toothbrush, should be avoided.
A Brief History of the Emergence of AIDS
In 1981, clinical investigators in New York and California observed among young, previously healthy, homosexual men an unusual clustering of cases of rare diseases, notably Kaposi's sarcoma (KS) and opportunistic infections such as Pneumocystis carinii pneumonia (PCP), as well as cases of unexplained, persistent lymphadenopathy (CDC, 1981a,b, 1982a; Masur et al., 1981; Gottlieb et al., 1981; Friedman-Kien, 1981). It soon became evident that these men had a common immunologic deficit, an impairment in cell-mediated immunity resulting from a significant loss of "T-helper" cells, which bear the CD4 marker (Gottlieb et al., 1981; Masur et al., 1981; Siegal et al., 1981; Ammann et al., 1983a).
The widespread occurrence of KS and PCP in young people with no underlying disease or history of immunosuppressive therapy was unprecedented. Searches of the medical literature, autopsy records and tumor registries revealed that these diseases previously had occurred at very low levels in the United States (CDC, 1981b; CDC, 1982f).
KS, a very rare skin neoplasm, had affected mostly older men of Mediterranean origin or cancer or transplant patients undergoing immunosuppressive therapy (Gange and Jones, 1978; Safai and Good, 1981). Before the AIDS epidemic, the annual incidence of Kaposi's sarcoma in the United States was 0.02 to 0.06 per 100,000 population (Rothman, 1962a; Oettle, 1962). In addition, a more aggressive form of KS that generally occurred in younger individuals was seen in certain parts of Africa (Rothman, 1962b; Safai, 1984a). By 1984, never-married men in San Francisco were found to be 2,000 times more likely to develop KS than during the years 1973 to 1979 (Williams et al., 1994). As of Dec. 31, 1994, 36,693 patients with AIDS in the United States with a definitive diagnosis of KS had been reported to the CDC (CDC, 1995b).
PCP, a lung infection caused by a pathogen to which most individuals are exposed with no undue consequences, was extremely rare prior to 1981 in individuals other than those receiving immunosuppressive therapy or among the chronically malnourished, such as certain Eastern European children following World War II (Walzer, 1990). A 1967 survey, for example, found only 107 U.S. cases of PCP reported in the medical literature up to that point, virtually all among individuals with underlying immunosuppressive conditions or who had undergone immunosuppressive therapy (Le Clair, 1969). In that year, CDC became the sole supplier in the United States of pentamidine isethionate, then the only recommended PCP therapy, and began collecting data on each PCP case diagnosed and treated in this country. After reviewing requests for pentamidine in the period 1967 to 1970, researchers found only one case of confirmed PCP without a known underlying condition (Walzer et al., 1974). In the period immediately prior to the recognition of AIDS, January 1976 to June 1980, CDC received only one request for pentamidine isethionate to treat an adult in the United States who had PCP and no underlying disease (CDC, 1982f). In 1981 alone, 42 requests for pentamidine were received to treat patients with PCP and no known underlying disorders (CDC, 1982f). By Dec. 31, 1994, 127,626 individuals with AIDS in the United States with definitive diagnoses of PCP had been reported to the CDC (CDC, 1995b).
Another rare opportunistic disease, disseminated infection with the Mycobacterium avium complex (MAC), also was seen frequently in the first AIDS patients (Zakowski et al., 1982; Greene et al., 1982). Prior to 1981, only 32 individuals with disseminated MAC disease had been described in the medical literature (Masur, 1982a). By Dec. 31, 1994, the CDC had received reports of 28,954 U.S. AIDS patients with definitive diagnoses of disseminated MAC (CDC, 1995b).
What Causes AIDS?
HIV is a type of virus called a retrovirus. Like all viruses, it must invade the cells of other organisms to survive and reproduce. HIV multiplies in the human immune system's CD4+ T cells and kills vast numbers of the cells it infects. The result is disease symptoms.
Nice To Know: There are two forms of HIV: HIV-1 is the more common and more potent form. This form of HIV has spread throughout the world. HIV-2, which is less potent that HIV-1, is found predominantly in West Africa. It is also more closely related to two HIV-like viruses found in monkeys. There also are different strains of the virus, which makes it difficult to find one single treatment.
About The Immune System
Our bodies use a natural defense system to protect us from bacteria, fungi, viruses, and other microscopic invaders. This system includes general, nonspecific defenses as well as weapons custom-designed against specific health threats:
• Innate, or nonspecific, immunity is the first line of defense. Our skin, tears, mucus, and saliva, as well as the swelling that occurs after an infection or injury, contain types of immune cells and chemicals that attack disease-causing agents attempting to invade the body.
• Adaptive, or specific, immunity uses specialized cells and proteins called antibodies to attack invaders that get past the first line of defense. These weapons target specific proteins called antigens , found on the surface of the invading organism. The immune system can quickly rally these custom-tailored defenses if this particular invader attacks again.
There are two types of adaptive immune responses:
• The humoral immune response involves the action of specialized antibody-producing white blood cells. The antibodies (proteins produced by the immune system to fight infectious agents such as viruses), which circulate in the blood and other body fluids, can recognize specific antigens (substances that stimulate the production of antibodies). They latch onto the viruses, bacteria, toxins, and other substances that bear these antigens, targeting them for destruction.
• The cell-mediated immune response involves the action of another group of specialized white blood cells that direct and regulate the body's immune responses or directly attack cells that are infected or cancerous.
How Do White Blood Cells Help Fight Disease?
White blood cells, particularly macrophages and B and T lymphocytes , play central roles in the immune system's defenses against viruses and other foreign invaders.
• Macrophages contribute to both nonspecific and specific immune responses. These versatile cells act as scavengers, engulfing and digesting microbes and other foreign material in a cell-eating process called phagocytosis . They also, upon encountering an invading organism, release chemical messengers that ,,,,, other cells of the immune system and summon T lymphocytes to the scene.
• B lymphocytes, or B cells, serve as the body's antibody factories. Each antibody is targeted to recognize and bind to an antigen from a specific invader. When antibodies circulating through blood and body fluids encounter this invader, they mark it for destruction.
• T lymphocytes, or T cells, are part of the cellular immune response. Some T cells, like CD4+ T cells (also called "helper" T cells), direct and regulate the body's immune responses. Others are killer cells that attack cells that are infected or cancerous.
How Does HIV Infection Become Established In The Body?
Researchers have found evidence that immune-system cells called dendritic cells may begin the process of infection. After exposure, these special cells may bind to and carry the virus from the site of infection to the lymph nodes, where other immune system cells become infected.
HIV targets cells in the immune system that display a protein called CD4 on their surface. Such cells are called CD4-positive (CD4+) cells.
Nice To Know: When HIV encounters a CD4+ cell, a protein called gp120 that protrudes from HIV's surface recognizes the CD4 protein and binds tightly to it. Another viral protein, p24, forms a casing that surrounds HIV's genetic material. HIV's genetic material contains the information needed by the virus to infect cells, produce new copies of virus, or cause disease. For example, these genes encode enzymes that HIV requires to reproduce itself. Those enzymes are reverse tran,,,,,,ase , integrase, and protease.
How HIV Causes AIDS
HIV disease is characterized by a gradual deterioration of immune function. Most notably, crucial immune cells called CD4+ T cells are disabled and killed during the typical course of infection. These cells, sometimes called "T-helper cells," play a central role in the immune response, signaling other cells in the immune system to perform their special functions.
A healthy, uninfected person usually has 800 to 1,200 CD4+ T cells per cubic millimeter (mm3) of blood. During HIV infection, the number of these cells in a person's blood progressively declines. When a person's CD4+ T cell count falls below 200/mm3, he or she becomes particularly vulnerable to the opportunistic infections and cancers that typify AIDS, the end stage of HIV disease. People with AIDS often suffer infections of the lungs, intestinal tract, brain, eyes and other organs, as well as debilitating weight loss, diarrhea, neurologic conditions and cancers such as Kaposi's sarcoma and certain types of lymphomas.
Most scientists think that HIV causes AIDS by directly inducing the death of CD4+ T cells or interfering with their normal function, and by triggering other events that weaken a person's immune function. For example, the network of signaling molecules that normally regulates a person's immune response is disrupted during HIV disease, impairing a person's ability to fight other infections. The HIV-mediated destruction of the lymph nodes and related immunologic organs also plays a major role in causing the immunosuppression seen in people with AIDS.
HIV Infection in Women
OVERVIEW
The number of women with HIV (human immunodeficiency virus) infection and AIDS (acquired immunodeficiency syndrome) has been increasing steadily worldwide. By the end of 2003, according to the World Health Organization (WHO), 19.2 million women were living with HIV/AIDS worldwide, accounting for approximately 50 percent of the 40 million adults living with HIV/AIDS.
By the end of 2002, 159,271 adolescent and adult women in the United States were reported as having AIDS. Based on cases reported to the Centers for Disease Control and Prevention (CDC) through December 2002, more than 57,376 women have been infected with HIV. Among adolescent and adult women, the proportion of AIDS cases more than tripled from 7 percent in 1985 to 26 percent in 2002. Nonetheless, AIDS cases in adolescent and adult women have declined by 17 percent and have plateaued in the past 4 years, reflecting the success of antiretroviral therapies in preventing the development of AIDS.
Worldwide, more than 90 percent of all adolescent and adult HIV infections have resulted from heterosexual intercourse. Women are particularly vulnerable to heterosexual transmission of HIV due to substantial mucosal exposure to seminal fluids. This biological fact amplifies the risk of HIV transmission when coupled with the high prevalence of non-consensual sex, sex without condom use, and the unknown and/or high-risk behaviors of their partners.
Younger women are also increasingly being diagnosed with HIV infection, particularly among African-Americans and Hispanics. Through December 2002, women aged 25 and younger accounted for 9.8 percent of the female AIDS cases reported to CDC.
HIV disproportionately affects African-American and Hispanic women. Together they represent less than 25 percent of all U.S. women, yet they account for more than 82 percent of AIDS cases in women.
Women suffer from the same complications of AIDS that afflict men but also suffer gender-specific manifestations of HIV disease, such as recurrent vaginal yeast infections and severe pelvic inflammatory disease, which increase their risk of cervical cancer. Women also exhibit different characteristics from men for many of the same complications of antiretroviral therapy, such as ,,,,bolic abnormalities.
Frequently, women with HIV infection have great difficulty accessing health care, and carry a heavy burden of caring for children and other family members who may also be HIV-infected. They often lack social support and face other challenges that may interfere with their ability to adhere to treatment regimens.
الإثنين 15 مايو - 11:57
