ACQUIRED IMMUNODEFICIENCY SYNDROME (AIDS)
It is a life-threatening disease caused by the human immunodeficiency virus (HIV). Two strains of HIV have been recognized: HIV-1 is responsible for most cases of AIDS, whereas HIV-2 is increasingly being found in West Africa. AIDS was first reported in 1981 in the United States. Since then over 500000 cases have been reported to the Center for Disease Control (CDC). Evidence suggests that almost everyone infected will develop symptoms within 10 years, and they will eventually develop the disease if they do not die of some other cause. The few causes of HIV-infected individuals who have not developed AIDS even after many years of being infected are being investigated.
HIV is transmitted from an infected to a non-infected person in body fluids such as blood, semen, or vaginal secretions. The major method of transmission are intimate sexual contact, contaminated needles used by intravenous drug users, and tainted blood products. Present evidence indicates that household, school, or work contacts do not result in transmission.
In the USA, most cases of AIDS have appeared in homosexual or bisexual men are in intravenous drug users. A small percentage of cases have resulted from transfusions or contaminated clotting factors used by hemophiliacs. Sadly, children can be infected before birth, during delivery, or after birth from breast-feeding. A few cases of AIDS have occurred in health care workers accidentally exposed to HIV-infected blood or body fluids, and even smaller number of cases of health care workers infecting patients has been documented. The most rapidly increasing group of AIDS patients in the United States of America is heterosexual women or men who have had sexual contact with infected person. Women in the 15- to 25-year-old age group appear to be especially likely to contract AIDS, possibly because the vaginal mucous membranes of women in this age group are thin and are a less effective barrier to the virus.
In the other countries, the pattern of AIDS cases can be different from that in the USA. For example, in Haiti and central Africa, heterosexual transmission is the major route of HIV spread. Worldwide, about 40% of AIDS are women. The World Health Organization estimates that near 27 million people have been infected by HIV.
Preventing transmission of HIV is presently the only way to prevent AIDS. The risk of transmission can be reduced by educating the public about safe sexual practices such as reducing the number of one's sexual partners, avoiding anal intercourse, and using condom. Public education also includes warnings to intravenous drug users of the dangers of using contaminated needles. Ensuring the safety of the blood supply is another important preventive measure. In April, 1985, a test for HIV antibodies in blood became available. Heat treatment of clotting factors taken from blood has also been effective in preventing transmission of HIV to hemophiliacs.
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HIV infection begins when the virus binds to a CD4 surface molecule. The CD4 molecule is found primarily on helper T cells but also on certain monocytes, macrophages, neurons and neuroglial cells. Once attached to CD4 molecule, the virus injects its genetic material (RNA) and enzymes into the cell. The viral RNA and enzymes produce DNA that can direct the formation of new HIV ribonucleic acid and proteins, that is, additional viruses that can infect other cells. Most of the manifestations of AIDS can be explained by the loss of helper T cell functions or the infection of the other cells with CD4 molecules. Without helper T cells, cytotoxic T-cell and B-cell activation is impaired, and specific resistance is suppressed.
Following infection by the HIV, within 3 weeks to 3 months, some patients develop an acute (sudden0 mononucleosis-like syndrome that can last up to 14 days. Symptoms include fever, sweats, fatigue, muscle and joint aches, headache, sore throat, diarrhea, rash, and lymphadenopathy. More commonly there is a persistent version of the syndrome that lasts for several months and includes lymphadenopathy, fever and fatigue. During this time the patient becomes positive for HIV antibodies, and within a year many patients develop AIDS.
The most common clinical manifestations of AIDS include testing positive for HIV antibodies, a decrease in helper T cell numbers to fewer that 200/mm3 of blood, and the presence of opportunistic infections or Kaposi's sarcoma. Normally, there are about 1200 helper T cells/ mm3 of blood, but between the time of infection and the AIDS development the T-helpers decreases. Apparently most HIV replication takes place in the lymph nodes where helper T cells and other immune cells aggregate. As cells in the lymph nodes are destroyed, the number of circulating helper cells decreases.
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Opportunistic infections involve organisms that normally do not cause disease but can do so when the immune system is depressed. Examples include Pneumocystis carinii (pneumonia caused by intracellular protozoan); tuberculosis (caused by tuberculosal Mycobacter), syphilis (caused by pale Treponema), candidiasis (a yeast infection of the mouth or vagina caused by Candida albicans); and protozoans can cause severe, persistent diarrhea. Kaposi's sarcoma is a type of cancer that produces lesions in the skin, lymph nodes, and visceral organs. Also associated with AIDS are symptoms resulting from the effects of HIV of the nervous system, including motor retardation, behavioral changes, progressive dementia and possibly psychosis.
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