AIDS - Acquired Immuno Deficiency Syndrome

Stages Of HIV Infection
People infected with human immunodeficiency virus (HIV) go through three stages of infection. These stages are: (1) acute retroviral syndrome and asymptomatic period, (2) symptomatic HIV infection, and (3) AIDS. The length of time any person stays in each stage varies greatly and depends on many factors, including medical treatment. HIV can be transmitted during all stages of infection, even when no symptoms occur.

Acute retroviral syndrome and asymptomatic period. Most people get a flu like or mononucleosis like illness within 6 to 12 weeks after becoming infected with HIV. This illness, known as acute retroviral syndrome, usually goes away without treatment. From this point on, the infected person's blood tests positively for HIV antibodies even though symptoms usually do not develop for 2 to 12 years or more. During this early stage of infection, the patient maintains a normal number of CD4 cells--that is, more than 1,000 CD4 cells per micro litre of blood. CD4 cells are the white blood cells that are infected by HIV.

Symptomatic HIV infection. In this stage, a wide variety of mild or severe symptoms may appear. Common symptoms include tiredness, enlarged lymph glands, yeast infections, skin rashes, and dental disease. This stage of the infection may last from a few months to many years. During this time, the patient's CD4-cell count gradually declines, typically ranging between 500 to 200 CD4 cells per micro litre of blood.

AIDS is characterized by severe damage to the immune system and such opportunistic illnesses as Pneumocystis carinii pneumonia and Kaposi's sarcoma. The progressive breakdown of the immune system eventually leads to death, usually within a few years. Most people with AIDS have fewer than 200 CD4 cells per micro litre of blood, with most deaths occurring in patients with CD4-cell counts below 50.

Cause AIDS is caused by two viruses that belong to a group called retro viruses. The first AIDS virus was isolated by researchers in France in 1983 and in the United States in 1984. The virus became known as HIV-1. In 1985, scientists in France identified another closely related virus that also produces AIDS. This virus, named HIV-2, occurs mainly in Africa. HIV-1 occurs throughout the world.

How HIV is transmitted

Researchers have identified three ways in which HIV is transmitted: (1) sexual intercourse, (2) direct contact with infected blood, and (3) transmission from an infected woman to her fetus or baby. The most common way of becoming infected is through intimate sexual contact with an HIV-infected person. HIV is transmitted through all forms of sexual intercourse, including genital, anal, and oral sex.

People who inject drugs into their bodies can be exposed to infected blood by sharing hypodermic needles, syringes, or equipment used to prepare drugs for injection. In the past, transfusion and transplant recipients and people with haemophilia contracted the virus from the blood, blood components, tissues, or organs of infected donors. However, screening and testing of both donated blood and potential organ donors have virtually eliminated this hazard. Medical workers can become infected with HIV by coming into direct contact with infected blood. This may occur through injury with a needle or other sharp instrument used in treating an HIV-infected patient. A few patients became infected while receiving treatment from an HIV-infected American dentist and from a French surgeon.

An infected pregnant woman can transmit the AIDS virus to her fetus even if she has no symptoms. Transmission may also occur from an HIV-infected mother to her baby through breast-feeding.

Studies indicate that HIV is not transmitted through air, food, or water, or by insects. No known cases of AIDS have resulted from sharing kitchens or utensils, bathrooms, locker rooms, shower rooms, living space, or classrooms.

Medical care for HIV infection and AIDS

Diagnosis. Tests for detecting evidence of HIV-1 in the blood became widely available in 1985. The tests for detecting HIV-2 became widely available in 1992. HIV tests determine the presence of antibodies to the AIDS virus. Antibodies are proteins produced by certain white blood cells to react with specific viruses, bacteria, or foreign substances that enter the body. The presence of antibodies to HIV indicates infection with the virus.

Tests that directly measure the amount of HIV in the blood have been developed. These tests enable doctors to predict the future health of with HIV and estimate their survival time. In 1996, the first home tests for HIV became available in the United States. People send in a dried blood spot by post, then use an identification number to learn results confidentially by telephone.

People with HIV infection are diagnosed as having AIDS when tests indicate that they have fewer than 200 CD4 cells per micro litre (0.000001 litre) of blood or when they develop one or more opportunistic illnesses. All HIV-infected patients should have their health closely monitored by a doctor, and receive periodic blood tests to measure the levels of virus and CD4 cells in their blood.

Treatments have been developed, but no cure for HIV infection or AIDS has yet been found. Scientists have worked to understand how HIV infects and damages human cells since AIDS was identified. In one important discovery, researchers learned that HIV uses an enzyme called reverse transcriptase to reproduce in CD4 cells. Because this enzyme is not normally found in human cells, scientists focused on developing drugs that block its action. These efforts led to development of a class of antiviral drugs called reverse transcriptase inhibitors. The first of these drugs was zidovudine, commonly known as AZT.

AZT and other reverse transcriptase inhibitors produce toxic side effects, including severe anaemia that requires blood transfusions. HIV also develops resistance to these drugs when they are given singly. Doctors combine the drugs and vary the order in which they are given to improve their effectiveness.

In 1995 and 1996, the first three protease inhibitors--indinavir, ritonavir, and saquinavir--were approved for treating HIV. These antiviral drugs block the action of protease, another HIV enzyme not found in human cells. Protease inhibitors block a later step in HIV reproduction than do reverse transcriptase inhibitors.

In 1996, several studies showed that certain combinations of anti-viral drugs could decrease HIV in the blood to undetectable levels. Although HIV appears to persist inside CD4 cells, the studies raised hope that combination therapy can control reproduction of the virus. The research also raised hope for an eventual cure. But the drugs must be taken in large quantities for a long time, and HIV may develop resistance to them. Doctors need to determine which combinations of drugs are safest and most effective over the long term.

Doctors also prevent and treat opportunistic infections in AIDS patients. Pneumocystis carinii pneumonia can be prevented with specific antibiotics. Doctors use biological substances called interferons to treat Kaposi's sarcoma (see INTERFERON). Researchers believe any eventual cure for AIDS must stop the growth of the virus, prevent opportunistic illnesses, and restore normal function to the immune system.

Prevention. To prevent transmission of HIV, sexual contact with anyone who is or might be infected with the virus must be avoided. The most effective preventive strategies are to refrain from all sexual intimacy or restrict sexual intimacy to one uninfected person. Health authorities have recommended that a condom be used every time sexual intercourse occurs with a person who is infected with HIV or whose infection status is unknown. Drug users should never share hypodermic needles, syringes, or other injection equipment. Research has shown that AZT reduces the risk of transmission from an infected woman to her fetus or baby. Doctors administer AZT and other anti-viral drugs to HIV-infected women during pregnancy and labour, and to their newborn babies. Doctors advise HIV-infected women not to breast-feed their infants.

The tests to detect evidence of HIV-1 are used to screen all blood donated in many countries. These tests have greatly increased the safety of transfusions. Screening for HIV-2 began in 1992.

There are guidelines for preventing the transmission of HIV in treatment and care centres. Doctors, dentists, and other medical workers now wear gloves, masks, and other protective clothing during many examinations and procedures.

Researchers are working to develop safe, effective, and economical vaccines against HIV infection. However, even if HIV transmission were to stop, AIDS cases would still occur for many years. This is because millions of people worldwide are already infected with the virus and have yet to develop the disease. As a result, scientists are attempting to develop vaccines to boost the immune systems of people infected with HIV.

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