HIV stands for 'human immunodeficiency virus'. HIV is a retrovirus that infects cells of the human immune system (mainly CD4 positive T cells and macrophages-key components of the cellular immune system), and destroys or impairs their function. Infection with this virus results in the progressive depletion of the immune system, leading to 'immune deficiency'.
The immune system is considered deficient when it can no longer fulfill its role of fighting off infection and diseases. Immunodeficient people are much more vulnerable to a wide range of infections, most of which are very rare among people without immune deficiency. Diseases associated with severe immunodeficiency are known as 'opportunistic infections', because they take advantage of a weakened immune system.
AIDS stands for 'acquired immunodeficiency syndrome' and describes the collection of symptoms and infections associated with acquired deficiency of the immune system. Infection with HIV has been established as the underlying cause of AIDS. The level of HIV in the body and the appearance of certain infections are used as indicators that HIV infection has progressed to AIDS.
Most people infected with HIV do not know that they have become infected, because no symptoms develop immediately after the initial infection. Some people have a glandular fever-like illness (with fever, rash, joint pains and enlarged lymph nodes), which can occur at the time of seroconversion. Seroconversion refers to the development of antibodies to HIV and usually takes place between 6 weeks and 3 months after an infection has occurred.
Despite the fact that HIV infection does not cause any initial symptoms, an HIV-infected person is highly infectious and can transmit the virus to another person. The only way to determine whether HIV is present in a person's body is by taking an HIV test.
HIV infection causes a gradual depletion and weakening of the immune system. This results in an increased susceptibility of the body to infections and can lead to the development of AIDS.
The term AIDS applies to the most advanced stages of HIV infection.
The majority of people infected with HIV, if not treated, develop signs of AIDS within 8-10 years. AIDS is identified on the basis of certain infections, grouped by the World Health Organization:
Stage I. HIV disease is asymptomatic and not categorized as AIDS
Stage II. (includes minor mucocutaneous manifestations and recurrent upper respiratory tract infections)
Stage III. (includes unexplained chronic diarrhea for longer than a month, severe bacterial infections and pulmonary tuberculosis) or
Stage IV. (includes Toxoplasmosis of the brain, Candidiasis of the oesophagus, trachea, bronchi or lungs and Kaposi's Sarcoma) HIV disease is used as indicators of AIDS.
Most of these conditions are opportunistic infections that can be treated easily in healthy people.
In addition, the Centers for Disease Control and Prevention (CDC) defines AIDS on the basis of a CD4 positive T cell count of less than 200 per mm3 of blood.
CD4 positive T cells are critical in mounting an effective immune response to infections. The World Health Organization's (WHO) recommendations for the start of antiretroviral (ARV) therapy are based on the above-mentioned definitions. WHO recommends that HIV-infected adolescents and adults with these infections and/or a T cell count of 200 per mm3 start antiretroviral therapy.
The length of time can vary widely between individuals. With a healthy lifestyle, the time between infection with HIV and becoming ill with AIDS can be 10-15 years, sometimes longer. Antiretroviral therapy can slow down the progression of AIDS by decreasing viral load in an infected body.