Sometimes used synonymously, the human immunodeficiency virus, or HIV, and acquired immunodeficiency syndrome, or AIDS, are distinctly different conditions even though they have a cause and effect relationship. The possibility exists that a person might contract HIV but never develop AIDS. A person with AIDS, however, always has HIV, because HIV is the virus that causes AIDS.
HIV Infection
HIV attacks the immune system, impairing the body’s defenses against illness. "Harrison’s Manual of Medicine" states that CD4 T lymphocytes, which are the body's first line of illness-fighting cells, accept the virus on their surfaces and become receptors that enable the virus to replicate. Ordinarily CD4 T lymphocytes fight viruses, but HIV exploits a susceptibility in these cells. Once it begins to replicate, the virus goes on to destroy lymphocytes. A person with HIV infection becomes immunocompromised, but he may or may not develop AIDS. The degree of resulting immune system damage varies with the infected patient's circumstances.
AIDS
Some individuals who are infected with HIV develop AIDS. AIDS refers to an assortment of serious infections that develop when the number of CD4 T lymphocytes drops to dangerously low levels. In the absence of any real resistance, opportunistic organisms that are normally present in the body in low numbers, such as yeast, bacteria and fungi, can reproduce rapidly and infect the body. Small numbers of these organisms are kept in balance by the body as long as the immune system keeps them from multiplying. AIDS disarms the body's immunity and these normally harmless organisms flourish uncontrolled.
HIV Symptoms
According to "Current Medical Diagnosis and Treatment," some people infected with HIV live many years without displaying symptoms of HIV infection or developing full-blown AIDS. Antiviral medications can aid in keeping the viral load low enough to prevent immune system damage. For others, systemic complaints and weight loss become evident. Persistent fever, night sweats, nausea, vomiting and loss of muscle mass are symptoms of HIV infection. Yet these individuals still do not display the advanced signs of infection that define full-blown AIDS.
AIDS Symptoms
The immune system of some individuals with HIV is so weakened that they develop advanced infections that have become hallmarks of AIDS. These infections include a skin cancer called Kaposi’s sarcoma, pneumocystis pneumonia, mycobacterium avium complex, toxoplasmosis of the brain, cytomegalovirus of the retina or a combination of these and other infections.
When HIV Becomes AIDS
A physician can diagnose HIV infection with a laboratory test. The diagnosis of AIDS occurs in several ways. According to "Current Medical Diagnosis and Treatment," the Centers for Disease Control and Prevention, or CDC, define the crossing of the threshold between HIV and AIDS in a number of ways. The illnesses that come with AIDS usually appear at various levels of viral load, CD4 lymphocyte and T lymphocyte count. Even without laboratory confirmation of HIV infection, the presence of any of the advanced opportunistic illnesses listed above confirms the diagnosis of AIDS. In cases in which laboratory evidence of HIV infections does exist, a physician usually identifies a co-defining illness to confirm the development of AIDS. As the viral load in HIV infection increases, T lymphocyte count decreases. The CDC states that when this count decreases to 200 cells/mcL of blood or drops to 14 percent or less of total lymphocytes, a patient is diagnosed with AIDS.
References
- "Current Medical Diagnosis and Treatment"; Stephen J. McPhee and Maxine A. Papadakis; 2010
- "Harrison's Manual of Medicine, 17th Edition"; Anthony S. Fauci, et al.; 2009
