The human immunodeficiency virus, or HIV, causes the AIDS disease. It duplicates itself after it enters white blood cells called the CD4+ T lymphocytes. The infection progresses as the virus destroys these blood cells. As the number of CD4+ T cells decline to a certain level, people with an HIV infection are susceptible to contracting specific diseases. A person has AIDS when they start contracting serious infections or when their CD4+ T lymphocytes are lower than 200 cells per μl.
CD4+ Below 200 Per μl
The normal level of CD4+ T lymphocytes is approximately 1,000 cells per μl, writes Elizabeth Corwin, Ph.D. in "Handbook of Pathophysiology." The human immunodeficiency virus can destroy 50 to 75 CD4+ T cells each year. If the number of CD4+ cells decreases to 200 cells per μl, people now have AIDS and are at great risk of contracting a pneumonia caused by the Pneumocystis jiroveci fungus.
This fungus is everywhere, but it only causes pneumonia in people who have an impaired immune system, which includes those with AIDS. It is currently the most common lung infection in people with AIDS. It can lead to respiratory failure where people need a mechanical ventilator to breathe, reinfections and lung cysts. The cysts can cause a spontaneous pneumothorax, also called a "collapsed lung," because they can rupture and leak air into the space that surrounds the lung. This can put so much pressure on the lung that it collapses.
CD4+ Below 100 Per μl
AIDS progresses further if the CD4+ cell count goes below 100 cells per μl. Now people are at risk of developing toxoplasmosis, cryptococcosis and cryptosporidiosis.
The Toxoplasma gondii parasite causes toxoplasmosis. This is actually a common parasite. In fact, 20 to 40 percent of American adults have antibodies against it, but T. gondii only causes disease in fetuses and in people with an impaired immune system, according to the Merck Manuals Online Medical Library.
People with AIDS usually develop brain lesions and encephalitis. Encephalitis is the inflammation of the brain. The Cryptococcus neoformans fungus causes cryptococcosis, which affects the lungs and brain in those who have AIDS. Cryptosporidiosis is caused by the Cryptosporidium protozoa. This infection causes diarrhea, but the diarrhea is very severe in those with AIDS.
CD4+ Below 50 Per μl
If the AIDS disease continues to progress and destroys more CD4+ T cells so there is less than 50 cells per μl, people risk contracting cytomegalovirus, mycobacterium avium complex and progressive multifocal leukoencephalopathy. Anyone who becomes infected with the cytomegalovirus carries that virus for life, as explained by "Harrison's Principles of Internal Medicine." Usually, the only people with symptoms are fetuses and those with an impaired immune system.
In AIDS, the virus affects the eyes, esophagus, stomach, intestines and brain. Mycobacterium avium complex, or MAC, is an infection caused by the Mycobacterium avium and Mycobacterium intracellulare bacteria. These bacteria normally infect the lungs, but they spread throughout the body in people with AIDS. The JC virus causes progressive multifocal leukoencephalopathy, a fatal brain disease. It is a common virus that people usually get in childhood. The virus stays dormant in the kidneys, but becomes active in AIDS due to the weak immune system.
References
- "Handbook of Pathophysiology"; Elizabeth Corwin, MSN, Ph.D., FNP; 2000
- "Harrison's Principles of Internal Medicine"; Anthony Fauci, M.D., Dennis Kasper, M.D., Dan Longo, M.D. et al.; 2008
- Merck Manuals Online Medical Library: Toxoplasmosis
