HIV Spread
AIDS (acquired immunodeficiency syndrome) is caused by an infection with HIV (human immunodeficiency virus). As the Journal of the American Medical Association explains, HIV is spread via bodily fluids. HIV can be transmitted during sexual intercourse through the exchange of semen or vaginal secretions. It can also be spread among intravenous drug users if they share contaminated needles. Finally, HIV can be spread by receiving a contaminated transfusion of blood or blood products, though this is rare in developed countries because they now screen all blood donations for HIV.
HIV and White Blood Cells
As Medline explains, HIV affects the immune system (hence its name). The virus infects special white blood cells called CD4 helper lymphocytes. These cells are important for the immune system because they help coordinate its ability to fight off infections and certain kinds of cancer. When HIV infects these cells, it kills them. The body can make more of these white blood cells to compensate for their depletion, but over time the infection reduces the number of these white blood cells. When the CD4 helper lymphocyte numbers get low enough the patient is diagnosed with AIDS.
AIDS
A patient is typically diagnosed with AIDS if he has a CD4 helper lymphocyte count of under 200 (measured by analyzing a blood sample) or if he develops a serious disease (such as cancer or an infection) as a result of a weakened immune system. Once a patient has AIDS he is much more susceptible to developing serious infections, including some that normally do not affect people with healthy immune systems. This includes problems with tuberculosis, cytomegalovirus, progressime multifocal leukoencephalopathy (a serious viral infection of the brain) and many kinds of fungi (including candida infections). Because people with AIDS have very weak immune systems, any sort of infection can be life threatening because the immune system may not be able to contain the infection or keep it from spreading.
