AIDS (Acquired Immunodeficiency syndrome)
Acquired immunodeficiency syndrome (AIDS) was first recognized as a distinct disease in 1981 and is considered the first great pandemic disease of the second half of 20th century. The diseases appears to have begun in central African as early as 1950s and the United Nations report in 2000 estimates that from 1981 to 2000, 56 million people have been infected with human immunodeficiency virus (HIV)/AIDS, 20 million people have already died, and 36 million are still surviving with the disease.

The Mechanism of Infection
HIV infection normally occurs first in macrophages, an antigen-presenting cell that has a very low level of CD4 proteins on its surface. The viral protein gp 120 then interacts with another macrophage protein (CCR5) which acts as a coreceptor for HIV and together with CD4 forms the docking site where the HIV envelop fuses with the host cell membrane allowing insertion of the viral nucleocapsid.

After HIV has infected them macrophage, a different form of gp 120 proteins is made Which in turn binds to a different coreceptor called CXCR4 on T-cells (T-lymphocytes). HIV then enters and destroys the T-cells. Thus, HIV first infects macrophages and the to T-cells. The net result of HIV infection is the systematic destruction of macrophages and T-cells resulting in a catastrophic breakdown of immunity in the body of the victim.