Introduction

• The acquired immunodeficiency syndrome, or AIDS, is a devastating disease that has affected millions of people throughout the world. According to the Center for Disease Control, more than 583,298 people in the United States have died from the disease since its introduction to America. In 2007 alone,14,561 people died from AIDS. With such a devastating disease, it's important to understand how it starts.
  
  

Transmission

• AIDS starts with the transmission of the human immunodeficiency virus (HIV). This virus can be transmitted from person to person through three main ways. First is through the exchange of sexual fluids. This can occur both heterosexually and homosexually, and the disease can be spread through vaginal, anal and oral sex. Second is through the introduction of infected blood. Most commonly this occurs through the use of dirty needles among intravenous drug users, but can also happen through blood transfusions or accidental exposure to infected blood in an open wound or through a needle stick. Thirdly, the virus can be transmitted from mother to baby. This occurs during the birth process when the baby comes in direct contact with the mother's infected fluids. In some cases, the disease can also be spread through infected mothers who breastfeed their children.
  
  

Infection

• Once the virus has entered the bloodstream it begins to multiply and infect the body. Since viruses do not have all the internal structures needed to multiply on their own, the HIV virus hijacks healthy immune system cells by inserting its genetic material into the healthy cell. From there it can use the internals of the immune cell to replicate itself and continue infecting other healthy immune cells.
  
  

T-Cells

• The immune cell of choice for the HIV virus are the CD4 T-cells. These cells are an important part of fighting off diseases in the body. As more cells are affected, the HIV diagnosis transforms into an AIDS diagnosis. The Center for Disease Control (CDC) has set out guidelines for defining an AIDS diagnosis, with one factor being the CD4 cell count. A healthy individual normally has between 800 and 1,000 cells per cubic milliliter of blood. Once that count drops below 200, by CDC definition, the patient has AIDS.
  
  

Opportunistic Infections

• Another way in which the CDC defines AIDS is through the presence of opportunistic infections that the body's immune system normally is capable of fighting off. An opportunistic infection is any disease that takes advantage of the body while its defenses are down. Common opportunistic infections that warrant an AIDS diagnosis include serious cases of pneumocystis pneumonia (PCP), chronic herpes infections, candidiasis (thrush), tuberculosis and toxoplasmosis. Since the immune system is already compromised during these infections, many of them can become deadly. In fact, most people do not die because of the AIDS virus itself, but from the opportunistic infections that take hold during the infection.