Acquired immunodeficiency syndrome, or AIDS, is the disease caused by infection with human immunodeficiency virus 1, or HIV. The World Health Organization estimates that as of 2010, HIV has resulted in 25 million AIDS-related deaths since it was identified in the 1980s. Data from 2008 indicates that 33.4 million people are living with HIV/AIDS; 2.7 million new HIV infections are estimated to occur each year, with 2 million AIDS-related deaths.
HIV Infects White Blood Cells
HIV infects virtually all types of white blood cells, but effects are most particularly pronounced for helper, or CD4, T cells. In healthy individuals, helper T cells usually facilitate effective immune responses to fight infections. When infected by HIV, their functions become compromised and the infection can induce these cells to die or be killed by other immune responses. HIV infection of other white blood cell types, including CD8 T cells, dendritic cells and macrophages, also subverts normal cell functions.
Progressive Loss of Cell Numbers
As of June 2010, the progressive and substantial loss in the numbers of helper T cells is the most reliable immune correlate of HIV/AIDS available to date; it is used to show progression from HIV infection to AIDS disease. The loss of helper T cells, and other white blood cell numbers, and functions makes the immune system so weakened that otherwise benign infections in healthy individuals can be fatal for those infected with HIV.
Rise in Amount of HIV
While the numbers of T helper cells fall, the amount of virus detected rises. Viruses can be detected by testing for immune responses (antibodies) which have developed into HIV and by testing for viral proteins, such as P24. Viral replication cannot be contained by an immune system weakened by chronic HIV infection, so the virus is able to undergo virtually unchecked viral replication. Viral load is a key measurement used to indicate disease progression from HIV to AIDS.
Opportunistic Infections
Opportunistic infections occur when immune responses are severely compromised by HIV infection and mark progression to AIDS. The organisms causing opportunistic infections can be bacterial, protozoal, viral and fungal. In addition, there are a number of other malignancies that are associated with HIV/AIDS such as Karposi's sarcoma and lymphoma.
Tuberculosis is the bacterial disease most frequently associated with progression from HIV to AIDS. Tuberulosis infects nearly two-thirds of the world's population. According to AVERT, there were 1.8 million deaths as a result of tuberculosis in 2008; an estimated 500,000 of those who died from tuberculosis were also infected with HIV.
AIDS Diagnosis
According to AVERT, AIDS diagnosis can differ by location. For example, in the U.K., AIDS is diagnosed by the occurrence of one or more opportunistic infections or cancers. In the U.S., a very low T helper cell number can be used to diagnose AIDS without opportunistic infections. However, individuals with HIV can become very ill in the absence of an AIDS diagnosis.
