The human immunodeficiency virus (HIV) targets cells in the immune system – the body’s defence against illness – and weakens the body’s ability to fight against infections and some types of cancer. The virus destroys white blood cells in the immune system called CD4 cells and replicates itself inside these cells.
As the virus destroys and impairs the function of immune cells, infected individuals gradually become immunodeficient. The body becomes increasingly unable to fight infections and disease and vulnerable to opportunistic infections and cancers. Immune function is typically measured by CD4 cell count.
The most advanced stage of HIV infection is acquired immunodeficiency syndrome (AIDS), which can take from two to 15 years to develop, depending on the individual.