Initially recognised in a handful of cases during the early 1980s, human immunodeficiency virus (HIV) has infected an estimated 33 million people worldwide (UNAIDS Epidemic Update, 2008), causing the acquired immunodeficiency syndrome (AIDS). In 2007 the HIV/AIDS epidemic killed approximately 2 million individuals. The central nervous system (CNS) is a major target of HIV, becoming infected in the primary stage of infection and this continues in the majority of untreated seropositive individuals throughout the course of infection.