The human immunodeficiency viruses (HIV) are two types of Lentivirus—a subgroup of retroviruses—that infect humans. Over time, HIV leads to acquired immunodeficiency syndrome (AIDS), a condition marked by the gradual breakdown of the immune system, making the body vulnerable to life-threatening opportunistic infections and cancers. Without treatment, the average life expectancy after contracting HIV is estimated to be between 9 and 11 years, depending on the specific subtype.