Human immunodeficiency virus (HIV) is a retrovirus that causes acquired immunodeficiency syndrome (AIDS, a condition in humans in which the immune system begins to fail, leading to life-threatening opportunistic infections).
Infection with HIV occurs by the transfer of blood, semen, vaginal fluid, pre-ejaculate, or breast milk. Within these bodily fluids, HIV is present as both free virus particles and virus within infected immune cells. The three major routes of transmission are unprotected sexual intercourse, contaminated needles, and transmission from an infected mother to her baby at birth, or through breast milk. Screening of blood products for HIV in the developed world has largely eliminated transmission through blood transfusions or infected blood products in these countries.
HIV in "Coming Across"
The elf Lingol inadvertantly brought HIV to his people, a consequence of his intimate relationship with Gaetan. The elves had no understanding of what was destroying their health and yet was completely resistant to their traditional healing magics.
HIV in A Different Flesh
The fact that sims could also be infected with HIV proved to be invaluable to its study. In 1988, the Terminus Disease Research Center was able to create an HIV inhibitor (HIVI) based on the study of infected sims.