The Human Immunodeficiency Virus, or HIV, is the causative agent of the disease AIDS. It can only be transmitted directly from person to person through bodily fluids such as blood and semen. Although it is exceedingly difficult to catch (for example hepatitis C is transmitted the same way and is far more prevalent in at-risk populations), once infected, only about three percent of the general population seems to be naturally immune to the infection. Despite modern treatments, the virus will inevitably destroy the patient's immune system over time, leading to AIDS. The highest at-risk populations (which account for the vast majority of cases) are:
- Homosexual men who engage in unprotected anal sex.
- Heterosexuals who engage in unprotected vaginal or anal intercourse when one partner has a genital sore.
- Intravenous drug users who share needles.
- Persons who use high quantities of blood products, such as hemophiliacs or those who need blood transfusions.
For persons who engage in sexual intercourse, the proper use of a condom will prevent the transmission of the disease. Recent studies have shown that circumcision also lowers the risk of infection. Programs that distribute new needles to drug users has been shown to be effective in preventing the spread of the disease. Modern blood screening techniques have lowered the risk of infection from blood products.
The virus targets T cells, part of the body's immune system, leaving the patient susceptible to opportunistic infections. This is the same mechanism that was utilized by bubonic plague, although the two diseases are unrelated. It appears that some human beings have T-Cells that are naturally resistant to attack and are immune to the virus.
Despite several attempts since the isolation of the virus in the 1990s, the virus has resisted all attempts at developing an effective vaccine.