"Acquired Immune Deficiency Syndrome", was described for the first time in 1981 as symptom complex (syndrome). 1984 the third human "Retro Virus" (HTLV-III), was called in the meantime "Human Immunodeficiency Virus" or "HIV", proven by R.C.Gallo clearly as exciter of the AIDS illness. The virus, however, was already isolated in 1983 by L. Montagnier, Pasteur Institute, Paris, who has been awarded with the Nobel Prize in 2008.
According R.C.Gallo, HIV possesses like other retrovirus RNA (Ribonucleic Acid) as genetic material. After penetration into the cell the RNA is written back (retro) by a viral enzyme, the Reverse Transcriptase, into an appropriate DNA molecule. The DNA of the virus moves into the cell core, inserts themselves into the chromosomes and creates the conditions for the increasing of the virus. As landlord cell serves a T4-Lymphozyt, i.e. a white blood corpuscle, which adjust the immune answer. The virus can remain there latently available, until the cell is immunologically stimulated by another infection. Then it increases and the virus partikel quasi "perforate the cell", i.e. the Lymphocyte dies. This reduction of the T4-Cells makes susceptibly to "opportunistic infections", which are harmless for healthy persons e.g. pneumonias for the concerning by the exciter "Pneumocystis carinii", a widespread, but usually harmless exciter.
At the beginning, homosexuals were affected by the AIDS illness, then the infection spread since the middle of the 80's also among receivers of blood transfusions and i.v. drug dependent persons. Due to these experiences the transmission paths of the HIV illness could be determined: Full blood, blood plasma, sperm and factor VIII preparations, sex contacts as well as infections from mother to child during pregnancy.
Drug-dependent, with intravenous injection of drugs (in particular in cases of opiate dependency), became by the exchange of used syringe (the so-called "needle sharing") in addition, by sexual contacts, in particular with drug-dependent prostitutes, after the homosexuals the second largest group of risks for the HIV infections.