AIDS (acquired immune deficiency syndrome or acquired immunodeficiency syndrome) is the last and hardest stadium of HIV (human immunodeficiency virus). HIV virus destroys human immune system which is responsible for fighting all kind of viruses and diseases. Simply it makes human organism way too weak to be able to resist infections.

Before HIV become AIDS, virus can live in human body even 15 or more years, and infected person usually looks normal without any kind of differences, so its impossible to recognize infected people without medical examination. So if someone is HIV positive it doesn't mean he has an AIDS, but when AIDS occur death is inevitable.
The sad true about HIV virus is that there is no vaccine or cure yet, although there is treatments that can slow the virus progression. That treatment consists of highly active antiretroviral therapy, or HAART. Without this therapy progression from HIV to AIDS is much faster and survival time after developing AIDS is only about 9 months. HAART can increase survival time by between 4 and 12 years. Treatments continue to be developed every day so estimates of survival time are likely to continue to change.

Map representing adult HIV prevalence in percents for
particular countries at the end of 2005 (taken from Wikipedia).

Since there are not particular symptoms, people infected with AIDS may have fevers, swollen glands, sweats (especially at night), chills, weakness, and weight loss. Due to reduced immune system those people are much more liable to diseases and infections that usually don't develop in individuals with healthy immune systems. Most of these infections are caused by viruses, bacteria and fungi. HIV virus affects almost all organs so infected people have an increased risk of developing cancers (especially Kaposi's sarcoma, cervical cancer and lymphomas known as cancers of immune system).

Anyway many people are unaware that they have HIV and they continue to spread infections. HIV can be detected by typical HIV tests that detect HIV antibodies in plasma, serum, oral fluid, dried blood spot or urine. However, time between infection and development of antibodies that can be detected can vary and it can take between 3-6 months. This time is called the window period.

HIV virus has shield containing proteins and fat so its very sensitive in touch with substances such as alcohol or any other kind of disinfectants. Virus is very compliant in outside environment so it can live only for few minutes outside of human body. Its also very sensitive at higher temperatures. The only way to survive outside of human body is at very low temperatures (below 70 degrees).

HIV virus originate from SIV (Simian Imunotropic Virus) and scientists believe its evolution took period of several hundreds years.

HIV virus can be found in almost all types of body fluids including blood, lymph, vaginal fluid, semen, preseminal fluid and breast milk. Although it can be found in saliva, tears and urine, its impossible to get HIV infection from these fluids because they contain very small percent of virus.

The most common way of HIV transmission is by sexual activity (in the any form of vaginal, anal or oral penetrations) with infected person, especially if ejaculation is included because semen contains high level of virus. During sex, only condoms (male of female types) can reduce the risk of infection. Also HIV virus spreads by sharing needles and syringes (usually for drug injection) or transfusions of infected blood, so medical equipment for those kind of interventions must be sterile. Babies can also be infected by their mothers (MTCT - mother to child transmission) during or before birth. There are methods such as antiretroviral drugs, caesarean delivery and formula feeding that can reduce risk of transfering infection. Also babies can get infection during breast-feeding.
There are many other ways of spreading virus such as being stuck with infected needles that can happen to health care workers or after infected blood gets into a open cut somewhere on human body. Although those cases are extremely rare, people, especially medical workers should pay particular attention while working with injured people who is infected (especially in cases of open wounds).
Insects such as mosquitos or animals can not spread infection because HIV virus infects CD4 cells which are only present in human blood.

Anyway there are also many delusions about spreading HIV virus such as using swimming pool, common social relations such as shaking hands, hugging, talking with infected person, eating food that was made by infected or being in the same room. All these mistakes usually lead to asocial and immoral behavior against infected people and can seriously hurt their feelings.

Many people (not only infected) and organizations all around the world are fighting against those prejudices in society. The Red ribbon is a symbol which represent solidarity with HIV positive people.

Every day about 8000 people die of aids, so its probably one of the worst diseases in human history.

Red ribbon represents
solidarity with infected.