HIV/AIDS may not seem to be the scourge it was 20 years ago, but more than a million people are affected every year. DW's science desk has compiled the must-know facts.
1. More than 35 million people worldwide are HIV-positive - two-thirds of them live in sub-Saharan Africa. South Africa is the most heavily affected country; one in six people there is infected. HIV is more or less a fact of life in South Africa, to the extent that the South African version of the children's show "Sesame Street" includes the fuzzy, yellow, HIV-positive puppet, Kami.
2. In heterosexual sexual relations, HIV is more easily transmitted from men to women than from women to men. If a man is circumcised, however, it can reduce the risk of infecting a woman by 60 percent.
3. HIV and AIDS are not curable, but they can be held in check. Antiretroviral medication prevents the virus from multiplying in the body. Antiretroviral therapy consists of three or more drugs that the patient has to take for the rest of their lives. Such treatment has reduced the death rate from HIV by around 80 percent.
4. The spread of HIV after 1990 caused life expectancy in many countries to decline dramatically - mostly in Africa. Then, a large-scale introduction of antiretroviral medication increased life expectancy again: in South Africa, for example, average life expectancy climbed from 54 years in 2005 to 60 in 2011.
5. Due to the pharmaceutical companies' hold on patents that prevent generic versions from being produced, drugs used to combat HIV are expensive - a therapy can cost several thousand dollars a month. This has prevented large-scale use in African countries, and the trend continues: the World Health Organization estimates that 19 million HIV-positive people still lack access to the appropriate drugs.
6. There is no 100-percent-effective vaccine against HIV, and there have been few clinical studies on vaccination for humans. One vaccination tested on people in Thailand until 2009 appeared to reduce the risk of contracting HIV by a quarter.
7. One factor that complicates the development of a vaccine is how HIV quickly mutates, including in the bodies of those infected. There is a staggering variety of HIV pathogens - although two varieties are the main culprits in seriously impairing the immune system and causing illness.
8. It takes up to six weeks for an infected person to develop antibodies, and HIV tests are ineffective during this time. Those infected often experience a so-called primary HIV infection, which consists of a flu-like illness, a few weeks after infection, as the immune system reacts to the virus for the first time.
9. Dreaded mix: HIV and tuberculosis. HIV-positive people have a 20 times higher risk of contracting the bacteria that causes tuberculosis. In Africa, tuberculosis is the primary cause of death among HIV-infected people.
10. South Africa's HIV policies astounded the world for a long time. In 2008, the health ministry under former President Thabo Mbeki recommended garlic, beets and olive oil to treat infection. Antiretroviral medications were denied. Those times, luckily, appear to be past.