1/2. In 1981, doctors in the US were puzzled by cases of cancers and lung conditions they were seeing in young homosexual men: diseases that were extremely rare in this age group. They were to be the first patients in the West to be diagnosed with Aids, but it was not confined to the developed world. Soon it was realised that the disease known as "slim" in Africa was also Aids. Allan Little tells the story of the race to identify the cause of this new and devastating disease. Producer Geraldine Fitzgerald