HIV is probably the major STI discussed in the world today and has been a major wake up call to the world. Even though many other STI have serious consequences and can also lead to long term illness and death it has been HIV that has changed the way of life for many. There is still no cure for HIV infection although the symptoms of AIDS can be treated as they arise. Currently there are a lot of therapies including protease inhibitors and combination therapy that are helping seriously ill people and prolong life for many. These though are not a cure.
Research is on going in to vaccines but limited trials of early developments are unsuccessful.
With HIV there are no symptoms straight away. But many people don't get these symptoms. And they are also caused by lots of other common infections. For months or years being by infected HIV there may be no symptoms. But over time, symptoms of infections and diseases caused by the immune system getting weaker.