How the spread of AIDS can be controlled?
People should wear condoms every time they have sex, and handle blood products carefully. It's not a perfect system but it's the best one we've got so far.
Why there has been no medicine found out?
Because it's a complicated retrovirus, and probably a lot of different viruses.
Is there possibility of curing AIDS fully?
Not yet, though there might eventually be. We can't predict the future.