What is the evidence that HIV causes AIDS?

(The image representing HIV is under CC BY-SA 4.0. license. Thomas Splettstoesser (www.scistyle.com). No changes were made).

HIV - human immunodeficiency virus

AIDS - acquired immunodeficiency syndrome.


It's well known that HIV causes AIDS.


1
But how do scientists know that?
I understand that researches once isolated HIV from patients with AIDS symptoms.

How reliable is that evidence?

Did they even try to identify this virus in people without AIDS symptoms?

In other words, how did scientists become sure that HIV->AIDS is causation (cause and effect/cause-and-effect relations) rather than correlation.

How much people did they scan?

Is there any stronger evidence that HIV causes AIDS than just isolation (like an experiment)?
(It's hard to believe that someone on the face of the Earth among humanity could agree to take part in such an experiment (HIV injection into one's organism with subsequent health state monitoring)).

2
HIV stands for human immunodeficiency virus.
So, we can't use animals to make that experiment.
Is that correct?
Why exactly?

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