Question about the origin of STD's.?

Trying to see it in simple terms. Disease either bacteria or viral can come about by a few ways. one way is 3 or more different people with different types. Understanding that we have micro organism millions of them on our bodies. Every animal does. And over time people and animals develop antibodies that protect them. but when we go to a different place, some people eating the same foods will get sick. Like when some people go to Mexico, and drink the water. Their relatives over 4 or more generations some got sick and died, and others built up antibodies that they passed on to their children. However, if one person has a virus that is harmless to them, and meets another person with a different virus also harmless to them, they share each others virus. Now if one of them meets a third person, with yet another virus, the 3 viruses can combine and make the 3rd person sick. Once they have the new 3 combo virus, that makes them sick, it now can be passed on to others. It is only called an STD if the major way to get it is to have sex. And it can even be more complicated. Although you might have heard aids came from monkeys. There is another theory that man made a disease, and they cure, did not work for all, and it mutated, to be able to transfer from monkeys to humans. Another theory is someone had a low immune system, and then was infected by the monkey aids, and then the low immune system mutated it to become apart of the new aids virus, that we have today. Another example is Europe grapes destroyed I think in the 60's. Someone brought over a California grape plant and it had an American bacteria that Paris grape plants could not fight off and they died. America had to reseed Paris' grape plants.

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I thinks AIDS came from monkeys, so uh... one down?