Really? I did not know that.
It does lend credence to the theory that some of these diseases entered the human population by way of people doing unspeakable things with animals ...
That theory was mentioned in my quick search. However, many STDs are spread through contaminated blood, and there are a lot of ways humans could come in contact with animal blood. Similarly, we usually think of Hepatitis-C as sexually-transmitted, but it can be spread in other conditions of very poor cleanliness, such as in day-care centers.