I'm not sure into which category to post this speculation, so I eventually plumped for "general"

The bible has the story of Sodom and Gomorrah, ancient cities condemned by god as practicing "evil and depraved" acts.
Could those acts have included bestiality?
Leda and the swan springs to mind.
Could this have resulted in a deadly virus infection?
To the populations of those days, with no knowledge of single celled organisms, let alone bacteria and viruses, the only explanation could be god's displeasure, and they would search for reasons to account for this displeasure.
Over the subsequent years the story would be further embellished to become the biblical tale.