After watching almost 5 seasons of The Walking Dead I expected that some of the mystery gets be revealed about "authors" of the virus and how it spread, but apparently the producers are not going to do that unless it happend in season 6. Are they going to reveal how the virus spread and who made it?
Quite possibly no.
"[Learning the origins] is not the priority in Walking Dead; that's not the priority in Fear The Walking Dead," Kirkman told a packed panel at the NAB Show in Las Vegas. "Every other story deals with that stuff and we're concerned about the heart."
He then went on to say:
"I know the story, but I've never bothered to write it down," he said. "Let's hope I don't die."
So he knows how the zombie outbreak started, but he never considered it interesting enough to be the main focus of the show.
Given this, it's possible we'll never have the reasons revealed - it's impossible to tell right now.