The Yellow Pestilence - http://www.geocities.com/Athens/4725/files/welsh.html
"This life tells us that Shortly after Saint Teliavus had received the pastoral care of the Church of Llandaff, on account of a pestilence which nearly destroyed the whole nation he was obliged to leave Wales. It was called the Yellow Pestilence, because it made everyone it attacked yellow and bloodless; it appeared to men in the form of a column consisting of a watery cloud passing over the whole region. Everything living that it touched with its pestilential breath either died straightway or became sick unto death."
Seemingly this Yellow Pestilence appeared with some frequency; a vaporous cloud that floated gently down the valleys, descending on St David's and rained down on the populace. All who were touched by the cloud, or who breathed of it, were struck down by the yellow plague, becoming lethargic, sick and finally turning yellow before succumbing to death.
What if there was more to it than that...?
In a time when buboes herald the coming of death across the land, and villages close their boundaries to all outsiders, turn away those travellers trapped between settlements and rain arrows on messengers who may carry the black death between towns, the Yellow Pestilence strikes in the valleys.
The villagers sicken turning bright yellow in hue, and die, only to rise again as the Yellow Pestilence feeds them.
And then clings to them, carried by their dead steps to another village.
Maybe actually apply this story to modern times. The plague is unearthed by miners and only by researching old myths can the zombies be stopped. If there's time.