Dear Bingley: thanks for the link. I read it with great interest, because the writer had so much good sense, and was a good observer. There was no mention of rats or their fleas.The spread apparently did not run the course I read about years ago, with earliest cases having buboes with slow progression of the disease, and later cases being pneumonic with rapid spread and quick death. Hard to explain the erratic spread, with some escaping infection for a couple months.