A question about purified water got me to thinking about water-borne diseases which lead me to - History of emerging infectious diseases http://en.wikipedia.org/wiki/History_of_emerging_infectious_diseases http://en.wikipedia.org/wiki/Timeline_of_peptic_ulcer_disease_and_Helicobacter_pylori Marshall, Barry, "The discovery that Helicobacter pylori, a spiral bacterium, caused peptic ulcer disease", in Helicobacter Pioneers, pp. 165-202. Monique had a thread on the 2005 Nobel prize in Physiology and Medicine. Really fascinating stuff, and also worrisome because of emerging diseases given the mobility of the global economy. The US has seen invasive species, plant and animal, from other parts of the planet. I suppose this applies to pathogens too. It seems we've seem an increased frequency of tropical diseases, e.g. W. Nile virus.