Howdy, sorry I don't have the original posting for who started this thread. What I remember is a conversation with someone who had done agricultural research in India, namely the study of nematodes, and specifically, the study of hookworms. What he found was that to keep the incidence of hookworms down in people (which could be absorbed through the skin, when in contact with infected fecal matter) was the practice of keeping a 'zone' around each dwelling where no one was to relieve him or herself. This 'zone' was only violated by the very old, the very young, or the very sick. Perhaps what you may need to look at are pests or diseases native to the areas from which the individuals came from. Joanne Reiter