Lyme Disease: The Ecology of a Complex SystemMost human diseases come from nature, from pathogens that live and breed in non human animals and are accidentally transmitted to us. Human illness is only the culmination of a complex series of interactions among species in their natural habitats. To avoid exposure to these pathogens, we must understand which species are involved, what regulates their abundance, and how they interact. Lyme disease affects the lives of millions of people in the US,