1. a species that is a vector of Lyme disease (Borrelia burgdorferi) and human babesiosis (Babesia microti) in the U.S. Bites causing Lyme disease in humans are from nymphal ticks about the size of a pencil point, infected with B. burgdorferi from white-footed field mice. Adult ticks complete their 2-year life cycle feeding on deer. Also termed I. scapularis.
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