Borrelia burgdorferi, the Lyme disease agent in the gut of deer ticks. Ticks that feed on immunized 
mice show elimination of the spirochetes ( right), whereas ticks that feed on control mice contain 
numerous spirochetes (left). 
From Fikrig, E., Telford, S., Barthold, S.W., Kantor, F.S., Spielman, A., and Flavell, R.A. 1992. 
Proc Natl Acad Sci USA 89:5418-5421. 
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