SHORT REPORT - DENSITY OF LYME-DISEASE SPIROCHETES WITHIN DEER TICKS COLLECTED FROM ZOONOTIC SITES

We determined whether the density of Lyme disease spirochetes varied b etween individual host-seeking deer ticks. Guts were dissected from 30 adult Ixodes dammini collected from three intensely zoonotic coastal Massachusetts sites, and the number of Borrelia burgdorferi ri present was estimated by a modified counting technique using indirect immunof luorescence. A median of 1,925 spirochetes was observed; ticks from th e three sites contained similar numbers of spirochetes. No tick contai ned more than 4,500 spirochetes. Initial experimental reports establis hing the efficiency of spirochetal transmission may have been based on ticks with a uniform spirochetal density, and extrapolations from the se studies may thus overestimate the infectivity of host-seeking ticks in nature.