Molecular characterization of Borrelia spp. isolates from greater
metropolitan Chicago reveals the presence of Borrelia bissettii. Preliminary
report.

Picken RN, Picken MM
Loyola University Medical Center, Department of Pathology, Maywood, Illinois
60153

Lyme Disease in the US is concentrated in three endemic areas: the
Northeast, the upper mid-West, and the Pacific coast. In the mid-West, the
range of Lyme disease has expanded to include large parts of Wisconsin and
Minnesota. Despite its proximity to the mid-Western focus, Illinois, so far,
has not been considered an endemic area. However, more recent data suggest
that this situation may be changing. Also, the extent of borrelial diversity
in the mid-West remains largely unexplored. Here, we present preliminary
results on the molecular characterization of Borrelia isolates from rodents
captured in Cook and Lake Counties, both of which are parts of the greater
metropolitan Chicago area in Illinois. We investigated the rodent reservoir
present in forested areas of suburban Chicago in order to determine the
frequency of infection with the Lyme disease agent(s) by culture isolation
of Borrelia spirochetes (Picken et al., unpublished). Rodent isolates of
Borrelia were identified to the species level by genetic characterization.
In total, 19 isolates were obtained over 3 years from NW Cook Co. and Lake
Co. Pulsed-field gel electrophoretic analysis of Mlul digested DNA from
these isolates showed macrorestriction patterns similar to that of the
Californian isolate, strain DN127 (PF type I), New York isolate strain 25015
(PF type II), or a variant of the latter (PF type III). Sequence data
generated from the rrf(5S)-rrl(23S) intergenic spacer region of the
ribosomal RNA gene cluster confirmed the identity of all the Chicago
isolates studied to date as B. bissettii. These strains are unlike our
previous Borrelia isolates from NW Illinois and Wisconsin. In addition,
there was a pre{*filter*} association of B. bissettii infection with pratal
rodent species such as Microtus pennsylvanicus and Zapus hudsonius. The
relationship of this novel enzootic focus to the established mid-Western
endemic focus of Lyme disease remains to be elucidated. The geographic range
and reservoir diversity of this organism may have hitherto been
underestimated.