Differentiation of endemic East African tick-borne relapsing
fever Borrelia duttonii spirochetes from epidemic
louse-borne relapsing fever (LBRF) B. recurrentis spirochetes
into different species has been questioned. We assessed
a noncoding intragenic spacer (IGS) region to compare
genotypes found in clinical samples from relapsing
fever patients. Although IGS typing was highly discriminatory
and resolved 4 East African tick-borne relapsing fever
groups from a disease-endemic region in Tanzania, 2 IGS
clades were found among LBRF patients in Ethiopia. The 2
IGS sequence types for B. recurrentis overlapped with 2 of
the 4 groups found among B. duttonii. All cultivable isolates
of B. duttonii fell into a single IGS cluster, which suggests
their analysis might introduce selective bias. We provide
further support that B. recurrentis is a subset of B. duttonii
and represents an ecotype rather than a species. These observations
have disease control implications and suggest
LBRF Borrelia spp. could reemerge from its tick-borne reservoirs
in which vectors coexist