Phylogenetic Analysis of the Spirochete Borrelia microti, a Potential Agent of Relapsing Fever in Iran

Abstract

We report a role for Borrelia microti as a cause of relapsing fever in Iran supported by robust epidemiological evidence. The molecular identity of this spirochete and its relation with other relapsing fever borreliae have, until now, been poorly delineated. We analyzed an isolate of B. microti , obtained from Ornithodoros erraticus ticks, by sequencing four loci (16S rRNA, flaB , glpQ , intragenic spacer [IGS]) and comparing these sequences with those of other relapsing fever borreliae. Phylogenetic analysis using concatenated sequences of 16S rRNA, flaB , and glpQ grouped B. microti alongside three members of the African group, B. duttonii , B. recurrentis , and B. crocidurae , which are distinct from B. persica , the most prevalent established cause of tick-borne relapsing fever in Iran. The similarity values for 10 concatenated sequences totaling 2,437 nucleotides ranged from 92.11% to 99.84%, with the highest homologies being between B. duttonii and B. microti and between B. duttonii and B. recurrentis . Furthermore, the more discriminatory IGS sequence analysis corroborated the close similarity (97.76% to 99.56%) between B. microti and B. duttonii . These findings raise the possibility that both species may indeed be the same and further dispel the one-species, one-vector theory that has been the basis for classification of relapsing fever Borrelia for the last 100 years.

Ornithodoros savignyi, the Tick Vector of “Candidatus Borrelia kalaharica” in Nigeria

“…Conversely, human infection can serve as a sentinel for detection of novel species. Indeed, this was recently the case for detection of a novel TBRF species endemic to Iran (8,9) and, more recently, with the report of a new TBRF species, "Candidatus Borrelia kalaharica," in a tourist returning from a holiday in southern Africa (10). This patient from Germany had clinical signs compatible with relapsing fever, and raised clinical awareness in this region, probably through recent introductions of LBRF among the influx of African refugees into Germany (11,12), potentially aided diagnosis.…”

Division of the genus Borrelia into two genera (corresponding to Lyme disease and relapsing fever groups) reflects their genetic and phenotypic distinctiveness and will lead to a better understanding of these two groups of microbes (Margos et al. (2016) There is inadequate evidence to support the division of the genus Borrelia. Int. J. Syst. Evol. Microbiol. doi: 10.1099/ijsem.0.001717)

“…These include B. recurrentis [57,59], B. hermsii [63,64], B. microti [59,65] and B. persica [66]. B. recurrentis was reported to have eight flagella at each end, but the insertion points are not well visualized in the figure that was provided [67].…”

Relapsing fever causative agent in Southern Iran is a closely related species to East African borreliae

“…microti is scarce and confined to one strain from the center of Iran (Naddaf et al, 2012). There are chances that in the south of Iran O. erraticus ticks or similar species serve as a host and vector of closely related Borrelia species or ecotypes including the one we identified in the present study.…”

“…This spirochete was only isolated once and attempts to maintain it in laboratory animals failed; no tick vector has been identified for this species to date (Karimi et al, 1979, Karimi, 1981. Molecular characterization of B. persica from Iran has been reported (Ras et al, 1996, Shirani et al, 2016 (Naddaf et al, 2012). Similarly, 16S-23S intragenic sequence (IGS) analysis conducted in situ using blood from relapsing fever patients in Hormozgan Province, southern Iran showed greatest similarity with East African relapsing fever borreliae, B. recurrentis and B. duttonii, but was surprisingly distinct from B. microti transmitted by O. erraticus ticks, previously believed to be the only soft tick species in this region (Naddaf et al, 2015).…”