Tickborne Relapsing Fever, Bitterroot Valley, Montana, USA

In July 2013, a resident of the Bitterroot Valley in western Montana, USA, contracted tickborne relapsing fever caused by an infection with the spirochete Borrelia hermsii. The patient’s travel history and activities before onset of illness indicated a possible exposure on his residential property on the eastern side of the valley. An onsite investigation of the potential exposure site found the vector, Ornithodoros hermsi ticks, and 1 chipmunk infected with spirochetes, which on the basis of multilocus sequence typing were identical to the spirochete isolated from the patient. Field studies in other locations found additional serologic evidence and an infected tick that demonstrated a wider distribution of spirochetes circulating among the small mammal populations. Our study demonstrates that this area of Montana represents a previously unrecognized focus of relapsing fever and poses a risk for persons of acquiring this tickborne disease

A Novel Surface Antigen of Relapsing Fever Spirochetes Can Discriminate between Relapsing Fever and Lyme Borreliosis▿ † ‡

In a previous immunoproteome analysis of Borrelia hermsii, candidate antigens that bound IgM antibodies from mice and patients infected with relapsing fever spirochetes were identified. One candidate that was identified is a hypothetical protein with a molecular mass of 57 kDa that we have designated Borrelia immunogenic protein A (BipA). This protein was further investigated as a potential diagnostic antigen for B. hermsii given that it is absent from the Borrelia burgdorferi genome. The bipA locus was amplified and sequenced from 39 isolates of B. hermsii that had been acquired from western North America. bipA was also expressed as a recombinant fusion protein. Serum samples from mice and patients infected with B. hermsii or B. burgdorferi were used to confirm the immunogenicity of the recombinant protein in patients infected with relapsing fever spirochetes. Lastly, in silico and experimental analysis indicated that BipA is a surface-exposed lipoprotein in B. hermsii. These findings enhance the capabilities of diagnosing infection with relapsing fever spirochetes

Endemic Foci of the Tick-Borne Relapsing Fever Spirochete <em>Borrelia crocidurae</em> in Mali, West Africa, and the Potential for Human Infection

<div><h3>Background</h3><p>Tick-borne relapsing fever spirochetes are maintained in endemic foci that involve a diversity of small mammals and argasid ticks in the genus <em>Ornithodoros</em>. Most epidemiological studies of tick-borne relapsing fever in West Africa caused by <em>Borrelia crocidurae</em> have been conducted in Senegal. The risk for humans to acquire relapsing fever in Mali is uncertain, as only a few human cases have been identified. Given the high incidence of malaria in Mali, and the potential to confuse the clinical diagnosis of these two diseases, we initiated studies to determine if there were endemic foci of relapsing fever spirochetes that could pose a risk for human infection.</p> <h3>Methodology/Principal Findings</h3><p>We investigated 20 villages across southern Mali for the presence of relapsing fever spirochetes. Small mammals were captured, thin blood smears were examined microscopically for spirochetes, and serum samples were tested for antibodies to relapsing fever spirochetes. <em>Ornithodoros sonrai</em> ticks were collected and examined for spirochetal infection. In total, 11.0% of the 663 rodents and 14.3% of the 63 shrews tested were seropositive and 2.2% of the animals had active spirochete infections when captured. In the Bandiagara region, the prevalence of infection was higher with 35% of the animals seropositive and 10% infected. Here also <em>Ornithodoros sonrai</em> were abundant and 17.3% of 278 individual ticks tested were infected with <em>Borrelia crocidurae</em>. Fifteen isolates of <em>B. crocidurae</em> were established and characterized by multi-locus sequence typing.</p> <h3>Conclusions/Significance</h3><p>The potential for human tick-borne relapsing fever exists in many areas of southern Mali.</p> </div

Genomic groups, sequence types and plasmid types for 15 isolates of <i>Borrelia crocidurae</i> from Doucombo and Kalibombo, Mali.

a<p>X; the concatenated sequence for this isolate included in <a href="http://www.plosntds.org/article/info:doi/10.1371/journal.pntd.0001924#pntd-0001924-g006" target="_blank">Figure 6</a>.</p

Phylogram based on the concatenated DNA sequences of the 16S rDNA, <i>flaB</i> and <i>glpQ</i> loci.

<p>The Malian isolates, represented by the six unique sequence types, group with <i>Borrelia crocidurae</i> from Mauritania (Achema). Scale bar represents the number of base substitutions per nucleotide.</p

The number of mammals captured at each village, the number of serological tests performed, and the number and percent of animals seropositive.

<p>The number of mammals captured at each village, the number of serological tests performed, and the number and percent of animals seropositive.</p

Villages sampled, their administrative district and number, and geographic coordinates.

<p>Villages sampled, their administrative district and number, and geographic coordinates.</p

The species and number of small mammals captured in Mali.

<p>The species and number of small mammals captured in Mali.</p

Map of Mali with the names and locations of the 20 villages investigated.

<p>The location of Mali in the African continent is identified in grey.</p

Agarose gel showing plasmid content of 15 isolates of <i>Borrelia crocidurae</i> from Mali.

<p>The isolate designations are shown above with the genomic groups determined by MLST analysis (genomic groups A–D). Stars on right are aligned with presumptive circular plasmids identified in 2-dimensional agarose gels (not shown). The plasmid types (I–VI) are on the bottom. Molecular size standards (MSS) are shown on left in base pairs.</p