Sequence analysis and serological responses against Borrelia turicatae BipA, a putative species-specific antigen.

BACKGROUND: Relapsing fever spirochetes are global yet neglected pathogens causing recurrent febrile episodes, chills, nausea, vomiting, and pregnancy complications. Given these nonspecific clinical manifestations, improving diagnostic assays for relapsing fever spirochetes will allow for identification of endemic foci and expedite proper treatment. Previously, an antigen designated the Borrelia immunogenic protein A (BipA) was identified in the North American species Borrelia hermsii. Thus far, BipA appears unique to relapsing fever spirochetes. The antigen remains unidentified outside of these pathogens, while interspecies amino acid identity for BipA in relapsing fever spirochetes is only 24-36%. The current study investigated the immunogenicity of BipA in Borrelia turicatae, a species distributed in the southern United States and Latin America. METHODOLOGY/PRINCIPAL FINDINGS: bipA was amplified from six isolates of Borrelia turicatae, and sequence analysis demonstrated that the gene is conserved among isolates. A tick transmission system was developed for B. turicatae in mice and a canine, two likely vertebrate hosts, which enabled the evaluation of serological responses against recombinant BipA (rBipA). These studies indicated that BipA is antigenic in both animal systems after infection by tick bite, yet serum antibodies failed to bind to B. hermsii rBipA at a detectable level. Moreover, mice continued to generate an antibody response against BipA one year after the initial infection, further demonstrating the protein's potential toward identifying endemic foci for B. turicatae. CONCLUSIONS/SIGNIFICANCE: These initial studies support the hypothesis that BipA is a spirochete antigen unique to a relapsing fever Borrelia species, and could be used to improve efforts for identifying B. turicatae endemic regions

Oligonucleotides and quantitative PCR probe.

<p>Oligonucleotides and quantitative PCR probe.</p

Serological responses from mice infected with TCB-1 (A and B) and FCB-1 (C and D).

<p><i>B. turicatae</i> protein lysates and rBipA produced from the 91E135 isolate are shown. Molecular masses are indicated to the left of each immunoblot in kilodaltons.</p

Long-term serological responses from four mice one year after tick bite (A–D).

<p><i>B. turicatae</i> protein lysates and rBipA produced from the 91E135 isolate and <i>B. hermsii</i> are shown. Molecular masses are indicated to the left of each immunoblot in kilodaltons.</p

Canine temperature and platelet counts during infection.

A<p>Values are based on automated platelet counts. Reference range was from 160,000 to 650,000. Automated platelet counts were noted on days 9 and 13, when counts were below normal.</p>B<p>Baseline temperature and platelet counts were taken prior to transmission by tick bite.</p>C<p>Spirochetemic episode.</p

Amino acid alignments of <i>B. turicatae</i> BipA from six isolates.

<p>Identical amino acids are shaded grey.</p