Quantitative Real-time PCR in Borrelia Persica Tick-Borne Relapsing Fever demonstrates correlation with the Jarisch-Herxheimer Reaction

Purpose: Tick-borne relapsing fever (TBRF) in Israel is caused by the spirochete Borrelia persica. As in other diseases caused by spirochetal bacteria, the initiation of treatment in TBRF often leads to a systemic reaction, called the Jarisch Herxheimer reaction (JHR). The purpose of this study is to explore whether a correlation exists between the bacterial load of B. persica in TBRF, established by quantitative real-time PCR (RT-PCR), and the development of JHR after the initiation of antibiotic treatment.

Methods: Blood samples of patients discharged with a diagnosis of TBRF between 2009 and 2019 were stored for clinical purposes. The quantitative test of bacterial DNA was done by quantitative RT-PCR from these samples.

Results: Forty two patients diagnosed with TBRF were included in our study. Thirteen patients (31%) developed clinical JHR while being observed in the emergency department after the initiation of antibiotic treatment. The mean bacterial load, as established by RT-PCR, in patients who developed JHR was significantly greater than in those patients who did not develop JHR (443,293 copies vs. 140,598, p=0.035). Additionally, a positive thin blood smear also indicated a significantly elevated risk of developing JHR (odds ratio 5.72 [95% confidence interval 1.02-32.1], p=0.047).

Conclusions: A significant correlation was found between a greater bacterial load of B. persica, as indicated by the number of copies by RT-PCR, and the risk of developing JHR. Accordingly, positive blood smears, as well as RT-PCR, may assist clinicians in identifying patients at higher risk of JHR who require closer monitoring before discharge.