Insights into Borrelia miyamotoi infection from an untreated case demonstrating relapsing fever, monocytosis and a positive C6 Lyme serology

•Borrelia miyamotoi is a relapsing fever borrelia transmitted by Ixodes spp. ticks.•We describe a patient with B. miyamotoi infection who recovered without antibiotics.•The patient had 2 episodes of fever 3 weeks apart, each episode ≤5 days in duration.•The patient demonstrated blood monocytosis and reactivity to the C6 peptide of B. burgdorferi.•Seroreactivity to the C6 peptide was also demonstrated in B. hermsii and B. turicatae infections.

We describe a patient from the United States with PCR- and serology-confirmed Borrelia miyamotoi infection who recovered without antibiotics. Our findings suggest that B. miyamotoi infection may cause relapsing fever, blood monocytosis and antibody reactivity to the C6 peptide. Further studies are required to better define the spectrum of clinical and laboratory findings for this emerging tick-transmitted infection.