Characteristics of Hard Tick Relapsing Fever Caused by Borrelia miyamotoi, United States, 2013-2019

Abstract

Borrelia miyamotoi, transmitted by Ixodes spp. ticks, was recognized as an agent of hard tick relapsing fever in the United States in 2013. Nine state health departments in the Northeast and Midwest have conducted public health surveillance for this emerging condition by using a shared, working surveillance case definition. During 2013-2019, a total of 300 cases were identified through surveillance; 166 (55%) were classified as confirmed and 134 (45%) as possible. Median age of case-patients was 52 years (range 1-86 years); 52% were male. Most cases (70%) occurred during June-September, with a peak in August. Fever and headache were common symptoms; 28% of case-patients reported recurring fevers, 55% had arthralgia, and 16% had a rash. Thirteen percent of patients were hospitalized, and no deaths were reported. Ongoing surveillance will improve understanding of the incidence and clinical severity of this emerging disease.

Keywords: Borrelia miyamotoi; Ixodes scapularis; United States; bacteria; characteristics; emerging infectious diseases; hard tick relapsing fever; tick-borne infections; ticks; vector-borne infections; zoonoses.

Figure 1

US states that conducted surveillance for hard tick relapsing fever caused by Borrelia miyamotoi during 2013–2019 and year in which surveillance began.

Figure 2

Number of annual cases of hard tick relapsing fever (vertical bars) and number of states reporting cases of hard tick relapsing fever caused by Borrelia miyamotoi (line), United States, 2013–2019. The left y-axis corresponds to the vertical bars, and the right y-axis corresponds to the line; scales for the y-axes differ substantially to underscore patterns but do not permit direct comparisons. States reporting cases in that year are shown. CT, Connecticut; MA, Massachusetts; ME, Maine; MN, Minnesota; NH, New Hampshire; NJ, New Jersey; RI, Rhode Island; VT, Vermont; WI, Wisconsin.

Figure 3

Patient age distribution for confirmed (A) and possible (B) cases of hard tick relapsing fever caused by Borrelia miyamotoi identified by using public health surveillance, United States, 2013–2019.

Figure 4

Reported cases of hard tick relapsing fever caused by Borrelia miyamotoi by month of symptom onset, United States, 2013–2019. Solid line indicates total number of reported cases each month, and bars indicate number of confirmed (white) and possible (gray) cases each month.