Tickborne Relapsing Fever

Stephen G. Baum, MD reviewing Jones JM et al. MMWR Morb Mortal Wkly Rep 2015 Jun 19.

An outbreak of tickborne relapsing fever in Arizona had a 24% attack rate in a group of 45 campers.

In North America, tickborne relapsing fever (TBRF) is most commonly caused by Borrelia hermsii spirochetes that are transmitted from rodent reservoirs to humans by Ornithodoros hermsii ticks during 15- to 90-minute feeds. The infection is characterized by recurrent episodes of fever, myalgia, arthralgia, headache, and nausea after an incubation period of several days. Between 1982 and 2013, the number of cases reported in Arizona each year was zero to three.

On August 10, 2014, Arizona health officials were notified by a hospital that five high school students who had attended an outdoor educational camp had been admitted for fever, headache, and myalgias. Although Hantavirus infection was suspected, blood smears from all five patients revealed spirochetes, leading to a diagnosis of TBRF. A sixth case was subsequently confirmed, and five probable cases were diagnosed on the basis of attendance at the same camp and the onset of TBRF signs and symptoms. The average incubation period for the entire group was 6 days (range, 2–10 days). All six patients with confirmed TBRF exhibited fever, headache, myalgias, and arthralgias; five of them also had thrombocytopenia. Eight of the 11 patients were treated with doxycycline, with no reports of major complications.

Evidence of rodents and the tick vector were found in the camp's main cabin.

Citation(s):

Jones JM et al. Tickborne relapsing fever outbreak at an outdoor education camp — Arizona, 2014. MMWR Morb Mortal Wkly Rep 2015 Jun 19; 64:651.