Vector-associated illnesses are increasing in frequency across the United States (1). Compared with more common vectorborne illnesses such as Lyme borreliosis, Rocky Mountain spotted fever, tularemia, babesiosis, anaplasmosis, and ehrlichiosis, far less is known about TBRF, so much so that it has been described as a neglected disease (2).

TBRF typically manifests after a 7-day incubation period with recurring episodes of fever in association with headache, myalgias, and other nonspecific symptoms lasting for ≈3 days and separated by afebrile periods of ≈7 days’ duration. In the United States, B. hermsii is thought to be the most common cause of TBRF, and transmission is associated with the bite of soft O. hermsi ticks. Ornithodoros spp. ticks usually feed at night on rodents, such as tree squirrels and chipmunks, but might choose to feed on human hosts, particularly when the rodent population has been cleared from the local habitat. Feeding is rapid, and most persons who are bitten are not aware of a tick bite. Cabins are a typical site to acquire infection. In addition, soft ticks can live up to 10 years; this long lifespan means that once a cabin or building is infested, it can remain a source of human infection for years unless steps are taken to find and remove rodent infestations and eradicate the ticks. The risk for reinfection for any 1 person has not been calculated; however, repeated exposures, especially at the same sites as initial infection, are possible (3).

The 6 cases we describe occurred among persons inhabiting cabins in the White Mountains of Arizona during the late spring to early fall months. All but 1 person sought care with recurrent fever as their primary complaint; some had profound laboratory abnormalities, including leukopenia, thrombocytopenia, hyperbilirubinemia, and elevated aminotransaminases. One patient had organ-specific disease (uveitis). All case-patients responded promptly to doxycycline therapy; 2 had Jarisch-Herxheimer reactions in association with antimicrobial therapy, a phenomenon previously described (4). Two case-patients had positive serologic results for coccidioidomycosis, which were likely coincidental, given the relatively high incidence of this fungal infection in the desert regions of Arizona (5). The positive tests for Lyme borreliosis were likely attributable to cross-reactivity, as has been previously noted (6).

Figure 2

Figure 2. Exposure location for historic (1973–2014) tickborne relapsing fever outbreaks in Coconino County and 6 current (2013–2018) cases in the White Mountains region, Arizona, USA.

TBRF in Arizona has been described in the past around or near the Grand Canyon (7–9), several hundred miles from the site of these 6 cases (Figure 2). Apache County, the location of the 2013–2018 cases we have described, has been considered to be a comparatively low-incidence area for TBRF (3).

Unfortunately, no epidemiologic or environmental assessments were performed in these 6 cases. Although the benefits of conducting such studies are recognized, these studies were not performed here primarily because the cases were episodic. Limited resources of the local public health jurisdictions and lack of compliance from cabin owners also contributed. If future cases occur, such assessments would be useful to define whether B. hermsii is indeed the cause of the syndromes observed and to better define the ecologic, environmental, and epidemiologic parameters of the disease.

In Arizona, TBRF is a reportable disease by physicians to the local health department according to 2018 Arizona statutes (AR9-6-202). Although TBRF is not a nationally notifiable condition, prompt reporting of TBRF cases was required in >12 states in 2016 (Arizona, California, Colorado, Idaho, Montana, North Dakota, Nevada, New Mexico, Oregon, Texas, Utah, and Washington). Because of frequent travel by US residents, healthcare providers should report cases to the appropriate state or local health department; prompt reporting by clinicians has been critical to the identification and control of several outbreaks. For example, in 2014, a local Arizona hospital notified the Coconino County Public Health Services District (Flagstaff) of a cluster of 5 students with fever, headache, and myalgia who had attended the same camp; the ensuing investigation led to identification of an outbreak of 10 cases of TBRF among a high school football team who had attended an outdoor education camping trip in northern Arizona (9).

The first case of TBRF in Arizona was reported in 1930, involving an exposure near Greer, similar to the 6 cases we have described. In that instance, after staying in the area for 18 days during the summer, a 37-year-old man had repeated bouts of fever with interval periods of well-being lasting several days. During 1 febrile attack, which occurred >1 month after symptoms began, a blood smear demonstrated spirochetes. The patient received an arsenial injection, and his fevers resolved (10).

Far more cases of TBRF probably have occurred recently in the White Mountains than the 6 reported here. Unlike previous recent reports from other parts of Arizona (7–9), the cases we report were not epidemic and therefore could have been easily missed. Therefore, physicians practicing in areas that serve this region should be aware of TBRF and consider the diagnosis when a patient has a nonspecific febrile illness, particularly when that illness is recurrent. In addition, all healthcare providers should assess travel history in patients who have nonspecific febrile illnesses and should consider diseases related to specific travel exposures. In addition to being able to recognize TBRF, healthcare providers in Arizona should be vigilant for other zoonotic diseases that could result from local exposures, such as hantavirus from deer mice, plague from fleas and prairie dogs, and Rocky Mountain spotted fever transmitted from brown dog ticks.