In July 2003, the Kittitas County Health Department and the Washington State Department of Health were notified of possible cases of tick-borne relapsing fever (TBRF) in 5 extended family members who stayed at a private rural cabin in Kittitas County. Three cases have been confirmed as TBRF by identification of Borrelia spirochetes on peripheral smear, and serological testing is pending on 2 others (one probable and one possible case). All ill persons have fully recovered and are residents of Washington State and British Columbia, Canada. All persons who visited the cabin recently have been notified. An environmental investigation of the cabin and the surrounding area is ongoing.

In the United States, relapsing fever is a tick-borne disease that typically occurs in the western states and is transmitted to humans by the bites of argasid tick species infected with the Borrelia spirochete from feeding on rodents and squirrels. These ticks typically feed only at night and do not remain attached like hard ticks do. They are found where rodents burrow and nest, and are difficult to eradicate. These ticks can survive for long periods between blood meals, and typically don't produce a noticeable bite. In the western United States and British Columbia, exposure to relapsing fever commonly occurs in older buildings and cabins located in higher elevations.

This disease is characterized by recurrent fevers of up to 105oF, lasting 2 to 9 days, followed by afebrile periods which last 2 to 4 days. The number of relapses can be 1 to 10, or greater. Other symptoms can include headache, chills, body aches, prostration, nausea and vomiting, and in some cases, a transitory petechial rash during the initial febrile period. Neurologic sequelae, such as aseptic meningitis and cranial nerve palsy, occur, but are rare. The incubation period is typically 8 days (range 4 to 18 days).

Relapsing fever is diagnosed by evidence of spirochetes in blood drawn during a febrile episode, bone marrow aspirates or cerebral spinal fluid. Relapsing fever is not spread person-to-person, although this infection can be acquired in utero.

Five cases have been reported in King County since 1998, one in 2000, and four in 2002. All cases had exposures outside of Washington State (suspected exposures occurred in Idaho, Montana and Oregon).

The 2002 King County cases were members of an extended family with exposures at an old cabin where extermination of rodents occurred just prior to exposure.

Persons with suspected or confirmed TBRF should be reported to Public Health for investigation of exposure and for identification of other exposed persons. Treatment of TBRF is with an appropriate antibiotic; prophylactic treatment is not recommended for asymptomatic persons who may have been exposed to TBRF-these persons should be monitored for fever for 18 days after last exposure.