Outbreak of Tick-Borne Relapsing Fever in Spokane County, Washington

To our knowledge, the largest outbreak of tick-borne relapsing fever yet reported from the western hemisphere occurred in 1968 in Washington. Of 42 boy scouts and scoutmasters who camped out in March 1968 on Browne Mountain near Spokane, 11 contracted relapsing fever. Ten of 20 persons spending at least one night in old, rodent-infested cabins, and one of 22 scouts who tent-camped became ill. The diagnosis was based on the clinical manifestations, the epidemiological finding of high attack rates for persons sleeping in cabins, and the discovery of spirochetes in one patient's blood. Penicillins and tetracyclines used in treatment had no apparent effect on the course of the illness. Two of 18Ornithodoros hermsiticks collected from one cabin were shown to be infected with spirochetes. Preliminary laboratory experiments suggest that chipmunks and pine squirrels are the reservoir for the disease at Browne Mountain.