Colorado tick fever (CTF) is a viral infection that develops after a bite from a Rocky Mountain wood tick.
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Formally recognized as a virus in 1946, CTF occurs mostly in people living in or visiting the western part of the United States (U.S.) and western Canada, according to the American Centers for Disease Control and Prevention.
Hundreds of cases of CTF are reported yearly in the U.S. The actual number of cases may be higher, as symptoms often go unrecognized, which means the condition remains undiagnosed.