Colorado tick fever, a relatively mild, self-limited arbovirus infection transmitted to humans by the bite of the wood tick Dermacentor andersoni. It is endemic in the mountainous regions above 5000 feet in the western United States and Canada and is most prevalent in the spring and summer months. The virus has been isolated from D. andersoni ticks in Alberta and British Columbia. It occurs most frequently in those with recreational or occupational exposure (hiking or fishing) in enzootic loci. Symptoms, which appear 3 to 6 days after the tick bite, occur in two phases separated by a period of remission and include chills, fever, and headache; pain in the eyes, legs, and back; and sensitivity to light. Treatment is supportive; analgesics can be given for headache and other pains. Also called American mountain fever, mountain fever, mountain tick fever. Compare Rocky Mountain spotted fever.
