A febrile illness characterized by chills, aches, vomiting, leukopenia, and sometimes encephalitis. It is caused by the colorado tick fever virus, a reovirus transmitted by the tick Dermacentor andersoni. The disease is Monarch Disease Ontology term MONDO_0005708 (Colorado tick fever). Also known as: American mountain fever, Colorado tick encephalitis, Colorado tick fever virus caused disease or disorder, Colorado tick fever virus disease or disorder, Colorado tick fever virus infectious disease, Colorado tick-borne disease, Mountain fever, Mountain tick fever.