Transmission electron micrograph (TEM) of the Colorado tick fever virus (CTFV) (in green), a member of the genus Coltivirus, one of nine genera of the virus family known as the Reoviridae. Particles have a relatively smooth capsomeric surface structure, and icosahedral symmetry. Infection of humans with CTFV is characterized by abrupt onset of fever, chills, headache, retroorbital pain, photophobia, myalgia, abdominal pain, and generalized malaise. Severe forms of the disease that involve infection of the central nervous system (CNS) or hemorrhagic fever, pericarditis, myocarditis, and orchitis have been rarely observed, mainly in children.