Coltivirus is a genus of viruses (belonging to the Reoviridae family) that infects vertebrates, invertebrates, and plants. It includes the causative agent of Colorado tick fever. Colorado tick fever virus can cause a fever, chills, headache, photophobia, myalgia, arthralgia, and lethargy. Children, in particular, may develop a hemorrhagic disease. Leukopenia with both lymphocytes and neutrophils is very common for Colorado tick fever virus. In either case, the infection can lead to encephalitis or meningitis.