Coltivirus (‘Colti’ from Colorado tick fever (CTF)) (family Reoviridae ) is a genus of viruses that consist of 12 segments of double‐stranded ribonucleic acid (dsRNA). CTF is the most important tick‐borne human pathogen in the United States of America. Human infections occur after the bite of Colorado tick fever virus (CTFV)‐infected adult ticks, mainly Dermacentor spp. First described by Becker in 1930, at least 22 strains of CTFV are known, many of which cause disease in humans.

Coltivirus (‘Colti’ from Colorado tick fever (CTF)) (family Reoviridae ) is a genus of viruses that consist of 12 segments of double‐stranded ribonucleic acid (dsRNA) . CTF is the most important tick‐borne human pathogen occurring in the mountain forest habitats at altitudes from 4000 to 10 000 ft in the Rocky Mountain region of the USA. Human infections are caused by the bite of Colorado tick fever virus (CTFV)‐infected adult ticks, mainly Dermacentor spp., with a 90% occurrence rate during the months of April to July. First described by Becker in 1930, at least 22 strains of CTFV are known, many of which cause disease in humans. The disease is easily confused with other infections, and is extensively underreported. The European Eyach virus, isolated in Germany and France, is the second species in the genus Coltivirus. Salmon River virus is considered a tentative species. Key Concepts: CTFV is the most important tick‐borne human pathogen in the USA, especially in the Rocky Mountain region. Coltiviruses are considered ‘emerging infections’ owing to their high frequency in RNA segment reassortments, both in tissue cultures and in tick vectors. Clinical features of CTFV infections in humans are consistent with pathological changes observed in animals. There is no specific treatment for human coltivirus infections. Antiviral agents, ribavirin and 3‐deazauridine significantly inhibit the growth of CTFV in vitro and ribavirin administered to mice intraperitoneally protected them against intracerebral challenge with CTFV. Coltivirus particles are nonenveloped, approximately 80 nm in diameter and consist of two capsid layers, with icosahedral symmetry, that appear smooth. Each virion contains a full‐length copy of 12 segments of linear, double‐stranded, positive‐sense RNA. Coltiviruses are sensitive to low pH and anionic detergents, such as sodium deoxycholate, both of which abolish virus infectivity. Mycoreoviruses recently isolated from fungi may be used to reduce virulence of fungi as biocontrol agents. Seadornaviruses may not be correctly classified within the genus Coltivirus mainly due to low amino acid similarity differences in their invertebrate vectors and their geographical distributions. There is an evolutionary link between the 11‐segmented aquareoviruses and the 12‐segmented coltiviruses.