Colorado tick fever virus (CTFV) is a double‑stranded RNA virus of the genus Coltivirus (family Reoviridae). Its genome consists of twelve segments and it has an icosahedral capsid about 80 nm in diameter. The virus infects red blood cells of vertebrate hosts and is transmitted primarily by the Rocky Mountain wood tick (Dermacentor andersoni).
Transmission, hosts and clinical features
Infection is acquired by bites from infected ticks at elevations between 1 200 and 3 000 m in western North America. The virus circulates in small rodents, including ground squirrels, chipmunks and deer mice, which act as amplifying hosts. Humans are incidental hosts and do not transmit the virus to others; rare cases of transmission have occurred through blood transfusion or perinatal exposure. After an incubation period of 1–14 days, patients develop sudden fever, chills, headache, myalgia and fatigue. About half of cases follow a biphasic pattern with a recurrence of fever after a brief remission. Some patients have sore throat, abdominal pain or vomiting, and laboratory findings often reveal leukopenia and thrombocytopenia. The illness is typically self‑limited and most people recover completely within two weeks, although fatigue can persist for several weeks. Severe complications such as meningitis or hemorrhagic manifestations are uncommon. No specific antiviral therapy or vaccine exists; management is supportive.
Key studies and public health notes
Notable studies have shown that Colorado tick fever virus remains in red blood cells for months, prompting recommendations that infected individuals should defer blood donation for at least six months. Surveillance data indicate that cases cluster in mountainous regions of Colorado, Wyoming, Utah, Idaho and Montana, with infections peaking in late spring and early summer when adult ticks are active. The virus was first recognized in the 1940s and has since been isolated from both tick vectors and rodent reservoirs. Molecular diagnostics, including reverse‑transcription PCR, are used for confirmation alongside serologic tests. Public health campaigns emphasize tick avoidance measures such as wearing long sleeves, using repellents containing DEET and promptly removing attached ticks. Because the virus can co‑infect cells with other pathogens carried by Dermacentor ticks, clinicians should consider co‑infection with bacterial agents like Rickettsia or Anaplasma when evaluating febrile travellers returning from endemic areas.
Colorado tick fever virus is an arthropod‑borne coltivirus maintained in a sylvatic cycle involving wood ticks and rodents in the western United States and Canada. Human infections are typically mild but can cause prolonged fatigue and require exclusion from blood donation. Preventive measures aimed at reducing tick exposure remain the cornerstone of control.
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