Colorado tick fever

Colorado tick fever, acute febrile viral infection usually transmitted to humans by the bite of the Rocky Mountain wood tick (Dermacentor andersoni). The virus, known as the Colorado tick fever virus, is classified as a type of coltivirus of the family Reoviridae, a grouping of viruses that is characterized by the lack of a lipid envelope and the presence of two protein coats.

D. andersoni requires a vertebrate host for part of its life cycle. The main mammalian reservoirs of the virus include chipmunks, mice, and squirrels. Ticks acquire the virus while feeding on the blood of a reservoir host. A tick then passes the virus to another animal or to a human when it feeds again. The carrier tick is found chiefly in the western parts of the United States, notably in Colorado, and is most active in late spring and summer.

A few days following tick exposure, the fever onset is abrupt, often with intolerance to light, headache, and prostrating weakness. Aching soon becomes generalized, especially in the muscles and joints. Abdominal pain and vomiting occur occasionally. The first attack lasts about two days. After a complete remission of all signs and symptoms lasting also about two days, there is in most cases a second attack that may be even more acute than the first.

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There are no specific treatments for Colorado tick fever. Except for the rare development of brain inflammation (encephalitis) in young children, recovery is usually uncomplicated, and there is lifelong immunity.