Colorado tick fever (CTF) is a viral infection that can be transmitted from an infected Rocky Mountain wood tick bite. Also known as mountain tick fever, this disease occurs primarily in mountainous areas of Canada and the Western United States. Initial symptoms are similar to those of many diseases, but are generally followed by a secondary phase of high fever. There is no treatment for this disease, and up to 20% of those infected may need to be hospitalized.
The virus that causes Colorado tick fever lives in red blood cells, both in humans and in the blood in infected ticks. When ticks that are infected with this virus attach to a human, the resulting tick bite can transmit the infection. It can take up to four hours to transmit the virus. If the tick is removed before this time, it may be possible to preempt transmission. The virus is not transmitted between people.
Colorado tick fever is only transmitted during certain seasons. Most of the cases occur from April to July, in forests, at altitudes from 4,000 to 10,000 ft (1,220-3,050 m). The largest number of cases is usually reported in Colorado. Most of the people infected are typically camping enthusiasts or those who work in a forest.
Diagnosis is difficult since the initial symptoms resemble those of many other diseases. It is thought that the number of Colorado tick fever cases is greatly under-reported. There are often two stages of fever and sickness following the bite of an infected tick.
The average period of incubation before symptoms develop is four days, although this period can range from one to 19 days. The early signs of infection include a sudden fever with headache, chills, sensitivity to light, pain behind the eyes, and muscle pain. There may also be nausea and vomiting, along with abdominal pain. A small percentage of people will develop a rash. This first phase generally lasts for two to three days.
After this, there is normally a period of one to three days of malaise and anorexia, but no fever. The fever often returns for the second phase, along with an increase in the other symptoms. This second period lasts for about two additional days. The key diagnostic features are the fever and a recent bite by a tick. While many people recover on their own, Colorado tick fever can be a serious illness for young children and the elderly.
Diagnosis is based on a combination of symptoms and laboratory tests. There are antibodies to assay for the presence of the virus, and cell culture systems to grow the virus to confirm its presence. There is no treatment for Colorado tick fever, except for rest and painkillers to relieve symptoms. Affected children should not be given aspirin, however, particularly in combination with a viral infection, since this may trigger Reyes syndrome. Aspirin derivatives called salicylates should also not be used as painkillers, since they may cause serious complications.