Colorado tick fever is an infection that is transmitted to humans by the bite of an infected tick.


Colorado tick fever is caused by the Colorado tick fever virus. Humans can get the virus through the bite of an infected tick. The Rocky Mountain wood tick is the principal carrier of the Colorado tick virus in the US, and its geographic range is confined to the western US states and areas above 5,000 ft. in elevation.

The virus is also carried by other small mammals, including ground squirrels, porcupines, and chipmunks. There have been reports of rare cases of Colorado tick fever caused by exposure in a laboratory setting and a blood transfusion.


Bug bites
Colorado tick fever is transmitted through the bite of an infected tick.
© 2009 Nucleus Medical Art, Inc.

Risk Factors

Living or traveling in mountain forest areas at altitudes above 5,000 feet in the Rocky Mountain region, especially between April and July, increases your chances of developing Colorado tick fever. If you have been in these areas, tell your doctor.


If you experience any of these symptoms do not assume it is caused by Colorado tick fever. These symptoms may be attributed to other, less serious health conditions. If you experience any one of them, see your physician. Symptoms usually appear 4-5 days after a tick bite occurs.

  • High fever
  • Chills
  • Severe headache
  • Pain behind the eyes
  • Sensitivity to light
  • Muscle pain
  • Lethargy
  • Abdominal pain
  • Vomiting
  • Nausea


Your doctor will ask about your symptoms and medical history, and perform a physical exam.

Tests may include the following:

  • Blood tests to identify the virus
  • Blood tests to identify antibodies for the virus
  • Other blood tests


There is no specific treatment for Colorado tick fever. Complications are extremely rare and include aseptic meningitis, encephalitis, and hemorrhagic fever. The fever and pain may be treated with acetaminophen (eg, Tylenol) and other pain relief medications. Once a person gets Colorado tick fever, it is believed that he or she will have immunity against re-infection.


To help reduce your chances of getting Colorado tick fever, take the following steps to limit your exposure to ticks:

  • Avoid tick-infested areas, especially during warmer months.
  • Wear light-colored clothing to better locate a crawling tick.
  • Tuck pants into socks when in tick-infested habitats.
  • Use tick repellents.
  • Regularly inspect and remove ticks from your body and your child’s body when in tick-infested habitats.
  • Remove ticks using fine-tipped tweezers by grasping the tick close to the skin’s surface and pulling upward steadily.
  • Disinfect tick bites with soap and water.