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Tick-Borne Diseases

Rocky Mtn Wood Tick
 Male (left) and female Rocky Mountain wood tick - Dermacentor andersoni 
Image provided by Mat Pound, USDA ARS, www.forestryimages.org


Colorado tick fever is the most common tick-borne disease in Colorado although most cases probably go unrecognized. Colorado tick fever is an acute viral illness characterized by fever, headache, body aches, nausea, abdominal pain, and lethargy. Typically, the illness lasts four to five days, followed by an apparent recovery, then a relapse of symptoms for two or three more days. Complete recovery ay take two to three weeks.  the disease is not life-threatening and infection results in life-long immunity. There is currently no preventative vaccine or effective treatment, except to let the disease run its course.


What causes Colorado Tick Fever?

Colorado tick fever is caused by a virus maintained in the environment in a rodent-tick-rodent cycle. The virus is transmitted to humans by the bite of an infected Rocky Mountain wood tick. Ticks begin to emerge in late February and March and seek for an animal host to take a blood meal which is necessary for their growth and reproduction.


The virus is transmitted to humans while an infected tick is obtaining a blood meal. Studies have shown that a tick must usually be attached for several hours to transmit enough virus to cause illness. If infected, a person will become ill in four to five days.


Rocky Mountain spotted fever is a serious disease that is transmitted by infected Rocky Mountain wood ticks. The initial symptoms, which follow an incubation period of 3 to 14 days, are "flu-like": there may be sudden onset of high fever, headache, chills, and muscle aches. A rash often appears a few days later. This rash spreads rapidly over the entire body and may even be seen on the palms of the hands and soles of the feet. Prompt medical attention is extremely important because Rocky Mountain spotted fever can be fatal if treatment is delayed. The illness can be cured with antibiotics.


What causes Rocky Mountain Spotted Fever?

Ticks can carry spotted fever organisms (rickettsia). Hungry ticks usually position themselves on grass or small bushes and wait for a potential host to pass by. If the tick drops onto a human's legs, it often crawls upward toward the head looking for a place to attach. Ordinarily infection takes place when disease-causing rickettsia are inoculated into the skin via the bite of a feeding tick. Quick removal of ticks is important because they often must be attached several hours before there is disease transmission. People who remove ticks from domestic animals can also become infected if they crush ticks between their fingers, causing rickettsia to penetrate the skin. Thus, whenever ticks are handled, it is important to wash hands immediately. The disease can occur year around.


How is Rocky Mountain Spotted Fever Diagnosed?

It is important to notify a physician if you become ill after an exposure to ticks. A diagnosis of Rocky Mountain spotted fever will be based on clinical signs and symptoms and is confirmed by positive laboratory test results.


Tree squirrels, chipmunks, and other wild rodents found in coniferous forests in the higher elevations of the Western United States serve as the primary reservoirs for the relapsing fever spirochete. The soft-bodied ticks (Ornithodoros sp.) that associate with these rodents can remain alive and infectious for years without feeding.


People with tick-borne relapsing fever suffer cyclical high fevers and other symptoms such as headaches and pain in the joints or muscles that easily can be mistaken for a severe flu. These episodes usually last several days, alternating with periods when the symptoms cease. In most patients, the infection responds to treatment with antibiotics. The disease is under recognized and underreported, and often mistaken for Lyme disease.


Human cases of illness tend to peak in the warmer months, but they can occur year-round. A tick population often becomes established with rodents that inhabit rustic mountain cabins. If the rodents die off, leave, or hibernate, the ticks look for other hosts. In winter, people will stay in these cabins and warm them up for a week. The rodents are not active, the ticks get warmed up, and they become hungry and start moving around looking for a food source. A person who's breathing is basically a carbon dioxide generator. The ticks actually orient to a carbon dioxide gradient, and this is one of the ways they find their hosts.