WMS Blog Entry No. 4, Part II: Tick Lifecycle and Diseases in Colorado

There are two types of ticks in Colorado: soft and hard. Hard ticks have a plate on the back of their head like armor and mouth parts that are visible and directed forward. Hard ticks are differentiated by soft ticks how? You guessed it: Soft ticks do NOT have that plate on their head and their mouthparts are not visible because they lie beneath the tick.

Ticks have 4 stages of life: Adult ticks lay thousands of 1) eggs which hatch as 2) 6-legged tiny larva which develop and mold into 3) 8-legged young adult nymphs. After eating and developing yet again, the nymphs turn into 4) adults. Depending on tick type, the larvae, nymph, and adult ticks can be active and feed on blood. While ticks in most of the country develop over 1 year, ticks commonly encountered in Colorado usually require 2-3 years to develop.

While there are 27 species of ticks in Colorado, the two seen with most prevalence are the Rocky Mountain wood tick and the brown dog tick. Almost all human encounters with ticks here involve the Rocky Mountain wood tick, as this tick resides in the western U.S. and southern Canada at elevations between 4,000 and 10,000 feet.

Tick sensing its host! Courtesy of Tick-Borne Disease WMS Presentation

The adult Rocky Mountain wood tick feeds on larger mammals and humans and can carry the bacteria that cause RMSF, Colorado tick fever and tularemia. The adult tick climbs onto vegetation and waits ever so patiently until it detects vibrations, exhaled carbon dioxide, and warmth that passing mammals give off.

Adult Female and Male Rocky Mountain wood tick, photo courtesy of Colorado Ticks fact sheet

Brown dog ticks are found at lower elevations and warmer areas, and seem to only develop on dogs. Not surprisingly, these ticks are found in areas where dogs are kept in close quarters, such as kennels and homes.

Fun Fact: Most hard ticks are 3-host ticks, meaning they feed from one host and then drop from that host after each feeding (blood meal) to develop into the next stage.

Not so fun fact: Hard ticks can survive a whole year without feeding! These ticks also become dormant with high temperatures in late spring and summer, meaning they are most active in the spring. On the other side of the spectrum, soft ticks feed more briefly and frequently than hard ticks, feeding several times before they develop into the next stage.

Tick Borne Diseases:

The most common tick-spread disease in Colorado is Colorado Tick Fever with around 200 cases reported in Colorado per year. This disease is caused by a virus and is carried by the Rocky Mountain wood tick. Those infected may experience headache, fever, chills and fatigue that occur 1-14 days after the tick bite. Special to this disease is that symptoms are biphasic, meaning you will get very sick for a couple of days, then feel better (recovery phase), then become sick again. Since this disease is viral in origin, treatment is supportive, meaning medication is given to decrease your symptoms such as headache and fever.

Despite its name, Rocky Mountain spotted fever is a rarely diagnosed disease in Colorado, with around 3 reported cases per year. This serious and potentially life-threatening disease caused by the bacteria Rickettsia rickettseii is carried by both the Rocky Mountain wood tick and Brown dog tick, and has higher prevalence along the east coast in states such as North and South Carolina. This bacterium can spread from tick to human in only 6-10 hours of the tick being attached, a relatively short exposure time when compared to other tick borne diseases such as Lyme disease, which requires around 36 hours of attachment in order to spread. Early symptoms can appear within 3-12 days after tick contact and include headache, fever, upset stomach and myalgia (muscle aches). A notorious rash on the palms of the hands and soles of the feet may appear a few days after the fever onset and spread to involve the rest of the body. As this disease is caused by bacteria, it is treated with antibiotics. If you experience fever, headache, nausea, vomiting, muscle pain or a rash after possible tick exposure, seek help!

While considered a tick-borne disease, Tularemia caused by the bacteria Francisella tularensis, can also be transmitted directly by contact with infected blood of animals such as rabbits and prairie dogs during activities such as hunting. The ticks known to transmit this disease are the Rocky Mountain wood tick and American dog tick. Historically, Tularemia prevalence in Colorado was low, however there were 52 documented cases in 2015, occurring mostly in Boulder and Larimer counties.  Symptoms most commonly include swollen lymph nodes (lymphadenopathy) and if spread to the respiratory tract, infections such as pneumonia. This disease may also present with localized symptoms of skin ulcers at the location of contact of tick bite or animal blood.  Antibiotics will cure this disease.

Tick-borne Relapsing Fever, caused by the bacteria Borrielia hermsii, is quite rare in Colorado as well. It is carried by the soft tick Ornithodorus hermsi and associated with nesting rodents. This disease is usually spread when a person is bitten by this tick while sleeping in cabins where rodents are present. Symptoms occur in a 3-day cyclical pattern and include high fever, headache, and muscle and joint aches. Since it is bacterial, this tick-borne disease is treated with antibiotics as well.

Not caused by a virus or bacteria, Tick paralysis is a reaction to tick saliva caused by neurotoxins produced in the salivary glands of the female Rocky Mountain wood tick. This can occur if the tick remains attached for a long period of time. Symptoms include difficulty walking within hours to a day of tick exposure and can progress to limb numbness and difficulty breathing. While this sounds frightening, there is good news: these symptoms are COMPLETELY reversible once the tick is removed, with symptoms resolving in days to a week.

A tick talk is never complete without discussing Lyme Disease, the most prevalent tick-borne disease of humans in the US. While there have been some cases reported in Colorado, it is thought the disease originated from a black-legged tick exposure outside the state in areas from Massachusetts to Virginia, Utah, and southern Washington to northern California.  This spirochete-type bacterium (borrelia burgdorferi) is carried by black-legged ticks (deer ticks). You may not see an attached tick with this disease, as it is not the adult, rather the nymph and larval stage ticks that transmit this bacterium. The nymph and larvae look more like tiny black or pale brown dots and are extremely difficult to see during tick checks. Symptoms include the infamous non-itchy red bull’s eye rash that develops within the first month of the bite. Again, you can see generalized flu-like symptoms such as headache, fever, chills and fatigue. It is reported that early recognition and treatment can result in complete recovery, and reduces the risk of arthritic, neurologic or cardiac complications that can develop days to years later.

The infectious diseases that ticks may carry can definitely wreak havoc. This is why it is important to do what you can to prevent tick bites while enjoying the beautiful outdoors. Read Part I of this post on Tick-Borne Illness here.


  1. Cranshaw W, Peairs F, Kondrateiff B. Colorado Ticks and Tick-Borne Diseases Fact Sheet. Colorado State University Extension. https://extension.colostate.edu/topic-areas/insects/colorado-ticks-and-tick-borne-diseases-5-593/. Accessed August 5, 2020
  2. Author Unknown (2016, July). Quandry: Ticks in the High Country and what they can do to you. Summit Daily. https://www.summitdaily.com/opinion/quandary-ticks-in-the-high-country-and-what-they-can-do-to-you/ Accessed August 5, 2020
  3. DeLoughery, T. (2020, July). Tick Borne Disease. Presentation through Wilderness Medicine Society Virtual Conference. Accessed September 5, 2020.

Laurie Pinkerton is a 3rd year Physician Assistant Student studying at Drexel University in Philadelphia, PA. Originally from Northern, VA, she graduated from the University of Mary Washington in Fredericksburg, VA with a degree in Biology in 2014. She moved to Keystone to live that ski life and stayed for 2 years, working as a pharmacy tech at Prescription Alternatives and as a medical assistant at Summit Cardiology. Prior to starting PA school, she moved to Idaho where she learned about organic farming and alternative medicine.  She has loved every second of being back in Summit County and learning here at Ebert Family Practice. She looks forward to practicing Integrative Medicine in the near future.

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