Dermacentor andersoni, the Rocky Mountain wood tick, is a tick species found in North America. It vectors several human diseases. Understanding this tick and its risks is important for those in affected areas.
Physical Characteristics and Range
The Rocky Mountain wood tick has distinct features. Unfed adult females are reddish-brown to gray-brown, 5-7 mm long, nearly doubling when engorged. They have a white shield on their dorsal surface, which grays when they feed. Males are spotted gray and white, lacking this shield. All life stages are flattened; nymphs and adults have eight legs, larvae six.
These ticks are found in the Rocky Mountain region of the United States, including Nebraska, South Dakota, Arizona, New Mexico, and eastern California. They also inhabit southwestern Canada, in southern Alberta, British Columbia, and Saskatchewan. Dermacentor andersoni prefers shrublands, grasslands, and lightly wooded areas, at elevations between 4,000 and 10,500 feet, especially along trails.
Its two-to-three-year life cycle requires each stage (larva, nymph, adult) to take a blood meal. Larvae and nymphs feed on small mammals; adults seek larger hosts like deer, livestock, dogs, and humans. Adult ticks are most active in spring and early summer.
Diseases Transmitted
Dermacentor andersoni vectors several diseases. These include Rocky Mountain Spotted Fever (RMSF), Colorado Tick Fever (CTF), and tick paralysis. Not every bite transmits disease, but transmission is possible, especially with prolonged attachment.
Rocky Mountain Spotted Fever (RMSF) is a bacterial infection caused by Rickettsia rickettsii bacteria. Symptoms appear 2-14 days after a bite, including fever, headache, and a rash often beginning on wrists and ankles before spreading. If untreated, RMSF can lead to severe complications, including organ damage, gangrene, and death. Antibiotic treatment is effective, especially if initiated early.
Colorado Tick Fever (CTF) is a viral illness caused by the Colorado Tick Fever virus. Initial symptoms (1-14 days after a bite) include fever, chills, headache, muscle aches, and fatigue. Many experience a “biphasic” fever, with symptoms improving for a few days before returning. Most cases are mild and resolve, but some patients, especially children, can develop severe neurological complications like meningitis or encephalitis, though rare. No specific vaccines or antiviral medications exist for CTF; treatment focuses on symptom management.
Tick paralysis is a rare but serious condition caused by a neurotoxin in certain female tick saliva, including Dermacentor andersoni. This toxin leads to ascending paralysis, starting with leg weakness and progressing upward, potentially affecting respiration. Symptoms manifest after the tick feeds for several days (often 3-7 days). It can be fatal if the tick is not found and removed, but symptoms resolve within 24-72 hours after tick removal as the body clears the toxin.
Prevention and Safe Removal
Preventing tick bites avoids tick-borne illnesses. When outdoors in tick habitats, wear protective clothing like long-sleeved shirts and pants, tucking pant legs into socks or boots for a physical barrier. Apply insect repellents with DEET to exposed skin and clothing to deter ticks.
After outdoor activities, conduct thorough tick checks on yourself, children, and pets. Ticks often migrate to warm, moist body areas; focus on the scalp, behind the ears, armpits, groin, and behind the knees. Prompt removal of an attached tick reduces the risk of disease transmission.
If a tick is found embedded, remove it immediately using fine-tipped tweezers. Grasp the tick as close to the skin as possible (ideally at its head or mouthparts), and pull upward with steady, even pressure. Avoid twisting, jerking, or squeezing the tick’s body, as this can cause mouthparts to break off or force infectious fluids into the bite. After removal, clean the bite area with soap and water or rubbing alcohol. Dispose of the tick by sealing it in tape, placing it in a sealed container, or flushing it down a toilet.
Recognizing Symptoms
After a tick bite, monitor for symptoms, as tick-borne illnesses may not appear immediately. General signs of infection include fever, chills, headache, muscle aches, fatigue, and swollen lymph nodes. Some illnesses also present with a rash, which can vary.
Symptoms can appear days to weeks after a bite. If concerning symptoms appear after a known or suspected tick bite, seek medical attention. Inform the healthcare provider about recent tick exposure (when and where the bite occurred). This information aids diagnosis and timely management, even if a rash or fever is the only symptom.