Dermacentor andersoni, commonly known as the Rocky Mountain wood tick, is a hard tick with 3 life stages including: larvae, nymph and adult. This tick is generally located in the NW United States and SW Canada along the Rocky Mountains. This tick is generally a vector for Colorado tick fever but can also be a vector for Rocky Mountain Spotted Fever and Tularemia. During the larvae and nymph stages, the tick will not feed on humans but the adult stage will. However, the larvae and nymph forms will feed on small mammals including dogs and other wildlife. Prevention of becoming infected from the possible diseases is based on control of the vector including: wearing proper clothing when in woods/wet areas and checking oneself after returning home. The adult females can feed for up to 5–15 days, thus it is very important to remove a tick if present. Follow general tick removal tips.
Dermacentor andersoni is a three-host tick with larval, nymph and adult life stages. During each life stage, the tick will take a single blood meal from a mammalian host. The duration of the life cycle varies between 1–3 years and is influenced by factors such as temperature, humidity and host availability. During May to June, the eggs are deposited on moist vegetation after the engorged female tick drops off the host. The female lays approximately 2500-4000 eggs over 10–33 days. Larval ticks hatch in early summer and begin questing for small mammalian hosts, using external stimuli such as: carbon dioxide, light, temperature or humidity. Larvae cling to a passing host with the first pair of legs, climb upwards and then attach with their gnathostome to the neck or shoulder region. They feed about 2–6 days. After becoming engorged, larvae drop off the host and molt into nymphs. Nymphs remain dormant for extended periods of time unless stimulated by presence of a host. Nymph feeding behavior is like that of larvae. Nymphs and larvae do not feed on humans. Adult females feed continuously throughout their time on the host approximately 5–15 days. Males, on the other hand, feed a shorter period and copulate with several, partially fed females that are still on the host. Females will drop off the host when fully engorged and seek an area to oviposit. Both sexes die shortly after reproducing.
Dermacentor andersoni are hard ticks that are generally brown or reddish brown in color. Females have a distinct dorsal silver-gray ornamentation which turns more gray when the tick feeds, while males are spotted gray and white with no distinctive shield marking. Their bodies are flat and pear-shaped, ranging from 2 to 5.3 mm in length and have 11 festoons on their lower dorsal portion. This species is sexually dimorphic; females are generally larger and can increase their size nearly three times its original when fully engorged. This species is also polymorphic, with a lot of physical variation between individuals. Features that distinguish this species from other ticks include the number and size of goblets which are used for respiration on its spiracular plates, Dermacentor andersoni typically have 100-200 goblets on average. This is only observable with a light microscopy.
Dermacentor andersoni ticks are generally a vector for Colorado tick fever and can possibly be a vector for Rocky Mountain Spotted Fever and Tularemia. However, the related species, Dermacentor varabilis is more susceptible to be a vector for Rocky Mountain Spotted Fever than D. andersoni. As stated above, D. andersoni is generally located in the NW USA/ SW Canada whereas D. varabilis is generally located in the eastern USA. The border separating these two-different species could be considered the Missouri River. Thus, if one was to find a Dermacentor tick on themselves when they are west of the Missouri River, they would be at a higher risk for Colorado tick fever than Rocky Mountain Spotted Fever. The tick can become infected with a disease by feeding on a small mammal during its larvae or nymph stage and will generally be a vector in its nymph or adult stage.
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