Ticks in Colorado

Nearly 30 species of tick are known to occur within Colorado. Many of these ticks pose potential risk to human, pet, livestock and/or wildlife health. Many tick species have been found outside of their previously known distribution ranges and Coloradans may encounter additional tick species within our state or when traveling.  Small mammals are important host reservoirs for many of the diseases these tick vectors may transmit. Large mammals, like deer and elk provide both blood meals and transport of ticks as they migrate between habitats, sometimes into our own back yards. Birds are very efficient transporters of ticks as well as competent host reservoirs for many tick-borne diseases. Surveillance and study of ticks within Colorado is limited, and more research is needed.

In addition to the Rocky Mountain Wood tick, American Dog tickBrown Dog tick, Lone Star tick and the Relapsing Fever ticks, the following ticks have been reported to occur here:

Dermacentor albipictus  (the winter tick)

Dermacentor albipictus female (left) and male (right) adults, collected from cervids in Wisconsin. Image courtesy of Dr. Paskewitz, UW-Madison, Department of Entomology

Dermacentor albipictus is one of the most common North American Dermacentor species. This is a one-host tick, meaning that it attaches to a host individual as a larva, molts to the next stage while still attached, and normally does not drop from that host individual until after it becomes an engorged female; males do not engorge but do feed. This tick has large geographic distribution in North America. They can be found coast to coast through much of Canada and the United States ranging from the Yukon Territory in the north to along the Mexican border in the south. It is responsible for tick worry and alopecia in moose. It can infest animals in large numbers that are sufficient to cause death from exsanguination. The primary hosts for this species are larger domestic and wild ungulates, such as horses, cattle, elk, moose, and deer, mountain goats and sheep. Because winter ticks are a one host species of large mammals, they are not considered a threat to human health, they can however, pose a significant threat to wildlife, moose in particular. It is a rare human biter.


Dermacentor parumapertus

This western hard tick species may be found in parts of Texas (west of the 100th meridian), and throughout the states of Colorado, New Mexico, Utah, Arizona, Nevada, and California. It is also found in southwestern Idaho and southeastern Oregon. Hosts are primarily rabbits, especially for immature stages, but adults have also been found on deer and coyote. Hunters and field biologists are most likely to encounter this species through contact with with wildlife, especially rabbits. Because of its nearly exclusive association with rabbits and hares, it is a likely vector of the agent of Tularemia, should it bite humans, which is unlikely.


Examples of nymph (top), female (bottom left) and male (bottom right) Haemaphysalis leporispalustris ticks. Image courtesy of Dr. Paskewitz, UW-Madison, Department of Entomology

Haemaphysalis leporispalustris (the rabbit tick)

This widespread American tick species can transmit the agents of Rocky Mountain spotted fever, Q fever, and tularemia. Hosts include rabbits for all stages; and birds, for immature stages. It is a very rare human biter.


 

Nymph of Ixodes angustus. Image courtesy of Dr. Paskewitz, UW-Madison, Department of Entomology

Ixodes angustus

This tick is widely distributed throughout North America, it ranges from Alaska and Canada to the southwestern United States,including Colorado. Its primary hosts are rodents (mice and voles), but has also been found on shrews, birds, cats and dogs. It is considered a “nidicolous” species, meaning that it does not “quest” widely in ground vegetation, but rather in cool, moist micro-habitats in or around the nests or burrows of preferred hosts. This tick is a competent sylvatic vector of Lyme disease, with suggested transmission to a child in a Washington State case study. It is known as an occasional human biter.


Ixodes baergi

Host is the cliff swallow.


 

Adult female Ixodes cookei. Photo courtesy of Dr. Paskewitz, UW-Madison, Department of Entomology

Ixodes cookei  (the groundhog or woodchuck tick)

This hard tick species is very similar in appearance to Ixodes scapularis. It is common and widespread on American wildlife, primarily east of the Rocky Mountains. The natural transmission cycle of Powassan virus includes the enzootic or sylvatic transmission between Ixodes cookei and small and medium-sized rodents (mice and voles) and carnivores. The primary hosts for this tick are a variety of carnivores (including domestic cats and dogs) and rodents and can be especially abundant on groundhogs (Marmota monax). It is considered a nidicolous species, meaning that it does not typically “quest” widely in ground vegetation, but inhabits cool, moist microhabitats in or around the nests or burrows of preferred hosts. It is known as an occasional human biter.


Ixodes howelli

Hosts include primarily cliff swallows, but also the gray-crowned rosy finch, the prairie falcon, and the gyrfalcon.


Ixodes kingi  (the rotund tick)

This hard tick occurs throughout western North America and occasionally in the east. It is commonly found in prairie habitats, but may also occur in shrubland and forested habitats. It has been recorded from domestic animals, including cats and dogs, several species of carnivores and rodents, and a few lagomorphs. Hosts include pocket gophers, kangaroo rats, and sigmodontine mice in areas west of the Rocky Mountains; and carnivores, ground squirrels, and prairie dogs in areas east of the Rockies. Observations from Colorado show I. kingi commonly infesting rodents (such as grasshopper mice). This species has been found to be infected with the agents of Q-fever and tularemia. It is known to bite humans rarely.


Ixodes marmotae

Hosts of this species include marmots, porcupines, wood rats, and ground squirrels.


 

Nymph of Ixodes marxi. Image courtesy of Dr. Paskewitz, UW-Madison, Department of Entomology

Ixodes marxi

This hard tick is most commonly associated with squirrels, but chipmunks, fox and raccoons are also hosts. The natural transmission cycle of Powassan virus includes the enzootic or sylvatic transmission between Ixodes marxi and small and medium-sized rodents (mice and voles) and carnivores.


Ixodes ochotonae

Hosts include pikas, woodrats, chipmunks, pocket gophers, voles, and native mice.


 

Adult female Ixodes sculptus. Photo courtesy of Dr. Paskewitz, UW-Madison, Department of Entomology

Ixodes sculptus

This tick occurs throughout western North America; occasionally in the east. It is commonly found in prairie habitats, but may also occur in shrubland and forested habitats. It is most commonly associated with squirrels, usually burrowing mammals, and their predators. It can harbor Colorado tick fever virus, though vector competence for transmission to humans has yet to be assessed. A study in Colorado found that hosts include several species of burrowing mammals, especially thirteen-lined ground squirrels (Spermophilus tridecemlineatus). Several species of carnivores, including domestic dogs, cats, as well as rodents, lagomorphs (rabbits) and goats have also been found to host this tick. It is a rare human biter.


Ixodes spinipalpis

Ixodes spinipalpis, Image is courtesy of Joel Hutcheson, USDA APHIS National Veterinary Laboratory

This hard tick is a wide ranging species throughout the western US. It is a sylvatic vector of the agents of  Lyme disease, human granulocytic ehrlichiosis/anaplasmosis, and human babesiosis. Adults and immature feed on numerous species of rodent hosts that have been found to harbor these pathogens in Colorado; the Mexican pack rat, prairie vole and deer mouse have been documented in a Colorado study. Lagomorphs (rabbits) are also hosts. A recent study in Canada documented this tick on an eastern cottontail. This species is considered “nidicolous”, meaning that it remains within the host species nest; however, studies in California and Colorado have documented questing behavior with these ticks in areas of wooded habitat.  This tick has been recorded during bird banding studies in Colorado and Canada. Studies suggest that these ticks avoid arid open grassy habitats, but questing behavior in wooded habitats may increase human exposure potential to diseases, including Lyme, Anaplasmosis and Babesia in Colorado and in other regions of the US and Canada where this tick occurs. More surveillance and research is needed regarding this tick’s potential risk to human health. It is known as an occasional human biter.


Adult female Ixodes texanus, Image courtesy of Dr. Paskewitz, UW-Madison, Department of Entomology

Ixodes texanus

Hosts include weasels, badgers, skunks, and other mustelid carnivores in the western US, and primarily raccoons in the eastern US. Occasional hosts include opossums, rodents, and lagomorphs. It is a rare human biter.


Ixodes woodi

Hosts include primarily woodrats, but also other rodents, birds, shrews. It is an incidental human biter.


Soft Ticks

Argas cooleyi

Hosts include birds, especially cliff swallows.


Carios kelleyi


Carios kelleyi (Bat Tick), Image by James Gathany-CDC

This soft tick is widely distributed in the US, collected from at least 24 states (California to New York, and from New Mexico and Texas to Minnesota). Hosts for this tick species are bats. Unlike many species of argasid ticks, C. kelleyi larvae are slow feeders requiring days (9-20) to engorge, which may explain the widespread distribution of this species as it may be easily transported by its host. A Borrelia bacterium has been identified in this tick a as a relapsing fever spirochete most closely related to, but distinct from Borrelia turicatae. The name Borrelia johnsonii is proposed for this novel spirochete in honor of Dr. Russell C. Johnson. Human encounters may occur when bats vacate roosts or hibernacula, especially if roosting in homes. It is a known human biter.


Otobius megnini  (the spinose ear tick)

This one-host tick attaches most often deep within the host ear canal as larvae and drop from that host as engorged nymphs; adults do not feed.  Hosts include wild and domestic ungulates, especially pronghorns, and occasionally humans. Spinose ear ticks are generally associated with semiarid or arid environments such as those found in the southwestern US, however they can also be found in other climate areas due to transportation of livestock. Larvae and nymphs usually remain within the ears of their host. Fully grown nymphs and adults live off of the host, but still within the host’s general environment. They usually prefer dry, protected places such as in cracks and crevices or under logs and fence posts.


Otobius nymph-Image by CDC

Otobius lagophilus

This tick is rarely encountered in Colorado. Otobius spp. are one-host ticks that attach as larvae and feed for weeks before dropping from the host as engorged nymphs. The adults do not feed. Unlike O. megnini, it usually attaches elsewhere on the head of its host, rather than in the ear canal like the Spinose Ear tick. Hosts of this species are lagomorphs (rabbit, hare, and pika).