Colorado Ticks and Tick-Borne Diseases Fact Sheet No. 5.593 Insect Series|Trees and Shrubs by W.S. Cranshaw, F.B. Peairs and B.C. Kondratieff* Ticks are blood-feeding parasites of Quick Facts animals found throughout Colorado. They are particularly common at higher elevations. • The most common tick that Problems related to blood loss do occur bites humans and dogs among wildlife and livestock, but they are in Colorado is the Rocky rare. Presently 27 species of ticks are known Mountain wood tick. to occur in Colorado and Table 1 lists the more common ones. Almost all human • Rocky Mountain wood tick is encounters with ticks in Colorado involve most active and does most the Rocky Mountain wood tick. Fortunately, biting in spring, becoming some of the most important tick species dormant with warm weather in present elsewhere in the United States are summer. Figure 1: Adult Rocky Mountain wood tick prior either rare (lone star tick) or completely to feeding. Rocky Mountain wood tick is the most • Colorado tick fever is by far absent from the state (blacklegged tick). common tick that is found on humans and pets in Ticks most affect humans by their ability Colorado. the most common tick- to transmit pathogens that produce several transmitted disease of the important diseases. Diseases spread by ticks region. Despite its name, in Colorado include Colorado tick fever, Rocky Mountain spotted fever Rocky Mountain spotted fever, tularemia and is quite rare here. relapsing fever. • Several repellents are recommended for ticks Life Cycle of Ticks including DEET, picaridin, Two families of ticks occur in Colorado, Figure 2: Adult female and male of the Rocky IR3535, and oil of lemon hard ticks (Ixodidae family) and soft ticks Mountain wood tick. Photograph courtesy of the eucalyptus. CDC Photo Image Library. (Argasidae family). Hard ticks can be distinguished by the presence of a plate • To remove a tick, grasp it with (scutellum) on the back behind the head. The larva, nymph and adult ticks are tweezers, as close to the skin They also have mouthparts that are directed active and feed on blood. When fully as possible and pull it straight forward and are easily visible. The soft ticks engorged with blood their body becomes out. lack the plate, have a less regularly rounded greatly distended to the shape of a pea. body and have mouthparts that are directed With some species, the entire life cycle of a beneath the tick, so they are not visible from tick may be completed within a single year. above. The more commonly encountered ticks in Ticks go through four life stages as they Colorado usually require two or three years develop. Eggs are laid in large masses that to complete development. often total thousands of eggs. At hatch, there Hard Ticks. Most hard ticks are three is a tiny larva (“seed tick”) that is six legged. host ticks. With this life cycle pattern each After it has fed and developed it will molt to feeding stage occurs often on a different an eight-legged nymph. When this has fed animal. For example, the larva of the and developed it will molt to the final stage Rocky Mountain wood tick (Dermacentor adult. Both male and female ticks occur, andersoni) feeds on small mammals, often © Colorado State University with males usually smaller than females. a rodent. When it has completed feeding Extension. 5/00. Revised 2/19. it drops from the animal, later molts to a extension.colostate.edu *Whitney Cranshaw, Frank Peairs and Boris Kondratieff nymph stage and the nymph seeks a new are all professors of entomology in the Department of Bioagricultural Sciences and Pest Management at host. In the case of the Rocky Mountain Colorado State University. 5/00. Revised 2/19. wood tick, the nymph also feeds on small only develops only on dogs, reinfesting an animal at each stage in its development. Brown dog ticks are more abundant in warmer areas, and in Colorado are found where dogs are present continuously and are kept together in enclosed areas, such as kennels and homes. A different pattern occurs with the winter tick (Dermacentor albipictus), which is a one host tick, and the Figure 3: Life stages of a hard tick (Ixodidae). Image courtesy of the CDC Photo Image Library. only one-host tick in Colorado. All feeding stages of winter tick remain on their host – large mammals such as elk, moose, or horses. The engorged adults drop from the animal sometime in spring and lay their eggs, which hatch in late summer and early autumn. Figure 6: An adult female of the American dog tick before and after a blood meal. Photograph Soft Ticks. Soft ticks are more courtesy of David Shetlar, The Ohio State continuously associated with their host University. animal and feed more frequently than do hard ticks. Most, are usually live next to areas where their mammal host Figure 4: First stage larvae of the winter tick. (often rodents) will nest or rest for long Tick larvae are extremely small and have only 3 periods. Periodically the tick will move pairs of legs. Photograph courtesy of the Ken to feed on the host, usually at night, then Gray Collection, Oregon State University. return. Feeding times are brief and each mammals, including dogs, then drops to stage (larva, nymph adult) will feed several the ground later transforming to the adult. times as they develop. This is the habit Adults of the Rocky Mountain tick feed of Ornithodoros hermsi, the tick that is on larger mammals such deer, including associated with tick-borne relapsing fever humans. During each stage the tick may in Colorado. Figure 8: Top and bottom view of a male brown The “ear ticks” (Otobius species) have dog tick. Photograph courtesy of Jim Kalisch, feed for days, sometimes weeks, before The University of Nebraska. it becomes completely engorged blood. a somewhat different habit. They develop TheAmerican dog tick (Dermacentor as a one host tick and remain on the host variabilis), which is a common tick in animal continuously, dropping off only Tick-borne Diseases that the eastern plains areas of the state, has a when the adult is ready to lay eggs. Two Occur in Colorado species of these ticks occur in Colorado, similar life history. By far, the most common disease that When seeking a host, hard ticks will one that develops on rabbits and jackrabbits (O. lagophilus) the other (O. megnini) on is spread by ticks in Colorado is Colorado climb onto vegetation. There the tick will tick fever. This is caused by a virus and in remain immobile until a passing mammal various hooved mammals, particularly pronghorn. most people produces symptoms similar signals its presence through vibrations, to flu: headaches, fever/chills, and a feeling the warmth of the animal, and the carbon of fatigue. In about half the cases there dioxide it exhales. The tick will then will be a few days of symptoms, followed actively extend its front legs (questing) to by recovery and then a second round of latch onto the animal as it brushes against symptoms (biphasic fever). Normally it. recovery is complete, and symptoms Hard ticks can be very resistant to disappear within a few days or weeks. In starvation and nymphs and adults may rare cases, serious complications can occur survive a year without feeding. Survival when the virus infects the central nervous is shorter under warm, dry conditions system. The Rocky Mountain wood tick and many ticks will go dormant with high is the vector of Colorado tick fever and temperatures in late spring and summer. symptoms usually develop between three Most cases of ticks biting humans in Figure 5: Adult male of the Rocky Mountain and seven days after the tick bite. wood tick questing on a plant stem. This is a Colorado occur in spring and end in Rocky Mountain spotted fever summer. position the ticks take when a potential host is detected. Photograph courtesy of the Ken Gray (Rickettsia rickettsii) is caused by a Some hard ticks have slightly Collection, Oregon State University. type of bacterium. It can be a serious different life cycles. The brown dog tick disease, potentially life threatening. Early (Rhipicephalus sanguineous) is also three- symptoms include headaches and upset host tick, dropping from the host after stomach, and a rash often develops a each blood meal. However, brown dog tick few days after fever symptoms. Rocky rodents are present behind walls, from which the ticks may emerge at night to feed. also affect cattle, dogs and some other Cases of this disease in Colorado are rare, mammals. usually less than a couple per year, but can Fortunately, the most important tick- occur year-round. borne disease in North America, Lyme Tularemia (Francisella tularensis) is also disease, is not present in wild animal a bacterial disease. It can be widespread populations in Colorado (i.e., not endemic). among many wild mammals, notably There has never been a confirmed case of rabbits, prairie dogs, and muskrats. Cats Lyme disease originating from a tick-bite can also become infected. Human cases in Colorado. There are a small number most often result from contact with the of cases of Coloradoans that have been blood of an infected animal but can also diagnosed as having Lyme disease (seven Figure 8: Winter tick collected near Salida in recorded cases between 2007-2017) but March laying a mass of eggs. occur from bites of Rocky Mountain wood tick or American dog tick. In most years all of these are thought to have originated there are very few human cases of tularemia from exposure to infected ticks in states in Colorado, but in 2014-2016 there was a where this disease is present.