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Clinical Summary

Ticks are blood-sucking parasites of people and animals. Ticks cause illness by acting as vectors for pathogens or by secreting toxins or venoms. Ticks carry more types of infectious pathogens than any other arthropods except mosquitoes. The most important pathogens include Borrelia (responsible for Lyme disease and relapsing fever), Rickettsia, including Rocky Mountain spotted fever (RMSF), Ehrlichia (ehrlichiosis), viral pathogens, such as Colorado tick fever, and babesiosis. Rashes are prominent in Lyme disease, RMSF, and southern tick-associated rash illness (STARI), sometimes present in relapsing fever, uncommon in Colorado tick fever, and absent in babesiosis.

Clinically important ticks in North America include Ixodes dammini, the deer tick (Lyme disease and babesiosis); Dermacentor andersoni, the wood tick (RMSF and Colorado tick fever); Dermacentor variabilis, the dog tick (RMSF, ehrlichiosis); and Amblyomma americanum, the lone star tick (a very widespread tick implicated in the transmission of Lyme disease outside of the range of I dammini as well as STARI and ehrlichiosis). More than 40 species of ticks can cause tick paralysis. In North America, the most common cause is D andersoni, but A americanum and Ixodes species have also been associated with tick paralysis.

Tick paralysis develops 5 to 6 days after an adult female tick attaches. Over the next 24 to 48 hours, an ascending, symmetric, flaccid paralysis develops. Alternative presentations include ataxia and associated cerebellar findings without muscle weakness or isolated facial paralysis. Resolution of the paralysis after removal of the tick establishes the diagnosis.

FIGURE 16.75

Deer Tick. Ixodes dammini, the deer tick, is a vector of Lyme disease and babesiosis. (Photo contributor: Centers for Disease Control and Prevention, Atlanta, GA.)

FIGURE 16.76

Wood Tick. Dermacentor andersoni, the wood tick, is a vector of Rocky Mountain spotted fever and Colorado tick fever. (Photo contributor: Centers for Disease Control and Prevention, Atlanta, GA.)

FIGURE 16.77

Lone Star Tick. Amblyomma americanum, the lone star tick, has been implicated as a vector in STARI. (Photo contributor: Sherman Minton, MD.)

FIGURE 16.78

Imbedded Tick. This lone star tick was found imbedded in the patient’s shoulder. It was easily removed intact with tweezers. (Photo contributor: R. Jason Thurman, MD.)

FIGURE 16.79

American Dog Tick. Dermacentor variabilis, the dog tick, is a vector of Rocky Mountain spotted fever and ehrlichiosis. (Photo contributor: R. Jason Thurman, MD.)

Management and Disposition

If still embedded, the tick should be removed promptly by ...

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