Background
Ticks can carry and transmit a remarkable array of pathogens, including bacteria, spirochetes, rickettsiae, protozoa, viruses, nematodes, and toxins. A single tick bite can transmit multiple pathogens, a phenomenon that has led to atypical presentations of some classic tick-borne diseases. In the United States, ticks are the most common vectors of vector-borne diseases (see the images below).

See Lyme Disease and 4 Emerging Tick-Borne Illnesses, a Critical Images slideshow, to help identify and treat several tick-borne conditions.
Also, see the Bug Bites You Need to Know This Summer slideshow for helpful images and information on various bug bites.
In North America, the following diseases are caused by tick bites:
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Human granulocytic and monocytic ehrlichiosis
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Tick paralysis
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Powassan virus infection
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Heartland virus infection
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Borrelia miyamotoi infection
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Borrelia mayonii infection
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Anaplasmosis
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Bourbon virus infection
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Rickettsia parkeri rickettsiosis
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Southern tick-associated rash illness (STARI)
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346D rickettsiosis
In Europe, the list is similar, but other diseases should be considered as well, including boutonneuse fever (caused by a less virulent spotted fever rickettsial organism, Rickettsia conorii) and tick-borne encephalitis. [1] No postexposure treatment is available for tick-borne encephalitis, but vaccines are in use for prevention. [2, 3, 4]
Animal and human studies have shown that the risk of Lyme disease transmission increases significantly after 24 hours of attachment and is even higher after more than 48 hours of attachment. [5] Testing of ticks for tick-borne infectious organisms is generally not recommended, except for research purposes.
Healthcare practitioners, particularly those in areas where Lyme disease is endemic, should become familiar with the clinical manifestations of, and recommended testing and therapy for, Lyme disease; they should be equally knowledgeable regarding human granulocytic ehrlichiosis (HGE) and babesiosis. If necessary for identification and testing, ticks can be placed in a sealed container containing alcohol.
For patient education resources, see the Tick Management Handbook developed by the Connecticut Agricultural Experiment Station, available from the Centers for Disease Control and Prevention (CDC).
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Ixodes scapularis mimicking a nevus at first glance. Image courtesy of Justin Finch, MD.
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Ixodes scapularis close-up. Image courtesy of Justin Finch, MD.
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Ixodes scapularis, tick vector for babesiosis. Courtesy of the Centers for Disease Control and Prevention.
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Typical appearance of erythema migrans, the bull's-eye rash of Lyme disease.
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Alopecia areata affecting the arms.
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Grasp the tick as close to the skin surface as possible and pull upward with steady, even traction.
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Bulls-eye rash