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Ticksare smallarachnidsin theorderIxodida. Along withmites, they constitute the subclassAcarina. Ticks areectoparasites(externalparasites), living byhematophagyon the blood of mammals, birds, and sometimes reptiles and amphibians. Ticks arevectorsof a number of diseases, includingLyme disease,Q fever(rare; more commonly transmitted by infected excreta),^[1]Colorado tick fever,Rocky Mountain spotted fever,African tick bite fever,tularemia, tick-bornerelapsing fever,babesiosis,ehrlichiosis,Tick paralysisandtick-borne meningoencephalitis, as well as bovineanaplasmosis.

Of the threefamiliesof ticks, one –Nuttalliellidae– comprises a single species,Nuttalliella namaqua. The remaining two families contain the hard ticks (Ixodidae) and the soft ticks (Argasidae).^[2][3]

Ixodidae(>700 species) are distinguished from the Argasidae by the presence of a scutum or hard shield. In Ixodidae nymphs and adults, a prominent capitulum (head) projects forwards from the body; in the Argasidae, conversely, the capitulum is concealed beneath the body.^[4]

TheArgasidaecontain 193 species, although the composition of the genera is less certain, and more study is needed before the genera can become stable.^[2]The currently accepted genera areAntricola,Argas,Nothaspis,Ornithodoros, andOtobius.^[2]Though common in North America, they feed rapidly, primarily on birds, and are very rarely found to parasitize land animals or humans.^[5]

The familyNuttalliellidaecontains only a single species,Nuttalliella namaqua, a tick found in southernAfricafromTanzaniatoNamibiaandSouth Africa,.^[2][6]It can be distinguished fromixodid ticksandargasid ticksby a combination of characters, including the position of the stigmata, lack of setae, strongly corrugated integument, and form of the fenestrated plates.^[7]

Fossilized ticksare common. Recent hypotheses based on total-evidence approach analysis place the origin of ticks in theCretaceous(65to146million years ago), with most of the evolution and dispersal occurring during theTertiary(5to65million years ago).^[8]The oldest example is an argasid (bird) tick from CretaceousNew Jerseyamber. The youngerBalticandDominican ambershave also yielded examples, all of which can be placed in living genera.

Tick-borne disease[edit] Main article:Tick-borne disease

Tick-borne illnesses are caused by infection with a variety ofpathogens, includingRickettsiaand other types ofbacteria,viruses, andprotozoa. Because ticks can harbor more than one disease-causing agent, patients can be infected with more than one pathogen at the same time, compounding the difficulty in diagnosis and treatment. Major tick-borne diseases includeLyme disease,Rocky Mountain spotted fever,relapsing fever,tularemia,tick-borne meningoencephalitis,Colorado tick fever,Crimean-Congo hemorrhagic fever,babesiosis, andcytauxzoonosis. A recent find isCandidatus neoehrlichia mikurensis, a bacterium which causes blood clots; present in 9% ofrodents, it mainly affects persons with lowered immune defense, and can be cured with antibiotics.^[18]

Tick bites may also induce a delayed allergy tored meat, involving theoligosaccharide, galactose alpha-1,3-galactose: the food-inducedreactions, includinganaphylaxis, characteristically present several hours after eating in subjects who have experienced a large local reaction to tick bites up to six months earlier.^[19][20]

Eggs can be infected with pathogens inside theovaries, meaning the larval ticks can be infectious immediately at hatching, before feeding on their first host.^[17]

In general, the best way to remove an adult tick is mechanically. To facilitate prompt removal, fine-tippedtweezerscan be used to grasp the tick as close to the skin as possible and detach it by applying a steady upward force without crushing, jerking or twisting, in such a way as to avoid leaving behind mouthparts or provoking regurgitation of infective fluids into the wound.^[21][22][23]Proprietary tick removal tools are also available.^[21][22]It is important to disinfect the bite area thoroughly after removal of the tick.^[23]The tick can be stored and, in case of signs or symptoms of a subsequent infection, shown to a clinician for identification purposes together with details of where and when the bite occurred.^[21]If the tick's head and mouthparts are no longer attached to its body after removal, apunch biopsymay be necessary to remove any parts left inside the patient.^[24]