Ixodida  

Ticks are small arachnids in the order Ixodida. Along with mites, they constitute the subclass Acarina. Ticks are ectoparasites (externalparasites), living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians. Ticks are vectors of a number of diseases, including Lyme disease, Q fever (rare; more commonly transmitted by infected excreta),^[1] Colorado tick fever, Rocky Mountain spotted fever, African tick bite fever, tularemia, tick-borne relapsing fever, babesiosis, ehrlichiosis, Tick paralysis and tick-borne meningoencephalitis, as well as bovine anaplasmosis.

Of the three families of 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]

The Argasidae contain 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 are Antricola, Argas, Nothaspis, Ornithodoros, and Otobius.^[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 family Nuttalliellidae contains only a single species, Nuttalliella namaqua, a tick found in southern Africa from Tanzania to Namibia and South Africa,.^[2][6] It can be distinguished from ixodid ticks and argasid ticks by a combination of characters, including the position of the stigmata, lack of setae, strongly corrugated integument, and form of the fenestrated plates.^[7]

Fossilized ticks are common. Recent hypotheses based on total-evidence approach analysis place the origin of ticks in the Cretaceous (65 to 146 million years ago), with most of the evolution and dispersal occurring during the Tertiary (5 to 65 million years ago).^[8] The oldest example is an argasid (bird) tick from Cretaceous New Jersey amber. The younger Baltic andDominican ambers have also yielded examples, all of which can be placed in living genera.

Tick-borne disease [edit]

Tick-borne illnesses are caused by infection with a variety of pathogens, including Rickettsia and other types of bacteria, viruses, and protozoa. 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 include Lyme disease, Rocky Mountain spotted fever, relapsing fever,tularemia, tick-borne meningoencephalitis, Colorado tick fever, Crimean-Congo hemorrhagic fever, babesiosis, and cytauxzoonosis. A recent find is Candidatus neoehrlichia mikurensis, a bacterium which causes blood clots; present in 9% of rodents, it mainly affects persons with lowered immune defense, and can be cured with antibiotics.^[18]

Tick bites may also induce a delayed allergy to red meat, involving the oligosaccharide, galactose alpha-1,3-galactose: the food-induced reactions, including anaphylaxis, 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 the ovaries, 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-tipped tweezers can 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, a punch biopsy may be necessary to remove any parts left inside the patient.^[24]