tick

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tick,

small, parasitic arachnid of the order Ixodida, closely related to the mitesmite,
small, often microscopic arachnid that belongs to several orders in the subclass Acari (or Acarina), to which the tick also belongs; mites and ticks are related to the spiders.
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. Ticks, which are larger than the often microscopic mites, are all parasitic in at least one developmental stage; most parasitize mammals and birds although some have reptilian and amphibian hosts. The unsegmented body is typically oval and compact, and there are four pairs of legs. The movable head is attached to the body by a hinge. There are four stages in the tick life cycle: egg, larva, nymph, and adult, but soft ticks may go through several nymphal states. An anchoring structure in the tick's mouth enables it to embed its entire head under the skin of the host, where it sucks the host's blood. If a tick is pulled off the host, the head usually remains embedded in the skin. Members of the family (Argasidae) of soft ticks, with a membranous outer covering, hide in crevices and come out at night to suck blood; their bites are typically painful. Hard ticks (family Ixodidae), which have thickened outer plates made of chitinchitin
, main constituent of the shells of arthropods. Chitin, a polysaccharide (see carbohydrate) analogous in chemical structure to cellulose, consists of units of a glucose derivative (N-acetyl-d
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, remain attached to the host for long periods; their bites are typically painless.

Ticks transmit Rocky Mountain spotted feverRocky Mountain spotted fever,
infectious disease caused by a rickettsia. The germ is harbored by wild rodents and other animals and is carried by infected ticks that attach themselves to humans.
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, tularemiatularemia
or rabbit fever,
acute, infectious disease caused by Francisella tularensis (Pasteurella tularensis). The greatest incidence is among people who handle infected wild rabbits.
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, Lyme diseaseLyme disease
or Lyme borreliosis,
a nonfatal bacterial infection that causes symptoms ranging from fever and headache to a painful swelling of the joints. The first American case of Lyme's characteristic rash was documented in 1970 and the disease was first identified
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, equine encephalitisequine encephalitis
, infectious disease of horses caused by any of several viruses, four of which—the Eastern, Western, Venezuelan, and St. Louis viruses—can also infect humans.
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, several forms of ehrlichiosisehrlichiosis
, any of several diseases caused by rickettsia of the genus Ehrlichia. Ehrlichiosis is transmitted by ticks. Both human forms tend to develop about nine days after a tick bite.
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, and other diseases. Tick-borne diseases of livestock (e.g., babesiosisbabesiosis
, tick-borne disease caused by a protozoan of the genus Babesia. Babesiosis most commonly affects domestic and wild animals and can be a serious problem in cattle, but since the mid-20th cent. the disease has also been found in humans.
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, anaplasmosisanaplasmosis
, infectious blood disease in cattle, sheep, and goats, caused by a rickettsia of the genus Anaplasma. The organism parasitizes red blood cells, causing their destruction and producing emaciation, anemia, jaundice, and, occasionally, death.
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) are of great economic significance. Each species needs three different hosts to complete its life cycle. Typically the larval stage will feed on small reptiles, birds, or mammals; the nymph stage will parasitize larger vertebrates; and adults will parasitize large herbivores and livestock. The adult of the ixodid species Ixodes scapularis, the vector of Lyme disease and babesiosis in the E United States and Canada, usually chooses deer as its host (I. scapularis of all stages will feed on humans). The closely related I. pacificus, which transmits Lyme disease and Rocky Mountain spotted fever in the western states, prefers livestock in the adult stage. Ticks can sometimes harbor more than one disease organism at a time.

Ticks belong in the phylum ArthropodaArthropoda
[Gr.,=jointed feet], largest and most diverse animal phylum. The arthropods include crustaceans, insects, centipedes, millipedes, spiders, scorpions, and the extinct trilobites.
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, subphylum ChelicerataChelicerata
, subphylum of Arthropoda, including the horseshoe crabs (order Xiphosura), the arachnids (class Arachnida), and the sea spiders (class Pycnogonida). The extinct giant water scorpions (order Eurypterida, not true scorpions) also are chelicerates.
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, class Arachnida, superorder Parasitiformes, order Ixodida.

tick

[tik]
(communications)
A pulse broadcast at 1-second intervals by standard frequency and time broadcasting stations to indicate the exact time.
(computer science)
A time interval equal to ¹⁄₆₀ second, used primarily in discussing computer operations.
(invertebrate zoology)
Any arachnid comprising Ixodoidea; a bloodsucking parasite and important vector of various infectious diseases of humans and lower animals.

tick

1
Commerce the smallest increment of a price fluctuation in a commodity exchange. Tick size is usually 0.01% of the nominal value of the trading unit

tick

2
1. any of various small parasitic arachnids of the families Ixodidae (hard ticks) and Argasidae, (soft ticks), typically living on the skin of warm-blooded animals and feeding on the blood and tissues of their hosts: order Acarina (mites and ticks)
2. any of certain other arachnids of the order Acarina
3. any of certain insects of the dipterous family Hippoboscidae that are ectoparasitic on horses, cattle, sheep, etc., esp the sheep ked

tick

1
1. the strong covering of a pillow, mattress, etc.
2. Informal short for ticking

tick

2
Brit informal account or credit (esp in the phrase on tick)

tick

1. A jiffy (sense 1). 2. In simulations, the discrete unit of time that passes between iterations of the simulation mechanism. In AI applications, this amount of time is often left unspecified, since the only constraint of interest is the ordering of events. This sort of AI simulation is often pejoratively referred to as "tick-tick-tick" simulation, especially when the issue of simultaneity of events with long, independent chains of causes is handwaved. 3. In the FORTH language, a single quote character.

tick

One clock cycle, or one "tick" of the clock. See clock cycle.