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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.
..... Click the link for more information. . 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
..... Click the link for more information. , 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 bacterium is harbored by wild rodents and other animals and is carried by infected ticks of several species that attach themselves to humans.
..... Click the link for more information. , tularemiatularemia
or rabbit fever,
acute, infectious disease caused by Francisella tularensis (Pasteurella tularensis). The greatest incidence is among people who handle infected wild rabbits.
..... Click the link for more information. , 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
..... Click the link for more information. , equine encephalitisequine encephalitis
, infectious disease of horses caused by any of several viruses, three of which—the Eastern, Western, and Venezuelan viruses—can also infect humans.
..... Click the link for more information. , several forms of ehrlichiosisehrlichiosis
, any of several diseases caused by rickettsia of the genera Ehrlichia and Anaplasma. Ehrlichiosis is transmitted by ticks. Both human forms tend to develop about nine days after a tick bite.
..... Click the link for more information. , 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.
..... Click the link for more information. , 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.
..... Click the link for more information. ) 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. Rapidly multiplying Asian long-horned ticks, Haemaphysalis longicornis, can also kill a young animal when the growing offspring consume a large quantity of its blood.
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.
..... Click the link for more information. , 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.
..... Click the link for more information. , class Arachnida, superorder Parasitiformes, order Ixodida (or Metastigmata).