Tick

Ticks
Adult deer tick, Ixodes scapularis
Scientific classification
Kingdom:	Animalia
Phylum:	Arthropoda
Subphylum:	Chelicerata
Class:	Arachnida
Subclass:	Acarina
Superorder:	Parasitiformes
Order:	Ixodida
Superfamily:	Ixodoidea
Families
Ixodidae - Hard ticks Argasidae - Soft ticks Nuttalliellidae
Diversity
18 genera, c. 900 species

Tick is the common name for the small arachnids in superfamily Ixodoidea that, along with other mites, constitute the Acarina. Ticks are ectoparasites (external parasites), living by hematophagy on the blood of mammals, birds, and occasionally 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, tularemia, tick-borne relapsing fever, babesiosis, ehrlichiosis and Tick-borne meningoencephalitis, as well as anaplasmosis in cattle and canine jaundice.^[2].

Habitats and behaviors

Ticks are blood-feeding parasites that are often found in tall grass where they will wait to attach to a passing host. A tick will attach itself to its host by inserting its chelicerae (cutting mandibles) and hypostome (feeding tube) into the skin. The hypostome is covered with recurved teeth and serves as a hammer.^[3]

Physical contact is not the only method of transportation for ticks. Ticks can't jump or fly. Some species stalk the host from ground level, emerging from cracks or crevices located in the woods or even inside a home or kennel, where infestations of "seed ticks" (the six-legged stage of newborn ticks) can attack in numbers up to 30,000 at a time. Weak or elderly dogs, puppies, and cats are particularly endangered and can die from anemia from a sudden influx of seed ticks. Seed ticks also attack horses, cattle, moose, lions and other mammals, causing anemia, various diseases, paralysis and even death. Such infestations can be difficult to detect until thousands have attached themselves to an animal and eradication can be difficult.^[4][5]

Mature ticks are harder to see. Frequent grooming and chemicals for control may control the spread of seed ticks and adults.^[6]

Changes in temperature and day length are some of the factors signalling a tick to seek a host. Ticks can detect heat emitted or carbon dioxide respired from a nearby host. They will generally drop off the animal when full, but this may take several days. In some cases ticks will live for some time on the blood of an animal. Ticks are more active outdoors in warm weather, but can attack a host at any time.^[7]

Ticks can be found in most wooded or forested regions throughout the world. They are especially common in areas where there are deer trails or human tracks. Ticks are especially abundant near water, where warm-blooded animals come to drink, and in meadows wherever shrubs and brush provide woody surfaces and cover.

Population control

Ticks are a vector for a number of diseases including Lyme disease, Rocky Mountain spotted fever and other Tick-borne disease.

Case study of the American Deer Tick

The blacklegged or deer tick (Ixodes scapularis) is dependent on the white-tailed deer for reproduction. Larval and nymph stages (immature ticks that cannot reproduce) of the deer tick feed on birds and small mammals. The adult female tick needs a large 3 day blood meal from the deer before she can reproduce and lay her 2000 or more eggs. Deer are the primary host for the adult deer tick and are key to the reproductive success of the tick.^[8] See the Connecticut Agricultural Experiment Station and Connecticut Department of Public Health joint publication "Tick Management Handbook" for more details of the tick's life cycle and dependence on deer.^[9]

Numerous studies have shown that abundance and distribution of deer ticks are correlated with deer densities.^{[8][10][11][12]}

When the deer population was reduced by 74% at a 248-acre (100 ha) study site in Bridgeport, Connecticut, for example, the number of nymphal ticks collected at the site decreased by 92%.^[8] The relationship between deer abundance, tick abundance, and human cases of Lyme disease was well documented in the Mumford Cove Community in Groton, Connecticut, from 1996 to 2004. The deer population in Mumford Cove was reduced from about 77 deer per square mile to about 10 deer per square mile (4 deer per square kilometer) after 2 years of controlled hunting. After the initial reduction the deer population was maintained at low levels. Reducing deer densities to 10 deer per square mile (4 deer per square kilometer) was adequate to reduce by more than 90% the risk of humans contracting Lyme disease in Mumford Cove.^[13]

A 2006 study by Penn State's Center for Infectious Disease Dynamics indicated that reducing the deer population in small areas may lead to higher tick densities, resulting in more tick-borne infections in rodents leading to a high prevalence of tick-borne encephalitis and creating a tick hot-spot.^[14]

Other control measures

Male tick size comparison to a match.

The parasitic Ichneumon wasp Ixodiphagus hookeri has long been investigated for its potential to control tick populations. It lays its eggs into ticks; the hatching wasps kill their host.

Another natural form of control for ticks is the guineafowl, a bird species which consumes mass quantities of ticks.^[15] Just 2 birds can clear 2 acres (8,100 m²) in a single year.

Topical (drops/dust) flea/tick medicines may be toxic to animals and humans. Phenothrin (85.7%) in combination with Methoprene was a popular topical flea/tick therapy for felines. Phenothrin kills adult fleas and ticks. Methoprene is an insect growth regulator that interrupts the insect's life cycle by killing the eggs. However, the U.S. Environmental Protection Agency required at least one manufacturer of these products to withdraw some products and include strong cautionary statements on others, warning of adverse reactions.^[16]

A liquid spray, duster or aerosol spray, with either a hand sprayer or a hand spreader, may be used to control tick populations.

Example species

Two families of ticks are the Ixodidae and the Argasidae.

Engorged tick attached to back of toddler's head. Adult thumb shown for scale.

Head of Ixodes ricinus (sheep tick)

Ixodes hexagonus

Ixodidae family (hardbodied)

Dermacentor

• Dermacentor variabilis, the American dog tick, is perhaps the most well-known of the North American hard ticks. This tick does not carry Lyme disease but can carry Rocky Mountain spotted fever.

Ixodes

• Ixodes scapularis (formerly Ixodes dammini), known as the black-legged tick or deer tick, is common to the eastern part of North America and is known for spreading Lyme disease.
• Ixodes pacificus, the Western black-legged tick, lives in the western part of North America and is responsible for spreading Lyme disease and Rocky Mountain spotted fever. It tends to prefer livestock such as cows as its adult host.
• Australia tick fauna consists of approximately 75 species, most of which fall into the Ixodidae, hard tick, family. The most medically important tick is the Paralysis tick, Ixodes holocyclus. It is found in a 20-kilometre band that follows the eastern coastline of Australia. Encounters with these parasites are relatively common as this is where much of the human population resides in New South Wales and South-East Queensland. Although most cases of tick bite are uneventful, some can result in life threatening illnesses including paralysis, tick typhus, and severe allergic reactions both in humans and pets.

Boophilus/Rhipicephalus

• The southern cattle tick, Boophilus microplus (Canestrini), causes annual economic losses in the hundreds of millions of dollars to cattle producers throughout the world, and ranks as the most economically important tick globally. This tick also attacks sheep, horses, goats, and a few related species, but cattle are the most important hosts.^[17]

Amblyomma

• The Lone Star tick, Amblyomma americanum, is part of the Ixodidae family. The adult females are distinguished by a white dot or "lone star" on its back. The adult males can also be seen with dots and white streaks on the edge of their bodies. This tick has been associated with transmission of Southern Tick Associated Rash Illness (STARI) in humans, which is a disease caused by a Borrelia sp. related to the agent that causes Lyme Disease.

Argasidae family (softbodied)

Members of this family include Argas and Ornithodoros.

Fossil record

Fossil ticks are common. Recent hypotheses based on total-evidence approach analysis place the origin of ticks in the Cretaceous (65–146 mya) with most of the evolution and dispersal occurring during the Tertiary (5–65 mya).^[18]. The oldest example is an argasid (bird) tick from Cretaceous New Jersey amber. The younger Baltic and Dominican ambers have also yielded examples, all of which can be placed in living genera.

See also

• Use of DNA in forensic entomology for information in using DNA to identify species.
• Tick-borne meningoencephalitis is a tick-borne viral infection.
• Paralysis tick
• Tick-borne disease
• Crimean–Congo hemorrhagic fever

References

External links

• Lyme Disease: Nature Class - March 1997.
• Stafford, Kirby C. III: Tick Bite Prevention, Connecticut Department of Public Health, Feb. 1999.
• Fivaz, B., T. Petney, and I. Horak. 1993. Tick Vector Biology: Medical and Veterinary Aspects. Springer. ISBN 0-387-54045-8.
• TickEncounter.org University of Rhode Island site with tick and tick-borne disease information *Ticks in Kansas, Kansas State University
• University of Sydney and Westmead Hospital, Dept of Entomology for more information about ticks
• Mites and Ticks chapter in United States Environmental Protection Agency and University of Florida/Institute of Food and Agricultural Sciences National Public Health Pesticide Applicator Training Manual on the UF/IFAS Featured Creatures Web site
• Dermacentor variabilis, American dog tick
• Ixodes scapularis, blacklegged or deer tick
• Rhipicephalus sanguineus, brown dog tick
•  Chisholm, Hugh, ed (1911). "ticks". Encyclopædia Britannica (Eleventh ed.). Cambridge University Press. 

Acari (ticks and mites) Acariformes Trombidiformes Sphaerolichida · Prostigmata Sarcoptiformes Endeostigmata · Oribatida Parasitiformes Opilioacarida Opilioacaridae Holothyrida Allothyridae · Holothyridae · Neothyridae Ixodida (ticks) Argasidae · Ixodidae · Nuttalliellidae Mesostigmata Sejida Sejoidea Trigynaspida Cercomegistoidea · Antennophoroidea · Celaenopsoidea · Fedrizzioidea · Megisthanoidea · Parantennuloidea · Aenictequoidea Monogynaspida Microgynioidea · Heatherelloidea · Thinozerconoidea · Polyaspidoidea · Uropodoidea · Trachyuropodoidea · Diarthrophalloidea · Epicrioidea · Zerconoidea · Arctacaroidea · Parasitoidea · Veigaioidea · Rhodacaroidea · Eviphidoidea · Ascoidea · Phytoseioidea · Dermanyssoidea