Tick

From Wikipedia, the free encyclopedia

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

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 important vectors of a number of diseases, including Lyme disease. According to Pliny the Elder, ticks are "the foulest and nastiest creatures that be."^[1]

Contents 1 Habitats and behaviors 2 Population control 3 Removal 4 Example species 5 Fossil record 6 References

[edit] Habitats and behaviors

Ticks are blood-feeding parasites that are often found in tall grass and shrubs where they will wait to attach to a passing host. Physical contact is the only method of transportation for ticks. Ticks do not jump or fly, although they may drop from their perch and fall onto a host. Some species actively stalk the host by foot.

Changes in temperature and day length are some of the factors signaling 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 have a harpoon-like structure in their mouth area, known as a hypostome, that allows them to anchor themselves firmly in place while feeding. The hypostome has a series of barbs angled back, which is why they are so difficult to remove once they have penetrated a host. Ticks can be found in Scotland and forested areas of North America; they are especially common in areas where there are deer trails or horse paths.

Some of the more common diseases that can be contracted from a tick bite include (listed alphabetically): Babesiosis, Ehrlichiosis, Lyme disease, Rocky Mountain spotted fever, Southern tick-associated rash illness, Tick-borne relapsing fever, and Tularemia.

[edit] Population control

The blacklegged or deer tick (Ixodes scapularis) is dependent on the white-tailed deer for successful 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.^[2] By reducing the deer population back to healthy levels of 8 to 10 per square mile (from the current levels of 60 or more deer per square mile in the worst affected areas of the country) the tick numbers can be brought down to very low levels, perhaps too few to spread tick-borne diseases.^{[citation needed]} See the Connecticut Agricultural Experiment Station and Connecticut Department of Public Health joint publication "Tick Management Handbook" ^[3] for more details of the tick's life cycle and dependence on deer.

Numerous studies have shown that abundance and distribution of deer ticks are correlated with deer densities.^[2][4][5][6] For example when the deer population was reduced by 74% at a 248-acre study site in Bridgeport, Connecticut, the number of nymphal ticks collected at the site decreased by 92%.^[2] Furthermore, 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 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 was adequate to reduce by more than 90% the risk of humans contracting Lyme disease in Mumford Cove.^[7] Deer population management must serve as the main tool in any long-term strategy to reduce human incidences of Lyme disease.^[8]

A method of reducing deer tick (Ixodes scapularis/dammini) populations - Damminix [6] - may be cited. It consists of biodegradable cardboard tubes stuffed with permethrin-treated cotton and works in the following way: Mice collect the cotton for lining their nests. The pesticide on the cotton kills any immature ticks that are feeding on the mice. It is important to put the tubes where mice will find them, such as in dense, dark brush or at the base of a log; mice are unlikely to gather the cotton from an open lawn. Best results are obtained with regular applications early in the spring and again in late summer. The more neighbors who also use Damminix, the better. Damminix appears to help control tick populations, particularly in the year following initial use. Note that it is not effective on the West Coast. See UMM Patient Education Link.

A potential alternative to Damminix's permethrin is fipronil. It is used in the Maxforce Tick Management system, in which fipronil is painted onto rodents visiting the plastic baitboxes. see[7]. This system is no longer generally available for sale by Bayer. In 2005, there were selective reports of grey squirrels "chewing" into some Maxforce TMS boxes in areas of the northeastern United States, compromising the child resistant box. Due to this problem, the Environmental Protection Agency (EPA) asked that all similarly designed TMS boxes applied in 2006 be covered with a protective shroud capable of preventing squirrel damage. The Maxforce TMS system remains registered by the federal EPA for its continued use. A metal shroud has been developed and is reportedly in use to eliminate any potential squirrel damage to the plastic box. This shroud reportedly satisfies the EPA's mandate to protect the boxes from such damage and is recommended by Bayer Environmental Science. Availability however outside of Connecticut, New York, New Jersey and Rhode Island may be minimal.

Also, the Centers for Disease Control and Prevention offers advice on reducing ticks around your home. [8]

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 its host.

Another "natural" form of control for ticks is the Guineafowl. They consume mass quantities of ticks.^{[citation needed]} Just 2 birds can clear 2 acres in a single year.

Topical (drops/dust) flea/tick medicines need to be used with care. Phenothrin (85.7%) in combination with Methopren 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 EPA has made at least one manufacturer of these products withdraw some products and include strong cautionary statements on others, warning of adverse reactions.^[9]

[edit] Removal

To remove a tick use a small set of tweezers: grab the head, pulling slowly and steadily.^[10] There are a number of manufacturers that have produced tweezers specifically for tick removal. Crushing or irritating the tick (by heat or chemicals) should be avoided, because these methods may cause it to regurgitate its stomach contents into the skin, increasing the possibility of infection of the host.^[11] Tiny larval ticks can usually be removed using a special tick remover.^[12] Lyme disease found in deer ticks cannot be transmitted once the body is removed, even if the mouthparts break off and are still in the skin. Prompt removal is important; infection generally takes an extended period of time, over 24 hours for Lyme disease.

It is essential not to compress the abdomen of a tick during the removal, to minimize the risk of saliva back-flow; this back-flow into the skin can lead to allergic manifestations and to transmission of tick-borne microorganisms. Tweezers and similar instruments exert pressure on the digestive tract of the tick.

Tick hooks are effective tools designed to remove ticks from the skin of animals and people, without leaving the mouth-parts of the tick planted in the skin, without compressing the abdomen of the ticks, minimizing the transfer of infectious agents (e.g., Lyme disease, babesiosis).^[13]

An alternative method used by fishermen, which does not risk squeezing the tick's thorax, uses 18 inches of fine weight fishing line. The line is tied in a simple overhand knot that is tightened slowly around the tick's head. If the line is pressed against the skin while being gently pulled, the knot will tighten around the tick's head. Slowly pulling the ends of the line will then dislodge the tick from the bite site with a reduced chance of leaving the head attached. This method also works with sewing thread.

It is commonly claimed that petroleum jelly placed on the tick will clog the animal's breathing passages and cause it to detach itself. However, many medical authorities advise against this and other "smothering" approaches as ticks only breathe a few times per hour and feeding may thus continue for some time, and because these approaches may irritate the tick to the point of regurgitation of bacteria into the bloodstream.^{[14][15][10][16][17]}

Ether may also be used to anesthetize ticks to assist in removal; see diethyl ether.

[edit] Example species

• 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 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 the more deadly Rocky Mountain spotted fever. It tends to prefer livestock as its adult host.
• In some parts of Europe, tick-borne meningoencephalitis is a common viral infection.

• Australia tick fauna consists of approximately 75 species, the majority 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. As this is where much of the human population resides in New South Wales, encounters with these parasites are relatively common. Although most cases of tick bite are uneventful, some can result in life threatening illnesses including paralysis, tick typhus and severe allergic reactions. The Lone star tick is part of the Ioxdidae family, classifying it as a hard tick. 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.
• See also Use of DNA in forensic entomology for information in using DNA to identify species.^[18]

[edit] Fossil record

Fossil ticks are rare but not unknown^[19]. 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.

[edit] References

• Muma, Walter: 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