Tick

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.

Additional recommended knowledge

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Characteristics

The major families of ticks include the Ixodidae or hard ticks, which have thick outer shells made of chitin, and Argasidae or soft ticks, which have a membraneous outer surface. A third family, Nuttalliellidae, contains one rare Alaskan species, Nuttalliella namaqua. Soft ticks typically live in crevices and emerge briefly to feed, while hard ticks will attach themselves to the skin of a host for long periods of time. Ticks, like most other arachnids, typically have eight legs but may have six depending on their developmental stage. Tick bites look like mosquito bites, but can also sometimes bruise or resemble a bullseye.

Classification

This list presents all genera, but only some representatives of the almost 900 described species.

Ixodidae

• Ixodidae C. L. Koch, 1844 (13 genera, c. 700 species) — hard ticks

• Amblyomminae

• Amblyomma (c. 130 species)

• Amblyomma americanum - Lone Star Tick

• Bothriocrotoninae

• Bothriocroton Klompen, Dobson & Barker, 2002 (5 species)

• Haemaphysalinae

• Haemaphysalis C.L. Koch, 1844 (c. 170 species)

• Haemaphysalis punctata

• Hyalomminae

• Hyalomma C.L. Koch, 1844 (c. 20 species)

• Hyalomma lusitanicum
• Hyalomma marginatum

• Nosomma Schulze, 1919 (1 species)

• Ixodinae

• Cornutupalpum Poinar & Brown, 2003 (1 species)
• Ixodes C.L. Koch, 1844

• Ixodes dammini - suggested to be synonymized with Ixodes scapularis (Say) by J.H. Oliver 1993
• Ixodes holocyclus
• Ixodes persulcatus -Taiga tick
• Ixodes ricinus
• Ixodes scapularis

• Rhipicephalinae

• Anomalohimalaya Hoogstraal, Kaiser & Mitchell, 1970 (3 species)
• Cosmiomma Schulze, 1919 (1 species)
• Dermacentor C.L. Koch, 1844 (c. 30 species)

• Dermacentor albipictus
• Dermacentor andersoni - Rocky Mountain wood tick
• Dermacentor auratus
• Dermacentor circumgutattus
• Dermacentor halli
• Dermacentor hunteri
• Dermacentor marginatus
• Dermacentor nitens
• Dermacentor occidentali
• Dermacentor parumapterus
• Dermacentor reticulatus - Marsh tick; Ornate cow tick
• Dermacentor silvarum
• Dermacentor variabilis - American dog tick; Wood tick; Eastern Wood tick

• Margaropus Karsch, 1879 (3 species)
• Rhipicentor Nuttall & Warburton, 1908 (2 species)
• Rhipicephalus (c. 80 species)

• Rhipicephalus bursa
• Rhipicephalus camicas
• Rhipicephalus evertsi
• Rhipicephalus pravus
• Rhipicephalus pumilio
• Rhipicephalus pusillus
• Rhipicephalus rossicus
• Rhipicephalus sanguineus
• Rhipicephalus turanicus

Argasidae

• Argasidae C. L. Koch, 1844 (4 genera, c. 200 species) — soft ticks

• Argasinae

• Argas Latreille, 1795

• Ornithodorinae

• Carios Latreille, 1796
• Ornithodoros C.L. Koch, 1837
• Otobius Banks, 1912 (3 species)

Nuttalliellidae

• Nuttalliellidae Schulze, 1935 (1 species)

• Nuttalliella Bedford, 1931

• Nuttalliella namaqua Bedford, 1931

Life cycle

  The life cycle of the hard tick requires one to three years to complete, and may require one, two or three different host animals. The following describes the three-host lifecycle

1. An adult female tick drops off her final host, lays her eggs and dies.
2. Tiny six-legged larvae congregate on grasses or other leaves and stems not far from ground level. Lucky individuals complete that stage after attaching to a host, feeding, and dropping off. The larval stage can cause intense itching on humans, but does not transmit disease.
3. Larvae molt and emerge as the nymph stage, about 1.5 mm long and again climb a grass stem to await a host. The nymph stage also causes intense itching in humans.
4. Engorged nymphs drop off, molt to the adult stage, approximately 3 mm long, mate, and again climb a stem to await a host. Adults are amazingly stealthy on humans in spite of their size, and may not be noticed until they have been attached for a considerable time.

Ticks reproduce sexually, use internal fertilisation and are oviparous. Ticks produce a lot of young but the young are not nurtured.

Ticks as disease vectors

See main article: Tick-borne disease

Ticks are second only to mosquitoes as vectors of human disease, both infectious and toxic.^[1]

Hard ticks can transmit human diseases such as Lyme disease, Rocky Mountain spotted fever, tularemia, equine encephalitis, Colorado tick fever, and several forms of ehrlichiosis. Additionally, they are responsible for transmitting livestock and pet diseases, including babesiosis, anaplasmosis and cytauxzoonosis.

Soft ticks transmit tick-borne relapsing fever spirochetes such as Borrelia turicatae, Borrelia parkeri and Borrelia hermsii.

Generally, tick-borne diseases correspond to a specific tick-host combination, and are limited in their geographical extent. For example, nearly 90% of all Lyme disease (caused by the Borrelia burgdorferi bacterium) cases have been reported in the Northeastern part of the US; ^[2] only specific deer ticks carry that disease.^[3] According to the Rhode Island Department of Health, roughly 70% of people who develop Lyme disease in that part of North America catch it from ticks in their own yard. ^[4]

The West Coast, although originally identified by A.C.Steere as a focus of Lyme disease, has traditionally been viewed as having minimal tick infection rates. In the past, it was believed that the role of the Western Fence Lizard in the California tick life cycle produced adult tick infection rates of only 2-3%. However, a landmark study in 2003 published in The Journal of Medical Entomology by the San Jose State Entomology Department found that the minimum infection rates of the microbe Borrelia burgdorferi in the tick Ixodes pacifica were much higher in Santa Cruz County, up to 17.8% in The Forest of Nisene Marks State Park. This completely transformed traditionally held views of Lyme disease in California as a minimal risk and instead raised the specter of rampant misdiagnosis as the reason for the lower case numbers. Rick Vetter of UC Riverside has shown in published work that tick-induced Lyme disease rashes in California are often misidentified as brown recluse spider bites, when, in fact, brown recluse spiders have never been documented in California.

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.

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.

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 ^[5]. 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. See the Connecticut Agricultural Experiment Station and Connecticut Department of Public Health joint publication "Tick Management Handbook" ^[6] 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. ^[5][7][8][9] For example when the deer population was reduced by 74% at a 248-acre study site in Bridgeport, CT, the number of nymphal ticks collected at the site decreased by 92% ^[5]. lurthermore, the relationship between deer abundance, tick abundance, and human cases of Lyme disease was well documented in the Mumford Cove Community in Groton, CT, 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. (DEP Wildlife Division: Managing Urban Deer in Connecticut 2nd edition June 2007) Deer population management must serve as the main tool in any long-term strategy to reduce human incidences of Lyme disease. ^[10]

A method of reducing deer tick (Ixodes scapularis/dammini) populations - Damminix [2] - 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 [3] 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[4]. 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 Federal 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; see [5].

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. Just 2 birds can clear 2 acres in a single year. However they can be quite noisy, and employers of this method should be prepared for complaints from neighbors.

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 US EPA has made at least one manufacturer of these products (Hartz Mountain Corp., Secaucus, New Jersey, USA), withdraw some products and include strong cautionary statements on others, warning of adverse reactions (http://www.epa.gov/pesticides/factsheets/flea-tick-drops.htm).

Removal

To remove a tick use a small set of tweezers: grab the head, pulling slowly and steadily.[6]. 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.[7] Tiny larval ticks can usually be removed by carefully scraping with a fingernail. 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.

An effective method involves carving the end of a small stick into a flat blade resembling a screwdriver, but with a small notch in the end. This implement is especially useful removing ticks from dogs.

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 clogs the animal's breathing passages and cause it to de-attach 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.[8];[9];[10];[11];[12]

As stated in information about ether's Anesthetic use [13]
"Ether may be used to anesthetize ticks before removing them from an animal or a person's body. The anesthesia relaxes the tick and prevents it from maintaining its mouthpart under the skin."

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.^[11]

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.