|Castor bean tick, Ixodes ricinus|
|18 genera, c. 900 species|
Ticks are small arachnids in the order Ixodida. Along with mites, they constitute the subclass Acarina. Ticks are ectoparasites (external parasites), living by hematophagy on the blood of mammals, birds, and sometimes reptiles and amphibians. Ticks are vectors of a number of diseases, including Lyme disease, Q fever (rare; more commonly transmitted by infected excreta), Colorado tick fever, Rocky Mountain spotted fever, African tick bite fever, tularemia, tick-borne relapsing fever, babesiosis, ehrlichiosis, Tick paralysis and tick-borne meningoencephalitis, as well as bovine anaplasmosis.
Of the three families of ticks, one – Nuttalliellidae – comprises a single species, Nuttalliella namaqua. The remaining two families contain the hard ticks (Ixodidae) and the soft ticks (Argasidae).
Ixodidae (>700 species) are distinguished from the Argasidae by the presence of a scutum or hard shield. In Ixodidae nymphs and adults, a prominent capitulum (head) projects forwards from the body; in the Argasidae, conversely, the capitulum is concealed beneath the body.
The Argasidae contain 193 species, although the composition of the genera is less certain, and more study is needed before the genera can become stable. The currently accepted genera are Antricola, Argas, Nothaspis, Ornithodoros, and Otobius. Though common in North America, they feed rapidly, primarily on birds, and are very rarely found to parasitize land animals or humans.
The family Nuttalliellidae contains only a single species, Nuttalliella namaqua, a tick found in southern Africa from Tanzania to Namibia and South Africa,. It can be distinguished from ixodid ticks and argasid ticks by a combination of characters, including the position of the stigmata, lack of setae, strongly corrugated integument, and form of the fenestrated plates.
Fossilized ticks are common. Recent hypotheses based on total-evidence approach analysis place the origin of ticks in the Cretaceous ( ), with most of the evolution and dispersal occurring during the Tertiary ( ). 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.
Range and habitat 
Tick species are widely distributed around the world, but they tend to flourish more in countries with warm, humid climates, because they require a certain amount of moisture in the air to undergo metamorphosis, and because low temperatures inhibit their development from egg to larva. Ticks of domestic animals are especially common and varied in tropical countries, where they cause considerable harm to livestock by transmission of many species of pathogens and also causing direct parasitic damage.
For an ecosystem to support ticks, it must satisfy two requirements: the population density of host species in the area must be high enough, and humidity must be high enough for ticks to remain hydrated. Due to their role in transmitting Lyme disease, ixodid ticks, particularly I. scapularis, have been studied using geographic information systems (GIS), to develop predictive models for ideal tick habitats. According to these studies, certain features of a given microclimate – such as sandy soil, hardwood trees, rivers, and the presence of deer – were determined to be good predictors of dense tick populations.
Anatomy and physiology 
Ticks, like mites, have bodies which are divided into two primary sections: the anterior capitulum (or gnathosoma), which contains the head and mouthparts; and the posterior idiosoma which contains the legs, digestive tract, and reproductive organs.
Diet and feeding behaviors 
Ticks satisfy all of their nutritional requirements on a diet of blood, a practice known as hematophagy. They extract the blood by cutting a hole in the host's epidermis, into which they insert their hypostome, likely keeping the blood from clotting by excreting an anticoagulant.
Like all arachnids, ticks have eight legs. The legs of Ixodidae and Argasidae are similar in structure. Each leg is composed of six segments: the coxa, trochanter, femur, patella, tibia, and tarsus. Each of these segments is connected by muscles which allow for flexion and extension, but the coxae have limited lateral movement. When not being used for walking, the legs remain tightly folded against the body.
In addition to being used for locomotion, the tarsus of leg I contains a unique sensory organ, the Haller's organ, which can detect odors and chemicals emanating from the host, as well as sensing changes in temperature and air currents.
Life cycle and reproduction 
Both ixodid and argasid ticks undergo three primary stages of development: larval, nymphal, and adult. Ixodid ticks require three hosts, and their life cycle takes at least one year to complete. Up to 3,000 eggs are laid on the ground by an adult female tick. When larvae emerge, they feed primarily on small mammals and birds. After feeding, they detach from their host and molt to nymphs on the ground, which then feed on larger hosts and molt to adults. Female adults attach to larger hosts, feed, and lay eggs, while males feed very little and occupy larger hosts primarily for mating.
Argasid ticks, unlike ixodid ticks, may go through several nymphal stages, requiring a meal of blood each time. Their lifecycles range from months to years. The adult female argasid tick can lay a few hundred to over a thousand eggs over the course of her lifetime. Larvae feed very quickly and detach to molt to nymphs. Nymphs may go through as many as seven instars, each requiring a blood meal. Both male and female adults feed on blood, and they mate off the host. During feeding, any excess fluid is excreted by the coxal glands, a process which is unique to argasid ticks.
Medical issues 
Tick-borne disease 
Tick-borne illnesses are caused by infection with a variety of pathogens, including Rickettsia and other types of bacteria, viruses, and protozoa. Because ticks can harbor more than one disease-causing agent, patients can be infected with more than one pathogen at the same time, compounding the difficulty in diagnosis and treatment. Major tick-borne diseases include Lyme disease, Rocky Mountain spotted fever, relapsing fever, tularemia, tick-borne meningoencephalitis, Colorado tick fever, Crimean-Congo hemorrhagic fever, babesiosis, and cytauxzoonosis. A recent find is Candidatus neoehrlichia mikurensis, a bacterium which causes blood clots; present in 9% of rodents, it mainly affects persons with lowered immune defense, and can be cured with antibiotics.
Tick bites may also induce a delayed allergy to red meat, involving the oligosaccharide, galactose alpha-1,3-galactose: the food-induced reactions, including anaphylaxis, characteristically present several hours after eating in subjects who have experienced a large local reaction to tick bites up to six months earlier.
First aid 
In general, the best way to remove an adult tick is mechanically. To facilitate prompt removal, fine-tipped tweezers can be used to grasp the tick as close to the skin as possible and detach it by applying a steady upward force without crushing, jerking or twisting, in such a way as to avoid leaving behind mouthparts or provoking regurgitation of infective fluids into the wound. Proprietary tick removal tools are also available. It is important to disinfect the bite area thoroughly after removal of the tick. The tick can be stored and, in case of signs or symptoms of a subsequent infection, shown to a clinician for identification purposes together with details of where and when the bite occurred. If the tick's head and mouthparts are no longer attached to its body after removal, a punch biopsy may be necessary to remove any parts left inside the patient.
Population control measures 
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 lifecycle by killing the eggs. However, the US 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.
Deer ticks 
The black-legged or deer tick (Ixodes scapularis) is dependent on the white-tailed deer for reproduction. Larval and nymphal stages (immature ticks that cannot reproduce) of the deer tick feed on birds and small mammals. The adult female tick needs a large three-day blood meal from the deer before she can reproduce and lay her 2000 or more eggs. Deer are the primary hosts for the adult deer ticks, and are key to their reproductive success.
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%. 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 to about 10 deer per square mile (four deer per square kilometer) after two 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.
A 2006 study by Penn State's Center for Infectious Disease Dynamics indicated reducing the deer population in small areas (but not large 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.
See also 
|Wikimedia Commons has media related to: Ixodida|
- "Q fever". Centers for Disease Control. Retrieved November 7, 2010.
- Guglielmone et al. (2010)
- Goddard (2008): p. 80
- Molyneux (1993) p. 6
- Allan (2001)
- Keirans et al. (1976)
- Roshdy et al. (1983)
- de la Fuente (2003)
- Magnarelli (2009)
- Nuttall (1905)
- Wall & Shearer (2001): p. 55
- Goddard (2008): p. 82
- Sonenshine (2005): p. 14
- Nicholson et al. (2009): p. 486
- For Haller's organ, see also: Mehlhorn (2008): p. 582.
- Dennis & Piesman (2005): p. 5
- Aeschlimann & Freyvogel, 1995: p. 182
- Andersson & Råberg (2011)
- Bianca Nogrady (May 10, 2008). "One tick red meat can do without". The Australian. Retrieved October 17, 2011.
- Saleh et al. (2012)
- "Correct tick removal". Borreliosis and Associated Diseases Awareness UK. Retrieved March 30, 2012.
- "Tick removal". LDA. Retrieved March 30, 2012.
- "Tick removal". Centers for Disease Control and Prevention. Retrieved March 30, 2012.
- Zuber & Mayeaux (2003), p. 63
- Dennis & Piesman, 2005: p. 3
- Duffy et al. (1992)
- "Hartz flea and tick drops for cats and kittens to be phased out". Environmental Protection Agency. Archived from the original on January 11, 2011. Retrieved September 16, 2011.
- Stafford (2007)
- Rand et al. (2004)
- Walter et al. (2002)
- Wilson et al. (1990)
- Kilpatrick & LaBonte (2007)
- "Deer-free areas may be haven for ticks, disease". Science Daily. September 4, 2006.
- Aeschlimann, André & Thierry A. Freyvogel (1995). "Biology and distribution of ticks of medical importance". In Jürg Meier & Julian White. Handbook of Clinical toxicology of Animal Venoms and Poisons 236. CRC Press. pp. 177–189. ISBN 978-0-8493-4489-3.
- Allan, Sandra A. (2001). "Ticks (Class Arachnida: Order Acarina)". In William M. Samuel, Margo J. Pybus & A. Allan Kocan. Parasitic Diseases of Wild Mammals. Wiley-Blackwell. pp. 72–106. ISBN 978-0-8138-2978-4.
- Andersson, Martin & Lars Råberg (2011). "Wild rodents and novel human pathogen Candidatus Neoehrlichia mikurensis, southern Sweden". Emerging Infectious Diseases 17 (9): 1716–1718. doi:10.3201/eid1709.101058.
- Dennis, David T. & Joseph F. Piesman (2005). "Overview of tick-borne infections of humans". In Jesse L. Goodman et al. Tick-borne Diseases of Humans. ASM Press. pp. 3–11. ISBN 978-1-55581-238-6.
- Duffy, David Cameron, Randall Downer & Christie Brinkley (1992). "The effectiveness of Helmeted Guineafowl in the control of the deer tick, the vector of Lyme disease" (PDF). Wilson Bulletin 104 (2): 342–345.
- de la Fuente, José (2003). "The fossil record and the origin of ticks (Acari: Parasitiformes: Ixodida)". Experimental and Applied Acarology 29 (3–4): 331–334. doi:10.1023/A:1025824702816. PMID 14635818.
- Goddard, Jerome (2008). "Tick-borne diseases". Infectious Diseases and Arthropods. Springer. ISBN 978-1-60327-399-2.
- Guglielmone, Alberto A., Richard G. Robbing, Dmitry A. Apanaskevich, Trevor N. Petney, Agustín Estrada-Peña, Ivan G. Horak, Renfu Shao & Stephen C. Barker (2010). "The Argasidae, Ixodidae and Nuttalliellidae (Acari: Ixodida) of the world: a list of valid species names" (PDF). Zootaxa 2528: 1–28.
- Keirans, James E., Carleton M. Clifford, Harry Hoogstraal & Emmett R. Easton (1976). "Discovery of Nuttalliella namaqua Bedford (Acarina: Ixodoidea: Nuttalliellidae) in Tanzania and redescription of the female based on scanning electron microcopy". Annals of the Entomological Society of America 69 (5): 926–932.
- Kilpatrick, Howard J. & Andrew M. LaBonte (June 2007). Managing Urban Deer in Connecticut: a Guide for Residents and Communities (PDF) (2nd ed.). Connecticut Department of Environmental Protection.
- Magnarelli, Louis A. (2009). "Global importance of ticks and associated infectious disease agents". Clinical Microbiology Newsletter 31 (5): 33–37. doi:10.1016/j.clinmicnews.2009.02.001.
- Mehlhorn, Heinz & Philip M. Armstrong, ed. (2001). "Ticks". Encyclopedic Reference of Parasitology. Springer. pp. 608–638. ISBN 978-3-540-66819-0.
- Molyneux, D. H. (1993). "Vectors". In Francis E. G. Cox. Modern Parasitology: a Textbook of Parasitology (2nd ed.). Wiley-Blackwell. pp. 53–74. ISBN 978-0-632-02585-5.
- Nicholson, William L. et al. (2009). "Ticks (Ixodida)". In Gary Mullen & Lance Durden. Medical and Veterinary Entomology. Academic Press. pp. 483–532. ISBN 978-0-12-372500-4.
- Nuttall, George H. F. (1905). "Ticks and tick-transmitted diseases". Transactions of the Epidemiological Society of London 24: 12–26.
- Rand, Peter W., Charles Lubelczyk, Mary S. Holman, Eleanor H. Lacombe & Robert P. Smith, Jr. (2004). "Abundance of Ixodes scapularis (Acari: Ixodidae) after complete removal of deer from an isolated offshore island, endemic for Lyme disease". Journal of Medical Entomology 41 (4): 779–784. doi:10.1603/0022-2585-41.4.779. PMID 15311475.
- Roshdy, Mohamed A., Harry Hoogstraal, Abdulelah A. Banaja & Samir M. El Shoura (1983). "Nuttalliella namaqua (Ixodoidea: Nuttalliellidae): spiracle structure and surface morphology". Parasitology Research 69 (6): 817–821. doi:10.1007/BF00927431.
- Saleh, Hana, Scott Embry, Andromeda Nauli, Seif Atyia & Guha Krishnaswamy (2012). "Anaphylactic reactions to oligosaccharides in red meat: a syndrome in evolution". Clinical and Molecular Allergy 10 (5). doi:10.1186/1476-7961-10-5. PMID 22397506.
- Sonenshine, Daniel E. (2005). "The biology of tick vectors of human disease". In Jesse L. Goodman et al. Tick-borne Diseases of Humans. ASM Press. pp. 12–36. ISBN 978-1-55581-238-6.
- Stafford, Kirby C., III (2007). Tick Management Handbook: an Integrated Guide for Homeowners, Pest Control Operators, and Public Health Officials for the Prevention of Tick-associated Disease (PDF). New Haven, Connecticut: The Connecticut Agricultural Experiment Station.
- Wall, Richard & David Shearer (2001). "Ticks (Acari)". Veterinary Ectoparasites: Biology, Pathology, and Control. John Wiley & Sons. pp. 55–82. ISBN 978-0-632-05618-7.
- Walter, W. David, Peter J. Perkins, Allen T. Rutberg & Howard J. Kilpatrick (2002). "Evaluation of immunocontraception in a free-ranging suburban white-tailed deer herd". Wildlife Society Bulletin 30 (1): 186–192. JSTOR 3784652.
- Wilson, Mark L., Anne M. Ducey, Thomas S. Litwin, Thomas A. Gavin & Andrew Spielman (1990). "Microgeographic distribution of immature Ixodes dammini ticks correlated with deer". Medical and Veterinary Entomology 4 (2): 151–159. doi:10.1111/j.1365-2915.1990.tb00273.x. PMID 2132979.
- Zuber, Thomas J. & E. J. Mayeaux (2003). "Tick removal". Atlas of Primary Care Procedures. Lippincott Williams & Wilkins. pp. 63–67. ISBN 978-0-7817-3905-4.
Further reading 
- Bruin, Jan & L. P. S. van der Greest, ed. (2009). Diseases of Mites and Ticks. Springer. ISBN 978-1-4020-9694-5.
- Cunha, Burke A. (2000). Tickborne Infectious Diseases: Diagnosis and Management. CRC Press. ISBN 978-0-8247-0310-3.
- Service, M. W. (2004). "Soft ticks (Argasidae)". Medical Entomology for Students. Cambridge University Press. pp. 213–221. ISBN 978-0-521-54775-8.
- Service, M. W. (2004). "Hard ticks (Ixodidae)". Medical Entomology for Students. Cambridge University Press. pp. 222–236. ISBN 978-0-521-54775-8.
- Sonenshine, Daniel E. (1993). Biology of Ticks. Vols. 1 & 2. Oxford University Press. ISBN 978-0-19-508431-3.