Ticks

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Ticks
Adult hedgehog tick (Ixodes hexagonus)

Adult hedgehog tick ( Ixodes hexagonus )

Systematics
Trunk : Arthropod (arthropoda)
Sub-stem : Jawbearers (Chelicerata)
Class : Arachnids (arachnida)
Subclass : Mites (acari)
Superordinate : Parasitiformes
Order : Ticks
Scientific name
Ixodida
Leach , 1815
Familys

The ticks (Ixodida) are an order of the mites (Acari), which are assigned to the parent Parasitiformes . The largest types of mites are found among ticks. All species are blood-sucking ectoparasites on vertebrates , including humans. Many types of ticks are important carriers of disease . In 2004 around 900 species of ticks were known worldwide.

features

As with most species of mite, the body of the tick consists of two movable sections separated from each other. The front section, generally called Gnathosoma for mites , has the different name of capitulum for ticks (for historical reasons). This section corresponds to what is commonly referred to as the tick's head . The rest of the trunk is called an idiosoma. The anterior section, the podosoma, which supports the legs, merges without a sharp border into the posterior section, the opisthosoma. On the back section of the capitulum, many ticks have two conspicuous pore fields that, according to various views, serve either as glands or as sensory organs. The four pairs of legs sit on the side of the idiosoma. The legs consist of six clearly separated segments (named Coxa- Trochanter-Femur-Patella or Genu-Tibia-Tarsus). At the tip of the tarsus there are two claws and the ticks (and the larvae of the leather ticks) have an adhesive pad (pulvillus) to hold onto smooth surfaces. On the side of the idiosoma there are two openings in the trachea, which are called stigmas and are air-filled channels that enlarge the body surface for breathing. Especially in shield ticks, they usually sit within a sclerotized and conspicuously sculptured field of stigmas. Many types of ticks have small, inconspicuous eyes that sit in pairs on the upper side of the body (dorsal) in the case of the tick, but z. B. absent in the genus Ixodes . There may be a higher number of leather ticks that sit on the edge of the underside of the body (ventral). In at least one type of tick, the camel tick Hyalomma dromedarii , optical host finding ( scototaxis ) is proven by perceiving the silhouette of the host.

The two families of Schildzecken and Lederzecken differ in that the shield ticks have the name-giving shield ( scutum ) that sits on top (dorsal) of the idiosoma. In many species of ticks, such as the common wood tick, it covers the entire trunk of the male, but only about half of the female. A shield is missing from the leather ticks. In addition, in leather ticks, the capitulum with the mouthparts sits slightly on the abdomen (ventral) on the body, so that it is not visible when viewed from above.

Mouthparts and suction process

The main characteristic of the ticks are the mouthparts on the front of the capitulum. These are peculiarly redesigned for the blood-sucking way of life. On the outside there are two four-part buttons (palps), which are sensory organs and do not take part in the suction process. In the rest position, they often envelop the actual mouthparts. In the center sits a proboscis called a hypostome , which often has teeth that act as barbs. The two chelicerae sit on the upper side (dorsal) and usually not visible from below . These consist of a two-part shaft, which is stretched forward parallel to the hypostome and which is immovable with a broad base on the basal part of the capitulum. At the top they have several movable tooth-shaped protrusions, called chelicerene fingers. During the sucking process, the tick scratches the skin with its chelicerae and then pushes the hypostome into the wound. Contrary to popular belief, the hypostome is not a hollow proboscis: the mouth opening is basal to it on the broader base of the capitulum. The hypostome can carry a sunken food channel. This process is commonly referred to as a tick bite, but is correct tick bite .

During the sucking process, the animal creates a wound with its mouth parts by tearing open tissue with small blood capillaries. The blood that collects here is then sucked up (so-called pool feeder ). Long-nosed animals (prostriata) such as the common wood tick anchor themselves during the sucking process mainly with the mouthparts, short-nosed animals (metastriata) like the Dermacentor species excrete a glue-like or putty-like substance for this purpose. The sucking process is relatively short with the leather ticks, about 30 to 60 minutes, except for the larvae. In the case of the ticks, it can last for many days to weeks. The body of the female tick can swell to twenty times its original volume and one hundred times its weight; in addition to the stretching of the cuticle, real growth processes are also involved. With the leather ticks, less blood, usually about five times the body volume and ten times the weight, is absorbed during a sucking process.

During the suction process, the tick releases saliva into the wound. In the species investigated so far, this contains many hundreds of different proteins , most of which were not found in any other group of animals. The most important function of saliva is to prevent blood platelets from clumping together , which would otherwise lead to wound closure. A number of enzymes intervene at various points in the signal cascade. Further blood clotting is also suppressed in this way. In addition, inflammatory reactions are suppressed (e.g. by prostaglandins ) and the sensation of pain is inhibited in order to avoid defensive reactions on the part of the host. Inhibitors effective against hormones and signal substances such as histamine , serotonin and bradykinin can sometimes achieve several of these purposes in parallel. The saliva released can contain bacteria, viruses and other pathogens that make the tick bite particularly at risk. Although tick saliva generally avoids the function of the body's own immune system at the puncture site, in rare cases immediate allergic reactions can occur in humans. The immunomodulatory relationships between parasite and host are extremely complex. After repeated contact with ticks, the immune defense can increase sharply, but this is species-specific because tick species have developed host-specific immunomodulators . This can lead to unexpected interrelationships. For example, mice were immune to tick borreliosis if they had previously been stung by uninfected ticks several times. Tick ​​paralysis , in which a substance acting as a neurotoxin can inhibit the motor nerves, which continues from the puncture site, is rare, but life-threatening .

After an extensive meal of blood, female ticks in particular can grow to a size of up to 3 cm.

  • male tick

  • slightly soaked tick

  • Soaked tick (from below)

  • Soaked tick (from above)

  • Mating: The smaller male lies belly to belly under the much larger female.

  • Mating preparation. The smaller male pushes his chelicerae into the sexual opening of the female

distribution

Chelicerae of the common wood tuck ( Ixodes ricinus )

Ticks are widespread worldwide and can be found wherever their host species live. The distribution of the individual species depends on the distribution of their respective hosts and also on environmental factors such as temperature and humidity. Most tick species have one or more preferred hosts, but can also suck blood from other hosts if there is a lack of food. About twenty types of ticks occur in Germany, some of them very rarely or possibly only temporarily introduced. The ixodidae Ixodes Ricinus ( Ixodes ricinus ) is the German tick species that affects most people. Other common species of tortoiseshell tick are here e.g. B. the hedgehog tick ( Ixodes hexagonus ), the sheep tick ( Dermacentor marginatus ), in southern Germany also the alluvial forest tick ( Dermacentor reticulatus ). A number of other species live almost exclusively on birds or are very rare and almost never pass to humans. The most common species worldwide that parasitizes on humans is the brown dog tick ( Rhipicephalus sanguineus ), which cannot live permanently in Germany due to insufficient heat.

Most species of the leather tick family are restricted to the tropics and subtropics . In Central Europe, the species Argas vespertilionis lives on bats . The most common species, however, is the pigeon tick Argas reflexus , which lives on city ​​pigeons and , more rarely, on other bird species, in Central Europe only in houses and other buildings.

behavior

In principle, there are two strategies for finding a host among the tick species:

  • Lurkers climb onto a plant (e.g. a blade of grass or a bush) and hold on with their back legs. They stretch the front pair of legs in a characteristic pose far outwards so that a T-shape results. As soon as a potential host touches them, they hold onto it. One of the lurkers is z. B. the common wooden trestle.
  • Hunters actively move forward in search of host organisms. At 5–8 meters per hour, they are faster than Roman snails (4.2 meters per hour).

Various chemical senses are used to find the host, especially carbon dioxide sensors, which are located in a special organ on the last leg ( Haller's organ ). The brown dog tick is an example of a hunter.

In males, a blood meal usually lasts only a few days, as they only need blood for their own nutrition. You can suck blood multiple times while waiting for a female. The females are not only dependent on blood for their own nutrition, but also for egg formation and therefore need a much larger amount of blood. Your blood meal can go on for weeks undisturbed.

Soaked tick in a dog's fur

The ticks use their Haller organ to find the food victim. This pit-shaped chemoreceptor , which is equipped with sensory bristles, is located on the last leg element (the tarsus ) of the first pair of legs and can detect substances such as ammonia , carbon dioxide , lactic acid and, above all, butyric acid , which are given off by the respective host animals through breath and sweat . In the lurking position (the front pair of legs is stretched forward with a slight swing, with the three back pairs of legs they clasp their hide), this organ is stretched out so that the ticks can better receive the sensory stimuli. The waiting ticks immediately switch from the waiting position (the folded forelegs are close to the body) to the lurking position when they notice from olfactory stimuli, changes in light - especially from light to dark - or vibrations that a host may be approaching. They then cling to everything that touches their respective whereabouts and then often crawl around the body of animals and humans for up to several hours until they have found a suitable puncture site. Ticks are very picky and prefer slightly moist, warm and well-perfused, thin skin. In humans , the hollows of the knees , the hairline, the groin and the fine skin behind the ears are particularly popular targets.

After the blood meal is finished, they let themselves fall off their host and the females then look for a protected spot on the ground in order to lay eggs straight away. Egg-laying can take several days, with an egg being laid about every ten minutes. After one has emerged from the abdominal opening, it is guided past a gland with the mouth parts and provided with a protective layer that protects the fresh egg from drying out. When the ticks lay eggs, thousands of eggs are produced (up to 20,000 in the genera Hyalomma and Amblyomma ), after which the female dies.

Leather tick species, which have to suckle on their hosts much more often than shield ticks, can therefore be found almost exclusively in their hosts' nests, buildings or hiding places (few tropical species are active hunters). In contrast to the ticks, the female eats blood meals several times in a row and then lays eggs each time (up to seven times). The number of eggs is smaller every time. They withdraw into crevices and corners after each blood meal and then wait until a host comes within range again. Species of the large genus Ornithodoros that infest migratory birds can wait for the time in the nest while their host is absent. It is reported that leather ticks can survive waiting for many years without eating. Ornithodoros papillipes holds the record at the age of eleven. In the case of building-dwelling species such as the pigeon tick, this can also lead to major problems for humans.

Life cycle

After hatching, like all mites, ticks always go through three stages of development and two molting processes: larva (with six legs), nymph (with eight legs) and adults (the adult males and females). The sexual characteristics only develop in the adult phase.

The Argasidae ( leather ticks ) have several, from two to eight nymph stages. Every larva and nymph is dependent on the blood of a host . The same host species is often attacked in all stages. In the case of leather ticks, fertilization of the female takes place away from the host in the environment (usually in the host's burrow or nest). The animals find each other through signal substances ( pheromones ). These often have an effect on older nymphs. A substance that acts as a pheromone is the guanine contained in the feces .

Size comparison of a male tick with a match head
Size comparison length × width
Larvae
(6 legs) 		Nymph
(8 legs) 		Adult (male or female)
(8 legs) 		fully soaked adult
(8 legs)
Larvae nymph Adult tick (male or female) female Adult (soaked)
0.5mm x 0.4mm 1.2mm x 0.85mm 3.8 mm x 2.6 mm 13.2 mm x 10.2 mm

The Ixodidae ( tick ticks ) only have one nymph stage. In many species, the animals change host species between the various stages, often with increasing size. However, there are species in which the moulting from larva to nymph takes place on the host, sometimes even both moults, so that only the mature female leaves the host (two- and one-host species, e.g. genus Rhipicephalus ). In many species, larvae and nymphs remain in the host's burrow or camp. All three stages are less common in the wild. In the case of the common ram , z. B. from the egg the six-legged larva. This looks for a suitable intermediate host (rodent) after just a few days , sucks in there and takes in blood within two to three days. After suckling, it can fall off and after a few months it sheds its skin into the first eight-legged nymph, around 1.5 to 2 mm in size. This now again looks for a larger host (second intermediate host - cat) and also sucks blood there. Under Central European climatic conditions, most nymphs that have molted in summer or autumn do not immediately look for a new host for a blood meal, but instead enter a dormant stage at temperatures below 7 ° to 8 ° until next spring (can in particular mild winters also fail). Only after this break do they look for a host and then another molt to the adult takes place. The adult animal then attacks the ultimate host (humans, cattle). Mating takes place on the host, after which the male dies. If mating does not occur immediately, the female remains on the host half-sucked and waits for a male. The female drops after this last blood meal and lays her eggs shortly afterwards.

Ticks as a disease carrier

When tick bites, ticks often transmit pathogens between hosts due to their way of life , but without becoming sick themselves. There are more types of pathogens in question than any other group of parasitic animals. People are also affected by diseases such as Lyme disease , early summer meningoencephalitis ( TBE ), babesiosis , ehrlichiosis , rickettsioses or neoehrlichiosis .

The most important vectors in Central Europe are the species of the genus Ixodes with the most common native species, the common wood tick ( Ixodes ricinus ), as well as the genera Rhipicephalus , Dermacentor , Haemaphysalis , Amblyomma and from the family of leather ticks the genera Argas and Ornithodorus . While ticks in the past only posed a danger in the summer half of the year, as they hibernated in the winter months , they are now - due to global warming - active all year round in mild winters.

For more detailed information on this, see tick bite .

  • Warning notice in a forest area in Mecklenburg-Western Pomerania

  • Deer tick sucking on human leg

  • Wandering redness as a result of a tick bite with borreliosis infection

Natural enemies and habitat restrictions

The following have been identified as natural enemies of ticks:

The ecological demands of the various tick species and, accordingly, their habitat are very different. Many types, e.g. B. the common ram, are very humid and dry up quickly in direct sunlight. Although ticks can survive even severe frosts unscathed, long periods of cold weather in particular are lethal for many species and limit the range to the north. Individual years with different weather conditions, e.g. Mild winters, for example, can have a major impact on population size.

At the moment there is a discussion about how the current climate change will affect the spread of ticks in Central Europe or North America. Some tick species have been shown to be able to expand their range to the north (e.g. Ixodes ricinus in Scandinavia), while the effects of others are controversial. There are always extensive interrelationships, e.g. B. between temperature and humidity to be charged.

Systematics

Sister group of ticks are probably mites of the order Holothyrida . These suck out dead animals (especially arthropods).

The ticks themselves are divided into three families and there are more than 850 species worldwide.

Fossil evidence

Fossil evidence is extremely rare. Almost all fossil ticks were found in Cretaceous and Tertiary amber . The oldest finds are around 100 million years old ( Birmite and New Jersey amber ). The Cretaceous fossils are larvae; all adult ticks found so far come from amber of tertiary deposits (Eocene Baltic amber, Miocene Dominican amber ). In research on the evolution of ticks, there is consensus that their development began much earlier than the oldest fossils suggest. However, there is disagreement over the question of whether this was already the case in the Devonian or in the Triassic and whether the first hosts were amphibians or reptiles.

literature

  • The disease carrier tick - Lyme borreliosis and TBE , BgVV , Verl. Im Kilian, Marburg 1997 [1]
  • Hans-Peter Wirtz: Ticks as a disease carrier: what to do if you get a bite? In: Biology in Our Time. Vol. 31, No. 4, 2001, ISSN  0045-205X , pp. 229-238.
  • Johannes Eckert, Karl Theodor Friedhoff, Horst Zahner, Peter Deplazes: Textbook of Parasitology for Veterinary Medicine. Enke, Stuttgart 2008, ISBN 3-8304-1032-8 .

Web links

Commons : ticks  - collection of images, videos and audio files
Wiktionary: Zecke  - explanations of meanings, word origins, synonyms, translations

Individual evidence

  1. ^ Systematics from ticks: SC Barker, A. Murrell: Systematics and evolution of ticks with a list of valid genus and species names ( Memento of November 8, 2011 in the Internet Archive ). In: Parasitology. No. 129, 2004, pp. 15-36, PMID 15938503 .
  2. ↑ Martin Kaltenrieder: Scototaxis and target perception in the camel tick Hyalomma dromedarii. In: Experimental and Applied Acarology. 1990, Vol. 9, No. 3-4, pp. 267-278, doi: 10.1007 / BF01193433 .
  3. ↑ Overview in: IM Francischetti, A. Sa-Nunes, BJ Mans, IM Santos, JM Ribeiro: The role of saliva in tick feeding. In: Frontiers in Bioscience. 2009, No. 14, pp. 2051-2088, PMID 19273185 .
  4. ↑ Albin Fontaine, Ibrahima Diouf, Nawal Bakkali, and others. a .: Implication of haematophagous arthropod salivary proteins in host-vector interactions. In: Parasites & Vectors. 2011, No. 4, p. 187 ( open access ).
  5. ↑ SK Wikel, RN Ramachandra, DK Bergman, TR Burkot, J. Piesman: Infestation with pathogen-free nymphs of the tick Ixodes scapularis induces host resistance to transmission of Borrelia burgdorferi by ticks. In: Infection and Immunity . 1997, Vol. 65, No. 1, pp. 335-338.
  6. ↑ Fishing is sooo nice - but you should know something about ticks ( Memento from April 24, 2014 in the Internet Archive ) Tips on how to behave with ticks.
  7. ↑ YS Balashov: Interaction between blood-sucking arthropods and Their hosts, and its influence on vector potential. In: Annual Revue of Entomology. 1984, No. 29, pp. 137-156.
  8. ↑ ticks. In: Schutzgemeinschaft Deutscher Wald . Retrieved October 31, 2019 .
  9. ↑ Answers to frequently asked questions about ticks, tick bites and infections. In: Robert Koch Institute . August 12, 2019, accessed October 31, 2019 .
  10. ↑ Hans Dautel, Cornelia Dippel, Daniel Kämmer, Anita Werkhaus, Olaf Kahl: Winter acitivy of Ixodes ricinus in a Berlin forest area. Lecture script of the Federal Environment Agency conference Vector-Borne Diseases: Impact of Climate Change on Vectors and Rodent Reservoirs. Berlin, September 27 & 28, 2007.
  11. ^ W. Reuben Kaufman: Gluttony and sex in female ixodid ticks: How do they compare to other blood-sucking arthropods? In: Journal of Insect Physiology. 2007, Vol. 53, No. 3, pp. 264-273, doi: 10.1016 / j.jinsphys.2006.10.004 .
  12. ↑ University of Zurich : New tick disease in Switzerland. ( Memento of July 11, 2014 in the Internet Archive ) Media release of October 31, 2012 On: mediadesk.uzh.ch ; last accessed on June 12, 2014.
  13. ↑ Overview in: Augustin Estrada-Pena, Frans Jongjean: Ticks feeding on humans: a review of records on human-biting Ixodoidea with special reference to pathogen transmission. In: Experimental and Applied Acarology. September 1999, Vol. 23, No. 9, pp. 685-715, PMID 10581710 .
  14. ↑ What dangers from parasites are lurking where in Europe? On: parasitenfrei.de ; last accessed on June 12, 2014.
  15. ↑ Peter Berthold : Bienenfresser in Iceland, great egret in Siberia. How birds react to climate change around the world. In: Jochem Marotzke , Martin Stratmann (Hrsg.): The future of the climate. New insights, new challenges. A report from the Max Planck Society. Beck, Munich 2015, ISBN 978-3-406-66968-2 , pp. 23–34, pp. 33f.
  16. ↑ DGMEA eV conferences: report of the 13th session of the Working Group of Medical Entomology Arachno (IMAD eV) in Stuttgart / Hohenheim 29-30.9.2005 .
  17. ↑ Deutschlandfunk : With Parasites Against Bloodsuckers , March 27, 2018, loaded on July 15, 2019
  18. ↑ Kathrin Hartelt et al .: Biological control of the tick Ixodes ricinus with entomopathogenic fungi and nematodes: Preliminary results from laboratory experiments . In: International Journal of Medical Microbiology 2008, Volume 298, Supplement 1, pp. 314-320, doi: 10.1016 / j.ijmm.2007.10.003 .
  19. ↑ Keiji Takasu and Satoshi Nakamura: Life history of the tick parasitoid Ixodiphagus hookeri (Hymenoptera: Encyrtidae) in Kenya . In: Biological Control 2008, Volume 46, No. 2, pp. 114–121, doi: 10.1016 / j.biocontrol.2008.04.013 .
  20. ^ JS Gray, H. Dautel, A. Estrada-Pena, O. Kahl, E. Lindgren: Effects of Climate Change on Ticks and Tick-Borne Diseases in Europe. In: Interdisciplinary Perspectives on Infectious Diseases. 2009, Vol. 2009, Article ID: 593232, doi: 10.1155 / 2009/593232 .
  21. ↑ JSH clogs, WC Black, Keiran JE, DE Norris: Systematics and biogeography of hard ticks, a total evidence approach. In: Cladistics. 2000, No. 16, pp. 79-102, doi: 10.1111 / j.1096-0031.2000.tb00349.x .
  22. ^ GW Krantz, David Evans Walter (Ed.): A Manual of Acarology. Third edition, Texas Tech University Press, Lubbock (Texas) 2009, ISBN 978-0-89672-620-8 , pp. 111-117.
  23. ^ Nave, Guglielmone, Mangold: An overview of systematics and evolution of ticks. - In: Frontiers in Bioscience 14 (8): 2857-77, Irvine (USA) 2009.
  24. ↑ Gröhn: inclusions in Baltic amber. Kiel 2015.