Taxonomy
Ticks are members of the same phylum (Arthropoda) of the animal kingdom as insects, however are in a different class.
The subphylum Chelicerata includes the class Arachnida, which again contains several subclasses. The subclass Acari (syn. Acaria, Acarina, Acarida) includes ticks.
A characteristic of the Acarines is the extreme fusion of body segments, in contrast to the known three body segments head, thorax and abdomen in insects.
Taxonomy of ticks
| Kingdom: | Animalia |
| Phylum: | Arthropoda |
| Class: | Arachnida |
| Subclass: | Acaria (Acari, Acarina, Acarida) |
| Order: | Anactinotrichidea (= Parasitoformes) |
| Suborder: | Ixodida (= Metastigmata) |
| Family |
Ixodidae (Hard Ticks) |
The Acari are subdivided into the order Parasitiformes and Acariformes.
The order Parasitiformes to which ticks belong have stigmatal pores on the podosoma part (leg-bearing portion) and free articulated coxae (Sonenshine, 1991).
Their suborder is Metastigmata, as their stigmen can be found behind coxa III or behind coxa IV. Its members are obligate blood-sucking parasites which have the following common features:
- Haller's organ - a complex sensory organ, on tarsus I
- Ventral toothed hypostome
- Chelicera of only two joints
- Peritreme around the stigmen
The order Metastigmata comprises three families: the Ixodidae (hard ticks), the Argasidae (soft ticks), and the Nuttalliellidae.
The Nuttalliellidae are represented only by a single species, Nutalliella namaqua; found in South and South-West Africa as a parasite of small mammals. Thus, the two tick families of relevance are Ixodidae (hard ticks) and Argasidae (soft ticks), (Pfister, 2006; Sonenshine, 1991).
The accurate identification of tick species is an important factor in the detection and diagnosis of tick-borne diseases and is a prerequisite for tick control (Cupp, 1991).
Hard Ticks
The family Ixodidae is by far the largest and economically most important tick family with 13 genera and approximately 650 species (Sonenshine, 1991).
The main attribute of this family is a plain dorsal sclerotised scutum or shield, which distinguishes these ticks from other families. This sclerotised plate covers the entire dorsal surface of the male, but only one third of the female's dorsal surface.
The size of the scutum remains constant during the feeding of the female, thus covering an increasingly smaller part of the body with increasing engorgement.
Eyes, if present, occur on the postero-lateral margins of the scutum.
Also typical is a strong build hypostome with robust teeth, which work as barbsand prevent easy detachment. This led to the name of the family (greek: Ixos = glue) (Kimmig et al., 2000).
In all ixodid ticks, the palps contain 4 segments; the tiny terminal (4th) segment (with sensory sensillae) is retractable and found in a cavity on the ventral surface of segment III.
The mouthparts include the paired chelicerae, the segmented palps, and the ventrally situated, toothed hypostome, all mounted on the basis capituli (Sonenshine, 1991; Mehlhorn, 2001). Characteristically, in hard ticks, the capitulum is visible from a dorsal view.
SEM-micrograph of mouth parts of ixodid tick
Hard ticks can be differentiated by the shape of the basis capituli and by the form of anal grooves. The peritreme or groove is big and clearly visibly around the stigmal plate. Grooves are deep, linear depressions in the body cuticle, usually on the ventral surface.
Soft Ticks
The family Argasidae comprises 5 genera (Argasinae (e.g., Argas reflexus, A. vespertilionis), Ornithodorinae (e.g., Ornithodorus hermsi, O. coriaceus, O. moubata), Otobinae (e.g., Otobius megnini), Antricolinae, Nothoaspinae) with approximately 170 species.
Soft ticks are inornate and have a granulated leathery appearance with an oval or pear-shaped outline. They lack a scutum but most species bear a centrally located dorsal plate which is covered by tiny mammillae, ridge structures that protrude above the cuticle surface. Subcircular depressions termed discs, representing sites of muscle attachment, occur in characteristic patterns over the dorsal and ventral surface. In the larvae, an oval dorsal shield is usually present, but this structure should not be confused with the ixodid scutum, which always located on the anterior part of the body.
Male and female dimorphisms is distinguishable only by the appearance of the genital pore.
In adults and nymphs, the capitulum is recessed ventrally, subterminal, hidden from a dorsal view.
Eyes, when present, occur on the lateral surface of the body. The ventral organ of unknown function appears as a broad transverse ridge posterior to the anus. Spiracles occur on the supracoxal folds between the coxae of leg III and IV.
SEM-micrograph of argasid ticks; dorsal and ventral view. Note the mouthparts only easily visible from the ventral side.
Distribution
Approximately 850 tick species have been described worldwide.
The family Ixodidae (hard ticks) is by far the largest and economically most important family with 13 genera and approximately 650 species.
Rhipicephalus sanguineus, the brown dog tick is the only species of worldwide relevance for dogs, while all other companion animal tick species are of very different geographic relevance.
Distribution of hard tick (Ixodidae) species of dogs and cats
| Region | Latin Name | Common Name |
|---|---|---|
| North America |
Amblyomma americanum Amblyomma maculatum Dermacentor variabilis Dermacentor andersoni Ixodes pacificus Ixodes scapularis (dammini) Rhipicephalus sanguineus Otobius megnini |
Lone Star tick Gulf Coast tick American Dog tick Rocky Mountain Wood tick Western Black-legged tick Black-legged tick Brown dog tick, Kennel tick Spinose ear tick |
| South America | Rhipicephalus sanguineus | Brown dog tick, Kennel tick |
| Europe |
Ixodes ricinus Ixodes canisuga Ixodes hexagonus Ixodes persulcatus Rhipicephalus sanguineus Rhipicephalus bursa Rhipicephalus turanicus Rhipicephalus pusillus Dermacentor reticulatus Dermacentor marginatus Haemaphysalis punctata Haemaphysalis concinna Hyalomma marginatum |
Castor bean tick, sheep tick, wood tick Fox tick, forest tick Hedgehog tick Taiga tick Brown dog tick, Kennel tick
Marsh tick, Meadow tick, Ornate dog tick Ornate sheep tick Red sheep tick Bush tick, Relict tick Bont-legged tick |
| Asia |
Haemaphysalis longicornis Rhipicephalus sanguineus |
Asian longhorned tick, Bush tick Brown dog tick, Kennel tick |
| Australia |
Amblyomma triguttatum Bothricroton sp. Haemaphysalis bancrofti Haemaphysalis longicornis Ixodes cornuatus Ixodes holocyclus Ixodes tasmani Rhipicephalus sanguineus |
Kangaroo tick
Asian longhorned tick, Bush tick Tasmanian paralysis tick Paralysis tick
Brown dog tick, Kennel tick |
| Africa | Rhipicephalus sanguineus | Brown dog tick, Kennel tick |
Many of these hard tick species are relevant as carriers of tick-borne pathogens, and of veterinary and medical importance due to their capability of disease transmission.
Spread of ticks and tick-borne diseases
Ticks and the diseases they transmit have a zoogeographical range restricted by (wild) host movement and climatic factors. However, the increased mobility of pets has resulted in rapid extension of the zoogeographical ranges for many tick species and thus tick-transmitted diseases. The range is also increasing due to the fact that tick species are finding niches in different climatic conditions. Examples for the increasing spread of ticks and tick-borne diseases are reported from different countries:
- The Ornate Cow tick, Dermacentor reticulatus, has in Germany entered large parts of the country over the last twenty years and with it babesiosis caused by Babesia canis, a potentially life-threatening CVBD of dogs. Equally first cases of babesiosis have been recorded in the UK, a country thought to have been free of endemic infections, though foci endemic of D. reticulatus were known to be present. Loosened animal quarantine regulations in the UK may have facilitate the spread.
- Hyalomma marginatum and Hyalomma rufipes, which are mainly distributed in southern Europe, Africa and middle-eastern Asia and are well-known vectors of Crimean Congo hemorrhagic fever (CCHF) virus and other viruses as well as Rickettsia aeschlimannii have in recent years been found sporadically in Germany, but do not belong to the autochthonous tick fauna.
- In the USA, the American Dog tick, Dermacentor variabilis, a major vector of Rocky Mountain spotted fever (RMSF), has reached the North-East of the USA. Climate change has been discussed as one major reason.
References
Introduction
Hoogstraal H, Kim KC: Tick and mammal coevolution, with emphasis on Haemaphysalis. In: Kim KC: Coevolution of parasitic arthropods and mammals. 1985, John Wiley & Sons, New York, pp 505-68
Taxonomy
Cupp EW: Biology of ticks. Vet Clin North Am Small Anim Pract. 1991, 21, 1-26
Pfister K: [Arthropodes in Ruminants.] In: Schnieder T (ed.): Veterinärmedizinische Parasitologie. 6th edn., 2006, Parey in MVS, Stuttgart, pp 235-292 [in German]
Sonenshine DE: Biology of Ticks. Part 1, 1991, Oxford University Press, New York
Hard Ticks
Kimmig P, Hassler D, Braun R: [Ticks – small bite with nasty consequences.] 2000, Ehrenwirth, Munich [in German]
Mehlhorn H: Encyclopedic Reference of Parasitology. 2nd edn., 2001, Springer Verlag, Berlin
Sonenshine DE: Biology of Ticks. Part 1, 1991, Oxford University Press, New York
Further Reading
Bowman DD: Georgis’ Parasitology for Veterinarians. 9th edn., 2009 , Saunders/Elsevier, St. Louis
ESCCAP guideline – Control of Ectoparasites in Dogs and Cats
Sonenshine DE: Biology of Ticks. Part 1, 1991, Oxford University Press, New York
