Parasitic Insects, Mites and Ticks: Genera of Medical and Veterinary Importance/Hard ticks

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Hard ticks (Ixodidae)[edit]

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Characters of Hard-ticks[edit]

These ticks are described as hard because of various hardened (sclerotized) plates on their body surface, especially the scutum (or dorsal plate). The scutum of some species contains colored pigment or enamel, making patterns known as ornamentation. The entire body is clearly divided into anterior gnathosoma bearing the mouthparts, and the posterior idiosoma bearing the scutum and legs. The profile of the idiosoma seen dorsally is a regular oval.

Amblyomma-variegatum-female-male-dorsal.jpg
Photograph shows female and male Hard-ticks of genus Amblyomma, most species of which have distinctive colored patterns on their dorsal surface, and pale bands on their legs. The piercing mouthparts are long and stout.
Hyalomma feeding skin.png
Diagram of skin represents a Hard-tick attached to its host by a salivary cement (stipple shaded). A feeding lesion is created within the host's dermis. Only the chelicerae and hypostome penetrate the skin; the palps remain superficial.

Legs are well developed. They end in a pair of claws and a pulvillus. Hard-ticks never have antennae. However, the first pair of legs have a sensory structure (Haller's organ) used in a way similar to insect's antennae. Mouthparts project anteriorly, clearly seen from dorsal or ventral views. The mouthparts (consisting of a pair of palps, cheliceral sheaths and hypostome) are borne on the basis capituli. When feeding the chelicerae and hypostome form the tube that pierces host's skin. Female ticks have a pair of porose areas on their basis capituli used for waterproofing eggs (appear similar to eyes). Eyes are present in some genera; always one pair on the anterior margins of the scutum. Females have a scutum on anterior dorsal surface of the idiosoma; males have a scutum (= conscutum) that covers entire idiosoma. Spiracles of Hard-ticks are borne on large plates in a position posterior to leg pair 4.

Hard ticks always feed only once at each of the larva, nymph and adult stages. The feeding takes several days as larvae, to one week or more as adults. The ticks attach firmly to their host's skin. The feeding sites of hard ticks usually create a sterile abscess where the ticks feed on lymph and then whole blood at the final stage of feeding. After the ticks detach the salivary glue that they leave behind is antigenic and stimulates inflammation and formation of granulomas.

Life cycles vary from one-host, two-host or three-host. Immature stages of Hard-ticks will attach and feed on a wide variety of hosts including humans (but no species maintain their population by feeding and reproducing on humans) [1] [2] [3] [4] [5] [6].

Rhipicephalus tick life-cycle.png
Diagram represents the life-cycle of a Hard-tick. This is an incomplete metamorphosis. There is single feed to repletion for each of the larva, nymph and adult stages, each on a separate host in a three-host feeding cycle. The non-feeding stages of two-host and three-host ticks are spent off the host, on ground or vegetation (below the horizontal bar) where they molt then wait for a host to approach. Species with a one-host feeding cycle have only the egg laying female, eggs and larvae off the host on the ground and vegetation.

Glossary[edit]

  • Anal groove = A shallow groove in the integument that is posterior or anterior to the anus (9 on Amblyomma, 7 on Ixodes).
  • Basis capituli = Posterior part of the gnathosoma, bearing the anterior mouthparts.
  • Conscutum = A sclerotized plate covering dorsal surface of male hard ticks (6 on male Amblyomma).
  • Coxa 1 spurs = First segment of legs of some Hard-ticks are formed into a spur (7 on Dermacentor).
  • Enamel = A pigment coloration of the integument, usually on scutum and conscutum and forming a pattern known as ornamentation (see photograph of Amblyomma)
  • Eyes = Some Hard-ticks have a pair of simple eyes on the edge of the scutum or conscutum (5 on Amblyomma).
  • Festoon = A bulge in the posterior outline of some hard ticks (6 on Hyalomma).
  • Gnathosoma = Anterior section of body of ticks, bears the mouthparts and palps.
  • Haller's organ = A sensory pit on forelegs of hard ticks (4 on Amblyomma).
  • Porose areas = Rounded areas of pores that secrete wax to waterproof eggs, on basis capituli of female hard ticks (resemble eyes).
  • Sclerotized plates = Area around anus of males of some hard ticks have characteristic plates (8 on Hyalomma).
  • Scutum = A sclerotized plate on dorsal surface of female hard ticks (6 on female Amblyomma).
  • Spiracle = Opening of respiratory system; on hard ticks a pair of large plates with pores posterior to coxae of hindlegs.
  • Ventral plaque = A sclerotized plate on posterior integument of some hard ticks (10 on Amblyomma).


Amblyomma (Ixodidae)[edit]

Amblyomma female dorsal.png

Characters: female dorsal. 1- Large robust ticks, body and mouthparts up to 7mm long. 2- Mouthparts are longer than, and equal in width to, the basis capituli; basis capituli has straight lateral margins. 3- Legs have patterns of a pale ring at ends of central segments. 4- Legs end in a pair of claws and a pulvillus; first pair of legs of females has a sensory Haller's organ (these three characters are found in all hard ticks). 5- Scutum bears prominent eyes (convex or flat). 6- Scutum and conscutum of most Amblyomma have colored enamel forming patterns characteristic of species. 7- Posterior body margin has a series of grooves forming a pattern of festoons (not clear in engorged females).

Amblyomma male dorsal ventral.png

Characters: male, dorsal left and ventral right. 5- Scutum bears prominent eyes (convex or flat). 6- Conscutum of many species have distinct colored enamel forming patterns characteristic of species. 7- Posterior body margin has a series of grooves forming a pattern of festoons. 8- Coxae 1 have a large outer spur and small inner spur in both sexes. 9- A distinct anal groove is posterior to the anus in both sexes. 10 Males have no sclerotized plates aligned with the anus, but in some species there are small ventral plaques aligned with the posterior body margin.

Hosts: Cattle, sheep, goats, and many other species of mammals, birds and some reptiles are infested. Humans may be infested with larvae they have encountered on pastures.

Signs and disease: These ticks cause irritation, inflammation, and formation of dermal granulomas at the feeding sites. Feeding sites of adults become painful and biting-stress can be serious in heavy infestations leading to distinct loss of gain in weight and production of milk. A favored feeding site of adult Amblyomma variegatum is on the cow's teats, impeding suckling. Value of hides is reduced by formation of scars at the dermal granulomas. Amblyomma variegatum and A. hebreum transmit the bacterium Ehrlichia ruminantium leading to Heartwater (Cowdriosis) in cattle, sheep and goats. Feeding of A. variegatum causes a systemic suppression of immunity in sheep and cattle; this may allow mild infection with Dermatophilus congolensis bacteria to become virulent, causing severe Dermatophilosis. [7].

Dermacentor (Ixodidae)[edit]

Dermacentor-female-dorsal.png

Characters: female dorsal. 1- Medium sized ticks, body and mouthparts approximately 4mm long. 2- Mouthparts are same length as the basis capituli; their width is as wide as or wider than the basis capituli; the basis capituli has straight lateral margins. 3- Scutum and conscutum of most species has a conspicuous pattern of white enamel on a dark brown background. 4- Legs are without pale rings. 5- Eyes are present (distinct in most species) 6- Posterior body margin has a series of grooves forming a pattern of festoons (not clear in engorged females).

Dermacentor-male-dorsal-ventral.png

Characters: male dorsal left, ventral right. 3- Conscutum of most species has a conspicuous pattern of white enamel on a dark brown background. 6- Posterior body margin has a series of grooves forming a pattern of festoons. 7- Coxae 1 have 2 large spurs (in both sexes). 8- Coxae of leg pair 4 are greatly enlarged. 9- Anal groove is distinct and posterior to the anus (in both sexes). 10- There are no sclerotized plates aligned with the anus.

Hosts: Cattle, sheep, goats, horses, dogs, wild ungulates and small mammals are used as hosts. Humans may be infested.

Signs, symptoms and disease: Irritation and biting stress is typical. Dermacentor andersoni feeding as adults on cattle can cause paralysis that may lead to death (this paralysis also can happen to humans). [8] [9]. Infestations of horses, deer and moose by Dermacentor albipictus may accumulate to massive levels causing severe stress or death. Dermacentor species transmit to cattle, horses and dogs several species of Anaplasma bacteria, and Babesia protozoa. Rickettsia rickettsii causing Rocky Mountain spotted fever (tick typhus) in humans is transmitted mainly by D. variabilis, the American dog-tick [10].

Distribution: Dermacentor species mostly inhabit temperate and cold regions, but the Tropical horse-tick, Dermacentor nitens of the Americas inhabits warmer regions.


Haemaphysalis (Ixodidae)[edit]

Haemaphysalis-female-dorsal.png

Characters: female dorsal. 1- Small ticks, body and mouthparts approximately 3mm long, body is yellow/brown. 2- Mouthparts are same length as basis capituli; second segment of palps is expanded laterally making mouthparts wider than basis capituli, and basis capituli has straight lateral margins. 3- Scutum and conscutum are plain, without colored patterns. 4- Eyes are absent. 5- Legs are without pale rings. 6- Posterior body margin has a series of grooves forming a pattern of festoons (not clear in engorged females).

Haemaphysalis-male-dorsal-ventral.png

Characters: male left dorsal, right ventral. 6- Posterior body margin has a series of grooves forming a pattern of festoons. 7- Coxae 1 have a single large spur in both sexes; coxae 2 to 4 have variable sized single spurs. 8- Males have no sclerotized plates aligned with anus. 9- Anal groove is posterior to the anus in both sexes.

Hosts: Several species of Haemaphysalis are common parasites of livestock: H. punctata (Red sheep tick) and H. sulcata on sheep; H. bancrofti on sheep; H. longicornis on cattle, sheep and horses. Dogs are commonly infested with H. leachi (Yellow dog tick), more so if they have free access to bush and scrub areas. Domestic cats are resistant to infestation with ticks (or effective self-groomers) but in tropical regions some H. leachi or H. spinulosa may be found on them.

Signs and disease: Irritation, inflammation at feeding sites, and pruritus are caused. Haemaphysalis longicornis, when heavily infesting cattle, will reduce weight gain and milk yield. Additionally, H. leachi transmits Babesia canis to dogs, and H. punctata transmits Babesia major to cattle and Theileria ovis to sheep [11] [12].


Hyalomma (Ixodidae)[edit]

Hyalomma-female-dorsal.png

Characters: female dorsal. 1- Medium to large ticks, body and mouthparts up to 6mm long, colored dark brown. 2- Mouthparts are longer than, but same width as, the basis capituli. 3- Scutum and conscutum are plain, without colored patterns (except in a few species) and with distinct ridges and depressions, together with many punctations. 4- Legs have pale rings (except in one or more species which have white enamel on their legs). 5- Eyes are present and distinctly convex. 6- Posterior body margin has a series of grooves forming a pattern of festoons.

Hyalomma-male-dorsal-ventral.png

Characters: male left dorsal, right ventral. 5- Eyes are present and distinctly convex. 6- Posterior body margin has a series of grooves forming a pattern of festoons. 7- Coxae 1 have a pair of large spurs in both sexes. 8- Males have large sclerotized plates aligned with anus. 9- Anal groove is posterior to the anus in both sexes.

Hosts: Cattle, camels, sheep, goats, and a wide variety of wild mammals are used as hosts. Favored feeding sites vary greatly but often are sites difficult for the host to groom such as groin, peri-anal region, or between claws of host's feet. Hyalomma aegyptium infests tortoises.

Signs and disease: These ticks cause variously: irritation, pruritus, pain, biting stress, inflammation, formation abscesses and dermal granulomas, and toxicosis. Hyalomma truncatum attached at interdigital clefts on host's feet cause lameness; the same species clustering on dogs cause skin necrosis. Engorging females of Hyalomma rufipes often cause a salivary toxemia in their hosts: as paralysis in camels, and as a depilating moist eczema called Sweating sickness in cattle. Hyalomma anatolicum transmits Theileria annulata protozoa between cattle, leading to Tropical theileriosis. These noxious blood-suckers are also serious threats to health of humans, to whom immature stages of H. marginatum transmit the virus causing Congo Crimea hemorrhagic fever [13] [14].

Distribution: Hyalomma ticks occur in dry and seasonally hot areas of Africa, Middle East, and Asia.


Ixodes (Ixodidae)[edit]

Ixodes-female-dorsal-ventral.png

Characters: female left dorsal, right ventral. 1- Females are medium size ticks, body and mouthparts approximately 4mm long; colored red/brown and black. 2- Mouthparts of females are longer than the basis capituli; second segment of the palps bends away from the piercing mouthparts, forming a gap. 3- Legs have no pale rings. 4- Scutum and conscutum are plain, without colored patterns. 5- Eyes are absent. 6- Coxae 1 have a single large spur. 7- Anal groove runs anterior to the anus. 8- Posterior body margin has no festoons.

Ixodes-male-dorsal-ventral.png

Characters: male left dorsal, right ventral. 6- Coxae 1 have a single large spur. 9- Males have large sclerotized plates covering much of their ventral surface; anal groove running anterior to the anus is defined by some of these plates. 10- Males are smaller than females of same species; they are colored brown/black. 11- Mouthparts of males are smaller than those of females.

Hosts: Cattle, sheep, goats and dogs are the principal species of domestic animal infested by species such as Ixodes ricinus. Deer also support all stages of ticks of this genus and are often the maintenance host in an area. Many Ixodes species will feed on a wide variety of mammals and birds, and humans are readily infested by larvae and nymphs.

Signs and disease: Irritation, inflammation, and pruritus are caused. Paralysis of hosts is caused specifically by feeding adults of I. rubicundus in the Republic of South Africa and I. holocyclus in Australia (these paralyses are associated with the ticks feeding on hosts of exotic species that are not the indigenous host species the ticks have evolved with). Ixodes species transmit Babesia divergens to cattle; Anaplasma phagocytophilum and Louping ill virus to sheep. Several species of Ixodes are notorious in human health as vectors of the Borrelia bacteria causing Lyme disease, and of the virus of Tick-borne encephalitis [15].


Margaropus (Ixodidae)[edit]

Margaropus-female-dorsal.png

Characters: female dorsal. 1- Small ticks; body and mouthparts approximately 3mm long; colored brown. 2- Mouthparts are shorter than but same width as the basis capituli. 3- Legs are long and stout; they end in a distinct spur as well as a pair of claws and a pulvillus. 4- Eyes are distinct in females (indistinct in males). 5- Scutum is plain (both sexes), without colored patterns. 6- Posterior body margin has no festoons.

Margaropus-male-dorsal.png

Characters: male, dorsal posterior. 3- Legs are long and stout; they end in a distinct spur as well as a pair of claws and a pulvillus (males of M. winthemi have legs 3 and 4 with bulging segments). 6- Posterior body margin has no festoons but a terminal bulge (caudal appendage) is present. 7- Ventrally, a pair of sclerotized plates is aligned with anus, and anal groove is indistinct.

Hosts and disease: Cattle and horses are infested on widely spread areas of their bodies by M. winthemi (Beady legged tick). This tick species is active during winter and may accumulate on horses sufficient to cause loss of condition (this tick is also known as Winter horse tick) [16] [17].

Distribution: Margaropus winthemi occurs only in Republic of South Africa; M. wileyi and M. reidi are found on giraffes in Kenya and Sudan respectively. These three species comprise the entire genus.


Rhipicephalus (Ixodidae)[edit]

Note on ticks in the sub-genus Boophilus (Blue-ticks, Cattle-ticks). Six species (boophilid ticks) within the genus Rhipicephalus have adapted to parasitism so well that they have a one-host feeding cycle, become small and have reduced distinctiveness of morphological characters. All the listed characters for Rhipicephalus apply to these boophilid species, so these ticks can easily be identified as members of this sub-genus. The Cattle-tick of the tropics and sub-tropics, widespread and important in large areas of the World, is a boophilid - Rhipicephalus (Boophilus) microplus, or simply Rhipicephalus microplus. The genus Boophilus has been placed within the genus Rhipicephalus because of affinities shown by its nucleic acids [18]. However, it remains convenient and correct to continue using the original genus name.

Rhipicephalus species dorsal.jpg
Rhipicephalus appendiculatus female and male upper row; Rhipicephalus microplus female and male lower row, to show differences in general appearance that may be found within a single genus (single photograph with identical scale throughout).
Rhipicephalus-female-dorsal.png

Characters: female dorsal. 1- Medium size ticks, body and mouthparts from 3mm to 6mm long; colored brown. 2- Mouthparts are same length as the basis capituli. 3- Basis capituli has extended lateral margins, making a hexagonal shape. 4- Scutum is plain, without colored patterns (except in two species); often there are distinct ridges and depressions, and varied punctations on the scutum (conscutum of male similar). 5- Legs have no pale rings. 6- Eyes are present and either convex or flat. 7- Posterior body margin has a series of grooves forming a pattern of festoons.

Rhipicephalus-male-dorsal-ventral.png

Characters: male left dorsal, right ventral. 6- Eyes are present, either convex or flat. 7- Posterior body margin has a series of grooves forming a pattern of festoons. 8- Coxae 1 have a pair of large spurs. 9- Males have a large sclerotized plates aligned with anus. 10- Anal groove is posterior to the anus in both sexes.

Hosts: Cattle, sheep, goats, horses, dogs, wild bovids, and many other species of mammal are typical hosts for these ticks. Cattle will often maintain all stages of Rhipicephalus appendiculatus (Brown ear-tick). Dogs similarly maintain all stages of R. sanguineus (Tropical dog tick). Most rhipicepalids have three-host life-cycles, but several such as R. evertsi (Red-legged tick) have a two-host life-cycle [19].

Signs: These ticks cause irritation, inflammation, pruritus, and biting-stress Also R. evertsi may cause toxemia in lambs.

Disease: Reduction in live weight gain of cattle occurs when large infestations of R. appendiculatus are on cattle [20]. The boophilid species transmit to cattle and sheep Babesia species of protozoa leading to Babesiosis, and Anaplasma species of bacteria leading to Anaplasmosis. Rhipicephalus appendiculatus transmits between cattle the protozoan Theileria parva leading to East coast fever; this tick also transmits between sheep the virus causing Nairobi sheep disease. Rhipicephalus sanguineus transmits between dogs the bacterium Ehrlichia canis leading to Canine ehrlichiosis [21].

Distribution: Rhipicephalus species are mainly confined to Africa. However, R. sanguineus has become distributed wherever domestic dogs inhabit warm regions; and in the sheltered habitat of human housing or dog kennels will flourish between latitudes 50 degrees north to 35 degrees south [22].

(to Table of Contents)


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References[edit]

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