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

Soft ticks (Argasidae)

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Characters of Soft-ticks

The description soft derives from these ticks lacking hard, sclerotized, plates on their integument. However, these ticks have tough leathery integuments and can survive long periods of harsh conditions without feeding. The body profile is rounded when seen dorsally, and unfed ticks have a thin, flattened, appearance when seen laterally. Engorged ticks become fat and rounded.

Photograph shows dorsal surface of an adult Ornithodoros Soft-tick, with its highly textured surface and legs with humps.

Mouthparts are ventral, and small relative to size of body. There is little sign of any segmentation of the body of soft ticks; the gnathosoma bearing the mouthparts is inconspicuous and ventral. Soft-ticks never have antennae. The sexes differ externally by shape of the genital aperture (wide in females, narrow in males).

Soft-ticks mostly feed rapidly as temporary parasites without any attachment to their hosts. Their life-cycle is an incomplete metamorphosis (see Acarines general) However: larvae of Argas species attach to host for about one week; larvae of Ornithodoros species do not feed; adult Otobius do not feed. Soft-ticks mostly reside within the nest or resting site of their hosts; their behavior is nidicolous .

Diagram of feeding at skin represents a Soft-tick feeding by use of its piercing chelicerae to reach down to dermal capillaries. These ticks do not attach firmly to their hosts in the way that Hard-ticks do.

Glossary

• Disc = Flat, smooth, circular or oblong, raised areas on surface of integument (3 on Argas).
• Hump = An irregular profile of legs of some Soft-ticks (6 on Ornithodoros).
• Lateral suture = A distinct marginal line between dorsal and ventral surfaces of some Soft-ticks (2 on Argas).
• Mammillae = Small rounded protrusions forming a distinct pattern on integument of some Soft-ticks (2 on Ornithodoros, also photograph).
• Pulvilli = Adhesive organs on legs of some acarines but not on Soft-ticks.
• Reticulated = A pattern of a fine network on surface of some Soft-ticks (2 on Ornithodoros).
• Scutum = A sclerotized plate on dorsal surface of some acarines but not on Soft-ticks.
• Spiracle = Opening of respiratory system; Soft-ticks have one each side of main body, above area between leg pairs 3 and 4 (8 on Argas).
• Spine = A thick sharp extension of the integument of some acarines and insects (3 on Otobius).

Argas (Argasidae)

Characters: adult, lateral. 1- Body profile is a regular oval viewed dorsally; body length of adult is approx 6mm. 2- Dorsal and ventral surfaces of body meet to form a distinct lateral margin or suture. 3- Integument has rough texture of fine irregular ridges and discs; setae are sparse and short; body is yellow/brown. 4- A scutum (or dorsal plate) is never present. 5- Eyes are absent. 6- Legs are long and slender; they end in a pair of claws but pulvilli are absent; setae are sparse and short. 7- Mouthparts are small and ventral (may project anteriorly in larva of some species). 8- Spiracle is small and situated above legs 3 to 4.

Hosts: Poultry and other birds are the hosts to which these ticks are adapted. Argas ticks are known as Fowl-ticks, Poultry-ticks, or Tampans. Argas persicus and similar species are widespread pests of poultry houses, living in the structure of the bird's housing and crawling at night onto the birds to take short blood meals. This is nidicolous behavior.

Signs and disease: Feeding by these ticks causes emaciation, weakness and reduction in egg laying. Inflammation and small granulomas in skin at feeding sites develop. Signs of paralysis may occur. Large infestations of poultry houses lead to severe loss of production or death of birds. Argas species transmit the bacterium Borrelia anserina causing Avian spirochetosis .

Ornithodoros (Argasidae)

Characters: adult, lateral. 1- Body profile is an irregular oval viewed dorsally; body length of adult is approx 8mm. 2- Integument has rough texture of small rounded raised areas (mammillae) and areas with fine reticulated patterns. Setae are widespread and medium length; body is grey/brown. 3- A scutum (or dorsal plate) is never present. 4- Mouthparts are small and ventral. 5- Eyes may be present (situated laterally as one or more pairs), or eyes are absent. 6- Legs are long and their segments often bear distinct humps; legs end in a pair of claws; pulvilli are absent. 7- Spiracle is small and situated above legs 3 to 4.

Hosts: Pigs, camels, cattle, horses, donkeys and many other mammals including humans, may be fed on by these ticks. Also poultry birds may be used as hosts by immature stages of some species.

Signs: Irritation, biting-stress and signs of paralysis may occur.

Disease: The short (30 minute) feeding time of adult Ornithodoros is painful: tethered or housed animals may suffer severe stress, leading to loss of production. Ornithodoros savignyi causes a form of toxemia when it feeds. This is not due to a toxin that is functional for the tick, in contrast to spider or scorpion venom, but the paralytic effects can sometimes be fatal. Species in the O. moubata complex transmit African swine fever virus between pigs, and from warthogs to pigs. They are also notorious in Africa for transmission of Borrelia duttoni bacteria causing Human relapsing fever to people living in mud-built houses .

Otobius (Argasidae)

Characters: second nymph, lateral. 1- Body profile from dorsal view varies depending on feeding and stage of development, typically it shows a widely bulging anterior part and a narrower posterior part. 2- A scutum (or dorsal plate) is never present; eyes are absent. 3- Integument is covered in thick sharp setae in the form of spines; body is grey/brown. 4- Mouthparts are small and ventral. 5- No genital aperture is present (none occur in larvae or nymphs of ticks). 6- Legs are stout, plain, and end in a pair of claws.

Hosts: Cattle, sheep and goats, horses, alpacas, dogs, and other mammals including humans are infested by the Spinose ear-tick, Otobius megnini. Infestations of humans are usually associated with close contact with infected horses or other domestic animals. Ticks of this small genus have an unusual life-cycle. Larvae crawl from the soil or walls of animal housing onto hosts and then to their outer ear canal to feed. Larvae molt there and feed and molt through two nymph stages in the ear. Engorged nymphs detach, molt and the females lay eggs without further feeding.

Signs and disease: These include irritation, head-shaking, anorexia, and ear canker. Biting-stress is severe and causes loss of condition. Damage to ear canal and drum may permit invasion by Screw-worms, or bacterial infection, with potentially fatal consequences .

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