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> Print.Ixodes holocyclus is the species generally responsible for allergic reactions.
Larvae and nymphs, as well as adults are capable of causing very severe allergic reactions. Dramatic local redness (erythema) and fluid swelling (oedema) and itch (pruritus) may develop within 2-3 hours of attachment of even one larva (if a person has been sensitised by a previous bite).
Frequently, a tick embedded over an eyelid will result in gross facial and neck swelling within three hours. The person can go on to develop very severe signs of tracheopharyngeal compression within 5-6 hours after the first onset of symptoms (Jones,1991). Sometimes there is blistering.
Attachment of a few larvae to a non-sensitised host provokes little or no response, even though the contact is prolonged over several days. However, towards the end of feeding some pruritus, erythema and localised oedema may develop at the site of attachment. Repeated infestation with the larva, as occurs in rural and wooded suburban areas where bandicoots are common, rapidly leads to the development of hypersensitivity. Then attachment of the larvae leads to formation of intra-epidermal blebs and eventually vesicles. Finally these rupture and the larvae detach and are lost. In experimental work with the cattle tick Boophilus microplus, this occurred within 6 hours. When, as is often the case, large numbers of larvae are involved, severe allergic dermatitis may result. The maddening rash that results is commonly referred to as scrub-itch. Outbreaks are seasonal in southeast Queensland and occur most commonly during January, February and March when larval populations are at their peak. Dermatitis is most commonly encountered in rural workers but may also result from gardening (Moorhouse, 1981). During damp summers any disturbance of taller plants - e.g. clearing lantana, can produce a shower of tick larvae.
Attachment of the nymphal and adult stages produce variable responses, many of which are clearly allergic in nature. Often, attachment may provoke little or no response and the patient may be quite unaware of the presence of a tick for some days (hypoaesthesia) and eventually minor itchiness may lead to its discovery. Conversely there is sometimes a locally heightened sensitivity or pain (hyperaesthesia) (Atwell and Fitzgerald, 1994). Such attachment sites are surrounded by erythema (redness) (Moorhouse, 1981).
After the tick is removed itchiness (pruritus) may recur at the site of attachment at intervals over some weeks, and a small firm lump usually forms within a day or so of the tick's removal. This again may persist for many weeks. There may be some discoloration of the area of the bite. In other cases the skin reactions may be severe with marked pruritus and considerable erythema, oedema and hardening (induration) (Moorhouse, 1981). People also report headaches (Atwell and Fitzgerald, 1994).
Whilst Haemaphysalis longicornis has also been implicated in "scrub itch", such reports are very rare and the species is unlikely to be responsible for many instances compared with Ixodes holocyclus.
The ornate kangaroo tick, Amblyomma triguttatum s. l., reportedly the tick most often biting humans in Western Australia, may cause a generally mild illness (Lee, 1975: Pearce and Grove, 1987; Russell and Doggett, 1995).
Argasid ticks such as Ornithodoros gurneyi (the kangaroo soft tick) found in many of the drier parts of Eastern Australia, readily bite humans, but such instances are uncommon because these areas are sparsely inhabited by humans. This tick has been associated with local reactions including inflammation, oedema, itching and susbsequent necrosis, and on occasions with severe systemic effects including giddiness, vomiting, temporary loss of vision and unconsciousness (Lee, 1975: Roberts, 1970; Russell and Doggett, 1995.
Allergic-type reactions in residents on Heron Island on the Great Barrier Reef have been attributed to Ornithodoros capensis (Humphery-Smith et al, 1991b; Russell and Doggett, 1995).
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If the tick can be found and removed before its engorgement has proceeded to any considerable extent, paralysis may be limited and transient. In some patients a purely local paralysis develops. A bite behind the ear for example can produce a palsy on that side of the face lasting for some days.
In young children (usually 1-5 years of age) the first signs of toxicity may include lethargy, loss of appetite and an unsteadiness in walking, with a tendency to incoordination (ataxia). The tick is usually found in the scalp, often behind the ear. A child may sleep for unusually long periods and be difficult to rouse. Often their voices change and they they may have difficulty in focusing. Muscular weakness soon develops and the child staggers and falls. Weakness increases until the child is unable to walk. The arms become tremulous on effort and obviously weak. There is difficulty in swallowing, and the muscles of respiration become affected, leading to dilation of the nostrils, laboured respiration, cyanosis and ultimately, death. If the patient survives this period of extensive paralysis, resolution then begins, leading eventually to recovery.
Respiratory support may be required for more than one week but full recovery occurs. This is slow with several weeks passing before the child can walk unaided. Anti-toxin has a role in the treatment of seriously ill children but there is a high incidence of acute allergy and serum sickness.
In older children and in adults, the first manifestation of toxicity may be difficulty in reading. Double vision (diplopia), aversion to light (photophobia), dilation of the pupils (mydriasis) and transient squinting may occur. Darting movements of the eyes (nystagmus) or a sluggish reaction to light may be detected. Adults usually suffer from dizziness, headache and a general weakness and lethargy.
"We probably see a couple [of children with tick paralysis] a year in the Emergency Department but would only need to ventilate every second year or so. We seem to have had increased numbers in SE Qld this [1999] Summer. We suspect tick paralysis in any child exhibiting unusual neurological signs because the presentation is so varied and often difficult to explain in conventional neurological terms. I have had children present with unilateral dilated pupil when the tick was between the shoulder blades. Cranial nerve palsy is the most common neurological sign. Progressive weakness starting in the legs can develop over 18 to 36 hours with clumsiness and slurred speech. Some children display bradycardia or other evidence of dysautonomia. All the severe cases with respiratory failure get 2 ampoules of antitoxin but there is seldom any immediate response. Recovery can take many weeks for these severely affected children. In population health terms, tick envenomation is a far greater medical problem for children than snake or spider bite (Dr Rob Pitt MBBS FRACP FACEM, Director Paediatric Emergency Medicine, Mater Children's Hospital in Brisbane , Dec 1999)."