By Norbert Fischer B.V.Sc.(Syd)
Tick lesions caused by I. holocyclus in domestic animals are usually firm swellings of the skin that vary in their size according to the stage of tick and the duration of attachment. The swelling usually has a central, slightly depressed 1-3 mm scab known as a tick crater. These lesions usually remain palpable for several weeks.
Tick lesions lesions rarely seem to cause irritation in domestic animals. Some animals may develop some discomfort when the live tick is touched or knocked. Sensitive dogs (e.g. Maltese terriers) may develop a painful lameness in a limb with an attached tick (this needs to be distinguished from a local paralysis).
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| ^ Silky Terrier which had its fur clipped to locate further ticks. The tick has been removed. The additional local loss of hair at the tick lesion gives an approximation of the size of the associated swollen area which forms a palpable nodule. |
In humans the lesion is initially hypo-sensitive but may later become hyper-sensitive (sometimes quite painful) and itchy and the lumps can remain as vague irritations for several months. It is not known whether this is due to retention of parts of the ticks mouthparts or fragments of the pedipalps or some other agent. If the hypostome (the central barbed feeding tube of the tick) is examined with a hand lens after removal of the embedded tick it is often found to be damaged.
When the tick carries the Rickettsia australis organism (causing Rickettsial Spotted Fever, also known as Queensland Tick Typhus) a characteristic eschar may form at the tick lesion (in 65% of cases) as well as a more generalised macular or maculopapular red rash. Changes in the regional lymph nodes draining the area of attachment can also lead to the formation of chronically sensitive enlargement within the node lasting for several years, particularly those around the head and neck.
For a description of how the tick inserts its mouthparts for feeding see Tick Feeding.
Domestic animals very rarely show allergic reactions to I. holocyclus tickbites but there is no reason for them not to occur.
Allergic reactions to ticks may be i) small local reactions, ii) large local reactions, iii) systemic reactions (anaphylaxis), and iv) unusual allergic reactions (Sonenshine, 1991).
Anaphylaxis, also known as allergic shock, has been reported in humans following contact with Ixodes ticks. The result is collapse and prostration. Apparently many people have experienced spectacular reactions when they have come into contact with both live and dead tick products. Having a tick simply walk over a person's hand produces in some people an intense discomfort and itching - what particular components of the tick body cause these reactions is unknown but it could be a water soluble component that is excreted through the cuticular canals (Jones,1991).
Larvae and nymphs, as well as adults are capable of causing very dramatic allergic reactions. Dramatic local redness (erythema) and fluid swelling (oedema) may develop within 2-3 hours of attachment of even one larva.
In southeast Queensland a "maddening rash" (known locally as "scrub itch") is caused by infestation by many tick larvae. This especially affects people clearing leafy bushland such as lantana scrub. Not infrequently a single tick embedded over an eyelid will result in gross facial and neck swelling within a few hour. The person can go on to develop very severe signs of throat (tracheopharyngeal) compression within 5-6 hours after the first onset of symptoms. See also Allergic & Toxic Reactions in Humans.