Paralysis ticks are found in a variety of habitats but are especially common in wet sclerophyll forests and temperate rainforests. They have very few predators, and are more likely to succumb to desiccation from high temperatures and low humidity. From the enormous numbers of eggs (2,500-3,000) deposited in the moist leaf litter by the female before she dies, only a fraction will survive and eventually grow to become adults. The six-legged larvae hatch after the eggs have incubated for 40-60 days. To moult to the next stage, the larval tick must obtain a blood meal.
In searching for a host, they display a behaviour referred to as ‘questing’, whereby the tick climbs up into the nearest vegetation and waves its forelegs to and fro slowly, hopefully contacting a prospective passing host. This is usually a native animal such as a bandicoot, which is the main host, but also possums, kangaroos and humans. This questing behaviour is undertaken each time a host is required for blood. Ticks usually do not climb higher than around 50cm in the vegetation and there is no evidence to suggest that they fall out of trees.
Once a suitable host is found, the larvae will blood feed for 4-6 days, drop from the host and moult to the eight-legged nymphal stage. Nymphs require a further blood meal for 4-8 days before moulting to the adult stage. Both female and male ticks quest for a host, but for different reasons: the female for a blood meal, the males to search the host for female ticks in order to mate and sometimes feed from them. Males may actually parasitise the female ticks by piercing their cuticle with their mouthparts to feed on her haemolymph (the tick’s blood) and up to 3-4 males have been found feeding on one female tick. Male ticks rarely bloodfeed on a host. The adult female Paralysis tick will feed for up to around 10 days, drop off the host and lay eggs over several weeks.
The entire life cycle of the Paralysis tick, involving 4 stages and 3 hosts, will take around a year to complete. Each life stage can be present throughout the year, although for the Paralysis tick, adults are more abundant in the spring and the early summer months, larvae in mid to late-summer, and nymphs during winter. Tick paralysis is most likely to be seen in children. The initial symptoms of tick paralysis may include unsteady gait, increased weakness of the limbs, multiple rashes, headache, fever, flu like symptoms, tenderness of lymph nodes, and partial facial paralysis.
Tick paralysis develops slowly as the tick engorges, which will take several days. Despite the removal of the tick, the patient’s condition typically will continue to deteriorate for a time and recovery is often slow. Undetected ticks are another possible reason for any prologed debilitation and should always remain a concern. Improvements in modern medicine and the development of a tick antitoxin have prevented further deaths from tick paralysis in the last 70 years. The antitoxin is available from the Commonwealth Serum Laboratories. Despite these developments, a few cases of tick paralysis in children are seen at major hospitals each year. Additionally, ticks take a high toll on pets every summer.
If a tick is detected and remains attached to the skin, never attempt to place any chemical such as methylated spirits onto the tick, nor should it be touched or disturbed, as the tick will inject saliva into the skin, which could make the situation worse. Rather the tick should be sprayed with an aerosol insect repellent preferably containing pyrethrin or a pyrethroid. The combination of hydrocarbons and the pyrethrin acts as a narcotic and a toxicant, and prevents the tick from injecting its saliva. The tick should be sprayed again one minute later and left. After 24 hours it should drop off naturally or be gently removed with fine-tipped forceps. It is normal for a tick bite to remain slightly itchy for several weeks, however if other symptoms develop, then a doctor should be consulted immediately.
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