Sydney University Department of Medical Entomology Westmead Hospital
Ticks

The female Paralysis tick,
Ixodes holocyclus

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Introduction

Ticks are bloodsucking, external parasites that are often encountered by people during activities in the Australian bush. There are many species known to attack humans and so samples should be referred to our expert laboratory for proper identification. Over the last twelve years, the Department of Medical Entomology, ICPMR has been at the forefront of research into ticks and tick-borne disease, and has been the leading health authority for the provision of information on the ecology and control of this important public health pest.


Natural History

Female Paralysis tickThe distribution of our most medically important tick, the Paralysis tick, Ixodes holocyclus, is roughly confined to a 20-kilometre band that follows the eastern coastline of Australia. As this is where much of the human population resides in NSW, encounters with these parasites are relatively common. Although most cases of tick bite are uneventful, some can result in life threatening illnesses including paralysis, tick typhus and severe allergic reactions.

Ticks belong to the order Acarina, which also contains mites. The Australian tick fauna consists of approximately 75 species that can be divided into two families. The soft ticks (Family Argasidae) are represented by only a few species in Australia and are often associated with nests or resting places of animals. These ticks have a wrinkled appearance, which is akin to soft leather. The hard ticks, (Family Ixodidae), comprise the majority of our ticks and are distinguished by a hard dorsal plate in the shape of a fingernail and elongated mouthparts that have rows of backward pointing teeth. Some species of tick use these teeth in conjunction with a cement to remain attached to the host while blood feeding.

The Paralysis tick can be 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 of the eggs 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 to the top of 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 more than around 50cm in the vegetation and there is no evidence to suggest that they fall out of trees.

Various stages of the Paralysis tickOnce 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 bloodmeal, 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.


Clinical Presentation

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.

Tick typhus is an infection with a rickettsia (bacteria-like organism) transmitted from native animals by ixodid ticks and is confined to the eastern coast line of Australia and Bass Strait Islands. Clinical symptoms include headaches, multiple rashes, swollen glands, fever and flu like symptoms. The disease is rarely fatal and is commonly treated with antibiotics.

Lyme disease is a tick-borne infection common in the northern hemisphere and is caused by spirochaete bacteria. Symptoms are varied and may include rashes, fever, muscle and joint pain, and arthritis. The disease is not fatal and treatable with antibiotics. Despite clinical cases being reported from the early 1980's, there has been no confirmation that the disease occurs in Australia. (for more information go to the Fact Sheet on "Lyme Disease").

Allergic reactions are the most serious medical condition associated with ticks. These reactions can vary from a mild itching with localised swelling to widespread swelling with pain (click here to see one such reaction) to a severe and life threatening anaphylatic condition. Unlike with most other medical conditions associated with ticks, severe allergic reactions may occur with any tick stage. For people who develop severe allergic reactions, it is imperative that they must always avoid contact with ticks and avoid potential tick infested areas.


Laboratory Diagnosis

All stages of ticks are identified with the aid of a stereomicroscope and taxonomic keys, but many species are difficult to identify accurately. The Department of Medical Entomology provides a specialist identification service.


Treatment and Control

The best method of avoiding ticks is to stay away from known tick infested areas. If visiting such an area, light coloured clothing should be worn, as ticks will be much easier to detect. Trousers should be tucked into socks and shirts into pants. An insect repellent containing DEET or Picaridin should be applied, with a cream repellent applied to the skin and a spray repellent to footwear and clothing (note that DEET can damage some synthetic clothing). The repellent should be reapplied every few hours. All clothing should be removed on returning home and placed into a hot dryer for 20 minutes, which will kill any ticks that may still be on the clothing. Note that ticks can wander on the body for some two hours before attaching. This is how they become attached to the head (contrary to popular belief, they do not fall out of trees). The body should thereafter be searched well for ticks, especially behind the ears and on the back of the head. Children and pets should be examined for ticks after visiting bushland areas.

In locations where people live where they contact ticks in their backyard, then strategies can be undertaken to reduce the tick population and thereby minimise exposure. The Paralysis tick is very susceptible to dry conditions and so decreasing soil moisture can lessen their impact. This can be achieve through the reduction of foliage cover, which increases sunlight penetration to the ground, reducing the shrub layer, reducing mulching and watering, and ensuring that the lawn is kept mown low. Bandicoots, the main host of the Paralysis tick, can be kept out of the backyard through the use of animal exclusion fencing. This needs to go below the ground surface by 0.5m so that the animals cannot dig underneath. If ticks continue to be a problem, then insecticide control is an option. Currently the only registered insecticide for the control of the Paralysis tick in NSW is Brigade. Only a licensed pest controller can apply this chemical.


Tick Removal

If a tick is detected that is attached, 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 (if a repellent cannot be found which contains a pyrethroid, then Lyclear, a scabies cream containing permethrin will work fine). 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 (or dabbed with the Lyclear) 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.


Confirmation and Enquiries

Identification of ticks, and other medically important insects, is performed through the Medical Entomology Department at ICPMR, Westmead Hospital. The Medical Entomology Department is the only NATA accredited laboratory in Australia for the identification of arthropods of medical importance.

See 'Contacts' for further information.

Revised & updated 7/Nov/2003

 

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