Tick Paralysis

What is tick paralysis?
Tick paralysis is a severe, potentially fatal, complication due to the tick Ixodes holocyclus (Paralysis tick, Scrub tick, Shell-back) along the east coast of Australia. This is the most severe form of tick paralysis in the world.

What is the life cycle of the tick?
Although ticks are commonly thought of as insects, they are actually arachnids similar to scorpions, spiders and mites.

Ticks have four distinct life stages: Egg - Six-legged larva - Eight-legged nymph - Adult

Females deposit their eggs in protected habitats on the ground.

After the egg hatches, the tiny larva (“seed tick”) feeds on an appropriate host. The larva then develops (“moults”) into the larger nymph. The nymph feeds on a host and then moults into an even larger adult.

Host species Ixodes holocyclus can attach to a wide range of native and introduced hosts including birds and reptiles. The principal hosts, however, are the native marsupials and these usually have an immunity protecting them against the toxins. Even in these native animals, immunity appears to be gained by gradual and continuous exposure to ticks. Bandicoots and to a lesser extent possums are probably the most important hosts for Ixodes holocyclus in urban and semi-urban environments. Spring is the peak season for tick paralysis because this is when the ticks moult and develop into the adult stage (it is the adult stage that also produces the most toxins during feeding). Sporadic cases of tick paralysis, however, occur even in mid-winter.

How can my pet pick up ticks?
Ticks attach to passing animals that brush against long grasses and leafy vegetation onto which they have ascended. Some may fall from shrubs and trees or from birds flying overhead. They are sometimes brought into a house on sheets and clothing that has been hung outdoors.

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.

I. holocyclus is a deep feeder Feeding adult ticks will leave a red, raised thickening, or “crater” There is a concentration of saliva and presumably toxin in the granulomatous reaction around the tick mouth parts. It is thought that the residual toxin located in this granuloma is at least partially responsible for the increasing paralysis which occurs after the tick is removed.

Since paralysis of skeletal muscles is just one of the many effects a paralysis tick's toxin the term tick poisoning more accurately reflects the wide ranging signs of the toxicity syndrome. Poisoning by Paralysis Tick Most mammals such as calves, sheep, goats, foals, pigs, cats, cavies, rats, mice and man can be infested by the Australian Paralysis Tick. Fatalities resulting from a single engorged adult female tick are mostly reported in the young animals of the larger species and all ages and sizes of the pet species (dogs and cats). Larvae and nymphs can also produce toxic reactions in the host, with large numbers of either can induce paralysis in dogs and cats. Extent Localised to certain muscles in the vicinity of the tick. This is occasionally seen. Most noticeably, eyelid paralysis occurs in dogs with ticks on the face and may result in a loss of the blink reflex and consequent irritation leading to ocular discharge and even corneal ulceration. Some other examples- a tick on the face may cause displacement of the muzzle's midline. A tick near the anus may cause faecal incontinence or apparent diarrhoea. Generalised and involving the entire animal but often first noticeable as an incoordination and weakness of the hind limbs in dogs, cats etc. This is the more usual presentation of paralysis caused by the Australian paralysis tick. Severity Lethragy to complete atonic paralysis of all striated/skeletal muscle tissue (which in dogs includes a major portion of the oesophagus). Ixodes holocyclus also causes cardiotoxicity. Effects other than paralysis which may actually be more life threatening.

In most cases the time taken for an adult female to fully engorge while on the host varies from 6 to 21 days (with the earliest signs starting on the 4th day), the period being longest in cool weather. Thus a dog may carry a tick up to three weeks without the tick being significantly engorged or causing paralysis. It may even be possible to have a low grade form of intoxication for a week or so. In warm weather however the female engorges rapidly, which means she also injects her toxin more rapidly, thus causing onset of clinical signs in the typical 3-4 days (if the host is not immune). How is tick paralysis diagnosed? Diagnosis is usually straight forward, especially when a tick or its crater can be identified. However, the case gets harder when ticks are not evident (especially larvae/nymphs). In my experience up to 10 % of tick affected animals have no evident tick. I have seen animals presented with a wide range of problems including being hit by car, vomiting, breathing trouble with no paralysis, etc which have an underlying tick problem.

Some dogs may be presented for lethargy, inappetence, coughing, gagging, or grunting (as though in pain). Some dogs may be presented for regurgitation or vomiting, which may persist throughout the course of the disease. Similar signs are seen in cats with tick paralysis but affected animals are typically more distressed and agitated. Initially there is also often a change in voice, especially noticeable in Burmese and Siamese cats. This may be accompanied by retching. Pupillary dilation is prominent in cats but vomiting is rare in comparison to the dog. A rapid onset of signs appears to be associated with more severe disease and a higher likelihood of fatality. A single engorged adult female tick can kill the largest dog. Treatment for Paralysis Ticks If in doubt we will always opt to treat for a tick, since to delay can be disasterous! With current treatment regimes around 5% of tick victims die despite treatment. Applying pharmacological methods of reducing cardiac, pulmonary and oesophageal dysfunction is the focus of interest in treatment strategies.

How can ticks be prevented?
There are many different types of tick preventatives available in the marketplace. Some require less effort on the part of the owner than others. Some products are available over the counter, while others are only available through your veterinarian. There are effective monthly preventatives that are applied to the skin at the back of the neck and represent a convenient method of control for these ectoparasites. Your veterinarian will make specific recommendations to keep your pet parasite free.

What should I do if I find a tick on my pet?
Twist the tick anticlockwise.

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. 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. There is no distinct "head", only "paired jaws and a feeding tube" and these are attached to the tick's body via a short structure known as the basis capituli. The dangerous salivary toxins are located in the large visible body region of the tick, not the jaws. Therefore, even if the jaws were left behind in the skin this is not usually a problem in animals and certainly not as serious as potentially allowing further toxin to be injected from the tick's body region.

It has been claimed that more than 90% of ticks are found from the shoulders forward but they can be found anywhere - occasionally inside the mouth (even under the tongue!), nostril, ears, vulva and anus. Clipping may be useful in animals with a dense or matted coat. Searching the animal for ticks is done with minimal stress. We use acaricidal rinses to guard against ticks missed by searches.

Searching is best performed using two hands and running the fingers through the coat symmetrically, starting from the muzzle and working back over the head and ears, down around the neck , then chest and front legs. Pay attention to the lips folds, the face around the eyes and inside the earflaps If the animal has not yet shown signs of tick paralysis, removal of the tick may prevent development of the disease. However, if the animal is showing any signs then removal of the tick is not sufficient, because the disease is very likely to progress for up to 48 hours in the absence of specific therapy. Animals in anxious respiratory distress are best sedated before attempting tick removal. This is particularly the case with cats which can develop a state of frenzied gagging and struggling with handling. Animals must be kept in a comfortable, quiet, stress-free environment. This can mean the difference between life and death. Animals are often in respiratory distress and may have little compensatory reserve to cope with further oxygen demands brought about by anxiety. Food and water are initially withheld whilst the animal is paralysed because pharyngeal dysfunction, megaoesophagus, laryngeal paresis and a weak cough all predispose aspiration pneumonia. Tick antiserum acts to neutralise the toxin at the neuromuscular junction of skeletal muscle. Cardiac muscle receptors, however, are different. It is thought that cardiac toxicity is independent of skeletal muscle toxicity and moreover that tick antiserum does not protect against this cardiac toxicity Tick antisera is standardised to contain at least 500 CSIRO neutralising units per mL. It may be prudent to assume that most “mild” cases are being seen early rather than being mild and still give a standard 'full dose'. The initial additional cost of antiserum is countered by shorter hospitalisation and secondary support costs.

Daily searching and using tick-repelling or tick-killing sprays, rinses and collars are all useful in preventing paralysis in dogs. Currently fipronil (Frontline®) spray or permethrin (Permoxin®) rinse/spray are highly recommended for dogs. Tick collars are also effective for many dogs provided they do not get wet. Orally dosing a pet with pesticide (eg Proban® tablets) is also warranted in some situations. Unfortunately, there are no products licensed for use in preventing tick paralysis in cats but using either fipronil (Frontline®) or cythioate (Proban®) may help. Whilst pyrethrin rinses and shampoos will kill those ticks already on a cat they have little residual activity. Please note that one pyrethroid, permethrin, is highly toxic to cats. Your veterinarian can discuss the prevention options and recommendations that may suit your pet's situation. A vaccine against the tick toxin has been under development for some time but is not yet proven or commercially available.

Most important!
In domestic pets tick paralysis is just as life-threatening (though more slowly) as snake bite. If your pet shows any signs possibly indicating tick paralysis you are very strongly urged to contact your veterinarian for immediate advice. The effectiveness of anti-tick serum is most dependent on how early it is administered. Early treatment (involving hospitalisation) offers the best chance of full recovery. www.tickalert.org.au


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