Dogs and cats commonly succumb to toxins found in the saliva of the Australian Paralysis Tick (Ixodes holocyclus). This is a problem right along the east coast from Cairns in Queensland to Lakes Entrance near the Victorian border. A similar tick species causes paralysis in Tasmania. Left untreated, the outcome is often, if not usually, fatal. Whilst children are also at risk of paralysis, the most common human complaint is of local discomfort and allergic reactions.
Australian Spotted Fever (Tick Typhus, Queensland Tick Typhus) is an infection caused by the bacterium Rickettsia australis that is occasionally contracted by people exposed to tickbites- including the bites of larvae and nymphs. In addition, an Australian form of borreliosis (a bacterial infection similar to Lyme disease in Europe and the USA) is also suspected of being transmitted by ticks, although the organism has not yet been isolated.
It seems that Ixodes holocyclus can attach to many kinds animals, both native and introduced, 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 (shed their skin) and develop into the final adult stage of their life cycle (it is the adult stage that also produces the most toxins during feeding). Sporadic cases of tick paralysis, however, occur even in mid-winter.
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.
Of the adult stages, it is only the female which embeds itself into the skin of the host. The male wanders over the skin looking for its mate. The female prefers to mate before attaching. Once attached the female draws blood and gradually swells. Initially the engorgement is slow but after four or more days the engorgement becomes very rapid. The rapid engorgment phase is also associated with the greatest injection of the toxic saliva.
The dog or cat may show a great variety of signs that may be very subtle in the early stages. Early signs include: lethargy, inappetance, groaning when lifted, altered voice/bark, noisy panting, coughing, drooling saliva, gagging, minor vomiting and large pupils. Occasionally a single limb may appear to be weak or lame.
As toxicity progresses the signs become more characteristic: weakness and staggering (seen first in the hind legs) appearing "drunken", and a slower grunting respiration. Some animals are easily panicked at this stage and should be handled calmly. Ultimately there is complete inability to stand or even lift the head and the breathing is extremely laboured. A state of coma indicates that death is imminent.
When a tick is removed, the signs can continue to worsen for up to 48 hours, though worsening is usually most pronounced in the first 12-24 hours after removal.
TAGS recommends grasping the tick under its body with fine tweezers as close to the skin as possible, and withdrawing with a single continuous pull. Because paralysis ticks have long jaws and a barbed feeding tube, this may require considerable force. Various commercial tick removers and other kinds of medical forceps are also useful. Using a loop of cotton applied as a noose under the body of the tick may work too if there is not too much skin swelling around the tick.
Although the importance of not squeezing the tick's body is not established it is probably a good idea to try not to do so. Similarly it may be a good idea to avoid excessive manipulation of the skin at the attachment site. Some people also advocate wearing gloves when handling ticks.
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.
Whilst pre-killing the tick with an insecticide may facilitate removal, it may also cause a delay that allows the tick to inject more toxins. In humans, in whom allergy and infectious disease are more of a threat, the delay may also allow the tick to inject more allergens and infectious organisms. Some tick-killing chemicals may actually cause the tick to increase its injection of such allergens and infectious organisms.
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.
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 (usually involving hospitalisation) offers the best chance of full recovery.