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Ed: This assigment was written by Andrew Mc Allister, final year veterinary student, at the University of Queensland Veterinary School. Andrew's plans for next year are work in a mixed practice and he has his eyes on England at present.
Every year the paralysis tick, Ixodes holocyclus, will cause paralysis in over 100 000 companion animals on the east coast of Australia. Not only does it cause problems in our pets, but also the death of 10 000 calves and weaner cattle annually. This does not include the unknown numbers of newborn and adolescent alpacas, deer, sheep, goats, and horses that fall victim to this deadly arachnid. Therefore this tick can be a major problem for people who own livestock. Not only is the value of the animal lost when it dies, but the treatment is very expensive and prevention of tick paralysis is virtually impossible.
Ixodes holocyclus is restricted to the east coast of Australia, from northern Queensland to eastern Victoria, where the warm and humid conditions allow the survival of its natural hosts as well as its larval and nymphal stages during development. Bandicoots, brush-tailed possums, macropods, and koalas are the major natural hosts of the tick, but because they have developed natural immunity to the tick's toxins, they do not suffer paralysis.
The clinical signs that are seen in farm animals are the same as those seen in our pets. After the tick releases its toxins, a certain type of paralysis slowly moves from the limbs and tail up to the head, making the muscles relaxed and the joints easy to move. In veterinary science this is described as an ascending, flaccid paralysis. This paralysis is described firstly as coordination loss, which leads to paralysis of the legs and chest muscles. The animal's voice will also change from paralysis of the muscles in the 'voice-box'. Without treatment the animal eventually suffers from respiratory paralysis and death. They can also breathe stomach contents into their lungs, and these contents cause a severe and often fatal pneumonia. It's also been shown that the toxin released by Ixodes holocyclus causes sudden heart failure. Therefore, the prognosis for badly affected animals is not good. There is also a risk of this tick spreading tick-borne bacterial diseases like Rickettsia, which can cause severe flu-like symptoms in people.
Tick paralysis can be treated reasonably successfully now with a 95% success rate in companion animals. This is an enormous achievement, as it was only a few years ago that the recovery rate was 20%. However, because the treatments are expensive for large animals most livestock owners cannot afford to call the vet out.
Firstly the tick causing the paralysis needs to be found and removed as soon as possible. This can be done by carefully looking through the hair of an animal, clipping their hair off, or bathing them in a chemical solution to kill the ticks. Ticks do not release more toxins when they are removed, so they can be taken off the animal while they are still alive with tweezers, being careful to remove the tick's mouthparts as well. The reason for this is because if the mouthparts are left behind, they will cause a foreign body reaction similar to that caused by a splinter. However, the mouthparts will not release more toxins if they are left in the skin.
Ticks will also leave a red and a raised thickening, or 'crater', which can be found if the tick has already dropped off.
Treatments vary between vets, but the main drug used to treat tick paralysis is an injection of hyperimmune anti-serum into the jugular vein. This is a blood product collected from dogs that have been exposed to paralysis ticks over a long period. It contains antibodies against the toxins, so once it is given to an animal, any toxin that is still present will be removed and won't cause any more paralysis.
With livestock, the best results are seen in smaller animals such as calves and foals up to 70kg in weight. Treatment of such animals will often cost between $100-$300 for the antiserum alone.
Other drugs that can help the animal are atropine, a sedative or painkiller, a diuretic, an antihistamine and antibiotics to stop pneumonia.
Once an animal is treated for paralysis, recovery can occur from one day up to two weeks depending on how severely it was affected. During this time animals need to be kept on their sternum, because if they lay down on their side the likelihood of breathing stomach contents into their lungs increases dramatically. They can also be fed milk or water via a stomach tube to stop them becoming too dehydrated.
Prevention of tick paralysis is very difficult in livestock and pet animals. The Ixodes tick, the only species causing paralysis in Australia, feeds on three different hosts during its life cycle, which is why they are called a three-host tick.
This is in contrast to other ticks that parasitise large animals, like the cattle tick, Boophilus microplus, which spends its entire life on its host. The brown-dog tick, Rhipicephalus evertsi, is different again as it is a two-host tick.
Being a three-host tick create a control problem because dipping, spraying and using pour-ons with chemicals will not kill all of the paralysis ticks, as most of them will not be on the animal but will instead be living on their native hosts. Ticks that do feed on animals that have been treated with certain chemicals may also release some toxins before they take up enough blood and die.
Another problem with livestock is that it is usually not possible to check every animal for ticks every day like we do in our dogs and cats.
Some strategies to decrease the risk of animals being affected by tick paralysis are to remove vegetation where their natural hosts live and keep grass at a short length. There has been a lot of work done to try and develop a vaccine against the toxins, which would not only decrease paralysis cases in production animals, but also stop dogs and cats becoming paralysed as well. However at this time it is still in its developmental stages. Hobby farmers could try and use tick collars in their animals, but the manufacturer of these collars does not recommend this.
Tick paralysis is a big problem in all animals. The development of a vaccine against the toxins would herald the end of this disease, but it will probably be many years before this is available. Farmers can try different prevention techniques, but there is no way to fully stop paralysis occurring in large animals.
For more information on ticks and tick paralysis follow these links
The Danger of Paralysis Ticks