An American Dog Tick, or Dermacentor variabilis. Photo by CDC.
What is Tick Paralysis?
Tick paralysis (also known as tick bite paralysis, or tick toxicosis) is caused by neurotoxins secreted in saliva by certain species of female ticks. Neurotoxins are chemicals that damage nerve cells and can cause a wide array of symptoms, including paralysis (the loss of mobility and movement), due to nerve toxins in tick saliva. There are differences in ticks all over the world, and the health impacts they may have. In this article, we concentrate on tick paralysis information for species found in North America, Europe, and Australia.
Regional and Tick Species Differences
In North America, Dermacentor and Ixodes spp. are primarily involved. Tick paralysis exclusively affects dogs in North America. The disease has not been reported in domestic cats. In Australia, Ixodes holocyclus, Ixodes cornuatus, and Ixodex hirsti are primarily involved in dog and cat cases. Female adults of I. holocyclus are mainly responsible for tick paralysis in the eastern coastal region of Australia, although larvae or nymphs can trigger neurotoxicosis if they are present in large numbers. I. cornuatus is responsible for the disease mainly in south-eastern Australia and Tasmania.
In Europe, Rhipicephalus sanguineus is responsible for most canine cases. Feline cases have not been reported in Europe.
Clinical Signs of Tick Paralysis in North America
Not all ticks produce the toxin and not all tick-infested animals develop paralysis.
Signs usually occur five to nine days after tick attachment, and include:
- Rapidly ascending, lower motor (movement) weakness. (The motor nerve problems start with the rear limbs and move forward to involve the front limbs.)
- Signs tend to start with weakness in the hind limbs, followed by weakness in the front limbs and paralysis of all four legs.
- Occasionally, nerves of the head may be affected, resulting in facial weakness, voice changes, swallowing problems, or decreased muscle tone in the jaw.
- In severely affected patients, the respiratory muscles may become paralyzed. Signs tend to be symmetrical ( equal on both sides of the body).
- Pain sensation remains intact.
Clinical Signs of Tick Paralysis In Europe
Signs of tick paralysis are similar to that of North American cases, and animals have symmetrical signs.
Clinical Signs of Tick Paralysis In Australia
Because the species of ticks are different, in Australia the neurologic signs observed in pets are more severe and rapidly progressive in affected animals. Both dogs and cats can be affected, and paralysis of all legs can develop within hours.
Other signs include:
- Drooling, megaesophagus (where the esophagus or food tube from the mouth to the stomach becomes enlarged and loses the ability to move food), and regurgitation.
- Animals’ pupils are often dilated and poorly responsive to light.
- The urinary bladder may be distended, causing urination problems.
- Rapid, abnormal heart rates and high blood pressure are possible.
- Fluid collection in the lungs and breathing issues can also occur, which leads to not getting enough oxygen.
- Neurological problems affecting specific areas – typically on one side of the body rather than both (i.e., asymmetrical) – are found consistently in a proportion of dogs and cats with tick paralysis from I. holocylcus.
In one study, asymmetrical signs were observed in 8% of dogs with I. holocyclus tick paralysis. In the asymmetrical cases, tick(s) were present on the same side as the neurologic problems. Paralysis of the respiratory muscles is more common than in North America and death can occur within one to two days if treatment is ineffective or inadequate.
Diagnosis is based on clinical signs, finding a tick on the body of the patient, and rapid resolution of clinical signs after removal of the tick. (Either manual removal or treatment with a quick-kill, anti-tick product.)
Diseases that can be confused with tick paralysis and that will need to be ruled out by your veterinarian are acute polyradiculoneuritis (a disease that causes paralysis and sometimes facial and vocal weakness), botulism (another motor paralysis condition caused by eating the toxic bacteria Clostridium botulinum), and myasthenia gravis (a crisis form of this disease, which means rapid onset of full body weakness, respiratory failure, and megaesophagus).
Ticks can range in size, and it is important to check the whole body thoroughly.
When tick paralysis is suspected, your veterinarian will examine your pet thoroughly for ticks. This may include whole-body clipping for long-haired dogs. All areas of the body will be checked, and all ticks found will be removed. Removal is the primary means of treatment.
Your veterinarian may apply a medication to kill parasites (a parasiticide) on the skin/fur. However, it can take the parasiticide up to 48-72 hours to kill any remaining ticks present on your pet, and some may be younger, smaller, and difficult to see. Because it is sometimes difficult to remove all ticks in this situation, clinical signs may progress during this time.
For tick paralysis in North America and Europe, removal/death of tick(s) and supportive care are frequently all that is required, because clinical signs improve rapidly after the tick stops feeding. In Australia, tick removal may work if clinical signs have not yet developed. If signs have already started, more treatment of the signs and/or antiserum will be required to control the toxicosis.
Immunity to tick neurotoxins after being exposed in the past, or natural immunity. has been described in dogs that have survived tick paralysis; however, natural immunity doesn’t last long, and the animal can develop tick paralysis again after another tick bite.
In Australia, tick antiserum (TAS, tick antivenom, tick antitoxin) from hyperimmune dogs may help in the treatment of tick paralysis. Controlled clinical studies are lacking, but there is strong evidence from users of TAS that commercially available TAS is beneficial when dealing with the Australian toxin. However, administration of TAS carries the risk of drug reactions, so your veterinarian will weigh the positives and negatives of the use of this antiserum.
Supportive care is extremely important for paralyzed patients. Such care may include intravenous fluid therapy, physiotherapy, urinary bladder management, and hand feeding with the animal in a sternal (laying on the belly) or vertical position (sitting on the bottom, sometimes in a specialized chair) for dogs that have developed megaesophagus. In addition, a feeding tube may be considered. If there is lung damage, antibiotics may be necessary. If there are eye problems, eye lubricants may be needed.
Respiratory failure is a major complication of tick paralysis, especially from I. holocyclus, so oxygen supplementation and mechanical ventilation, where a tube is placed into the lungs and attached to a ventilation machine to assist with breathing, may be required.
In North America, the prognosis for tick paralysis due to Deramacenter variabilis or Deramacenter Andersonii is good, provided all ticks on the patient are removed or killed and adequate nursing care is provided. Removing the tick(s) results in an improvement in signs within hours. Complete recovery usually occurs within one to three days. Occasionally, muscle weakness may persist for weeks, but most patients fully recover from this disease when treated appropriately. Death can occur in untreated dogs from paralysis of the respiratory muscles.
In Australia, the prognosis for tick paralysis due to Ixodes holcylus is guarded and recovery may be prolonged. In Australia, tick removal may suffice if clinical signs have not yet developed. Otherwise, the clinical signs will progress if appropriate medical treatment is not done. Dogs less than six months of age and small breed dogs are at significantly higher risk of death. Dogs with low oxygen levels have a better chance of survival if they receive mechanical ventilation than if they do not. Occasional cases of sudden death have been reported within a few weeks of recovery. Therefore, your veterinarian will recommend that your pet have a non-stressful, 2-week resting period after recovery.
Preventing Tick Paralysis
The best way to prevent tick paralysis is to use tick control products. Check pets daily and remove any ticks. Always see your veterinarian right away if you notice any concerning signs after a tick bite.