An American Dog Tick, or Dermacentor variabilis. Photo by CDC.
Tick paralysis is caused by neurotoxins secreted in saliva by certain species of female ticks. In the U.S., Dermacentor and Ixodes spp. are primarily involved. In Australia, Ixodes holocyclus and Ixodes cornuatus are primarily involved. Two studies from Europe and Eygpt have incriminated Rhipicephalus sanguineus.
Clinical Signs of Tick Paralysis in the U.S.
In the U.S., signs usually occur five to nine days after tick attachment. Not all tick infested animals develop paralysis, and not all female ticks produce the toxin. Tick paralysis causes rapidly ascending, lower motor neuron weakness. (The motor nerve problems start with the rear limbs and move forward to involve the front limbs.) You may initially notice weakness in the hind limbs, followed by forelimb weakness and paralysis of all four legs. Occasionally, cranial nerves may be affected. Most commonly that results in facial weakness, voice changes, swallowing problems, or decreased muscle tone in the jaw. Pain sensation remains intact. In severely affected patients, the respiratory muscles may become paralyzed.
Clinical Signs of Tick Paralysis In Australia
Because the species of ticks are different, in Australia the neurologic signs 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 are drooling, megaesophagus, and regurgitation. The pet's pupils are often dilated and poorly responsive to light. Neurological problems affecting specific areas -typically on one side of the body rather than both - are found consistently in a proportion of dogs and cats with naturally occurring tick paralysis from I. holocylcus. Rapid, abnormal heart rates, hypertension, and pulmonary edema have been described. The affected animal may take fewer breaths, which results in less oxygen and other problems. Paralysis of the respiratory muscles is more common than in the U.S. and death can occur within one to two days if treatment is inadequate.
Neurological problems affecting specific areas - typically on one side of the body rather than both - are found consistently in a proportion of dogs and cats with naturally occurring tick paralysis from I. holocylcus.
Diseases that can be confused with tick paralysis and need to be ruled out by your veterinarian are acute polyradiculoneuritis, botulism, and myasthenia gravis (crisis form).
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.)
In the U.S., 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 improvement of 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, prognosis for tick paralysis due to Ixodes holcylus is guarded and recovery may be prolonged. Dogs less than six months of age and small breed dogs are at significantly higher risk of death. Dogs receiving mechanical ventilation because of hypoventilation have a higher survival probability than those with inadequate oxygenation.
Preventing Tick Paralysis
The best way to prevent tick paralysis is to use tick control products. Check pets daily and remove any ticks.