Toxicity occurs when a female tick injects a neurotoxin through her saliva into the host. The toxin prevents the signal from nerves from reaching muscles, resulting in flaccid paresis (hindlimb weakness) and eventual paralysis.
Clinical signs are seen 5-9 days after tick attachment, and progress from paresis to quadriplegia within 24-72 hours. Death may occur from respiratory failure (paralysis of respiratory muscles) in 1-5 days if ticks are not removed. With North American tick paralysis, removal of all ticks results in quick improvement within 24 hours and complete recovery within 72 hours.
Early clinical signs may include alteration of voice (laryngeal paralysis) followed by acute hindlimb weakness, incoordination, change in breathing rate, coughing, gagging, or vomiting. As the paralysis progresses, all four legs may be involved. The animal becomes unable to sit, stand, or lift its head. Respiration may initially increase and then becomes slower and labored. Regurgitation, saliva pooling, and gagging may be seen due to esophageal paralysis. Body temperature may be normal initially followed by hypothermia or hyperthermia.
No specific tests are available to diagnose canine tick paralysis. It is diagnosed based on acute sudden onset of progressive hind limb paresis and paralysis in a tick-infested area. The offending tick may not be present by the time clinical signs begin. Blood and chemistry values are usually within the normal range.
Signs of improvement are seen within 24 hours following removal of ticks. The presence of additional ticks or other causes of paralysis must be considered if the animal does not recover following tick removal. The prognosis in most cases is good.
Affected animals should be kept in quiet and relatively dark environments, with comfortable bedding provided. Recumbent animals should have their heads elevated to prevent aspiration and excessive saliva should be removed.
Animals usually require hospitalization for 24-48 hours.
Food and water is withheld until paralysis has resolved. Supportive intravenous fluids may be indicated. Tick antiserum, when administered early, can be useful although this is not widely avaialable. Attached ticks must be removed carefully. A pesticide (acaricide) may be applied to kill all the attached ticks. In advanced cases, oxygen, mechanical or manual ventilatory support may be necessary. Body temperature should be monitored and corrected as required.
Visible improvement should be noticed within 24 hours following tick removal. Death occurs in less than 5% of patients. Elderly dogs with pre-existing heart or lung conditions may be at higher risk.
Kline KL. Tick Paralysis. In: Cote Etienne, ed. Clinical Veterinary Adviser: Dogs and cats. Saint Louis: Mosby Elsevier, 2007;1085-1086.
Tick Paralysis. In: Kahn CM, ed. The Merck Veterinary Manual, 9th Edition. New Jersey: Merck and CO., Inc, 2005, 1073-1076. .
Safdar A. Khan, DVM, MS, PhD
Sharon Gwaltney-Brant, DVM, PhD, DABVT, DABT