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Ticks act as carriers of various diseases in animals, including in dogs. Tick paralysis, or tick-bite paralysis, is caused by a potent toxin that is released through the saliva of certain species of female tick and which is injected into the blood of the dog as the tick infests the skin of the dog. The toxin directly affects the nervous system, leading to a group of nervous symptoms in the affected animal.
The toxins released by ticks cause lower motor neuron paralysis, which is defined as a loss of voluntary movement and which is caused by a disease of the nerves that connect the spinal cord and muscles. With lower motor neuron paralysis the muscles stay in an apparent state of relaxation.
An infestation of ticks is not necessary for a diseased state to occur. While multiple ticks are usually present on a dog that is showing symptoms of tick paralysis, tick-bite paralysis can take place after being bitten by only one tick. Conversely, not all animals, infested or not, will develop tick paralysis.
Symptoms usually begin to appear around 6-9 days after a tick has attached to the skin of the dog. This disease is somewhat seasonal and more prevalent in the summer time in certain areas of the U.S.. In areas where the seasonal temperatures are more consistently warm, such as in the southern states and northern Australia, ticks may be present throughout the year.
In the U.S., this disease is more commonly seen in dogs than in cats. In fact, cats in the U.S. appear to have a resistance to the tick toxin.
Symptoms and Types
There is history of a recent visit the dog has taken to a wooded area, or living in an area that is endemic to ticks. Symptoms are gradual in nature, including:
High blood pressure
Fast heart rate and rhythm (tachyarrhythmias)
Weakness, especially in the hind limbs
Partial loss of muscle movements (paresis)
Complete loss of muscle movement (paralysis), commonly seen in advanced disease state
Poor reflexes to complete loss of reflex
Low muscle tone (hypotonia)
Difficulty in eating
Disorder of voice (dysphonia)
Asphyxia due to respiratory muscle paralysis in severely affected animals
Excessive drooling (sialosis)
Megaesophagus (enlarged esophagus)
Excessive dilatation of pupil in the eye (mydriasis)
You will need to give a thorough history of your dog's health, onset of symptoms, and possible incidents that might have preceded this condition. For example, your veterinarian will ask about any recent visits you and your dog have made to wooded areas, especially within the last several days and weeks.
Your veterinarian will conduct a complete physical examination, looking closely at your dog's skin for the presence of ticks or for recent evidence of ticks. If ticks are found to be present on the skin, your veterinarian will remove the tick and send it to the laboratory for a determination of its species. Routine laboratory tests will include a complete blood count, biochemistry profile, and urinalysis. However, the results of these tests are often normal if no other concurrent disease is present along with tick paralysis.
In patients with respiratory muscle paralysis, blood gases will need to be calculated to determine the severity of the respiratory compromise. If respiratory muscle paralysis is occurring, low oxygen and high levels of carbon dioxide will be present in the blood, as the dog will not be able to properly inhale oxygen and exhale carbon dioxide. A chest radiograph may reveal an enlarged esophagus due to the extra effort of trying to breath.
The most important step in the diagnosis is to search for and find the tick that bit your dog so that it can be identified and its ability to transmit disease determined. Your veterinarian will thoroughly search all areas of your dog’s skin to find any ticks so that this can be done.