Dogs get exposed to various types of toxic substances in the environment and through food. Some of them can have severe adverse effects on the nervous system.
Dogs frequently come in contact with organophosphates present in herbicides and pesticides that are widely used in the lawns and gardens. Many industrial chemicals also contain these toxic compounds that interfere with the metabolic activities of the body. Excessive exposure disrupts the functioning of acetylcholinesterase, an enzyme necessary for the working of the neurotransmitters that facilitate neuron to neuron and nerve to muscle communication. Mainly 3 types of toxicity are observed, namely, acute, intermediate, and delayed, and their effects vary too.
The first symptoms of acute organophosphate poisoning are increased salivation, vomiting, and diarrhea. These may be followed by twitching of the muscles, tremors, and extreme shortness of breath. The dog may have seizures and may eventually fall into a coma. In the intermediate form of the disorder, many of the above symptoms may be absent in the beginning, and the dog may just show a muscle weakness. However, within a few days, stiffness of neck as well as partial paralysis of all the limbs develops. Dilation of the pupils is typical.
Atropine, which can block the action of organophosphates, is used to treat both acute and intermediate toxicity. Various other drugs are used to treat the symptoms such as weakness of muscles and tremors. Long-term treatment over many weeks may be required.
Slow degeneration of the nerves is the effect of delayed toxicity. It does not involve the toxin’s action on acetylcholinesterase. The usual symptom is weakness in the hind limbs accompanied by lack of motor control that develops many weeks after the poisoning. This condition is not treated with any drugs.
Tick bites of different types of ticks can cause paralysis in dogs. Tick paralysis usually progresses rapidly, with certain species such as the Australian tick Ixodes holocyclus causing an especially severe form of paralysis. Partial paralysis in the hind limbs is the initial symptom, but it progresses to complete paralysis of all the limbs in just 2-3 days. While the dog does not have any sensory impairment or reduction in the level of consciousness, it may develop facial and respiratory paralysis. Weakness in the jaw muscles result in swallowing difficulties.
Prompt removal of the ticks, and the use of anti-parasitic ointments to destroy any remaining ones, will ensure a fast recovery in most cases of tick paralysis. But the paralytic reaction caused by Ixodes holocyclus of Australia has a high fatality rate from severe respiratory paralysis, even though a special serum is available to treat it.