Diseases of the Nervous System

Chapter 55 Diseases of the Nervous System


Nervous system diseases have a large impact on the equine industry. Neurologic diseases can progress from fairly minor (alteration in gait and performance) to very serious (inability to rise and death). Effects of nervous system diseases can be brought about by trauma to nerves, inflammation around nerves, or alterations in neurotransmitters. In most instances, there is no specific treatment for a nervous system disorder, and good nursing care is all that can be done. Fortunately, many neurologic diseases can be prevented by vaccination.



RABIES


Rabies is a zoonotic disease with the greatest public health implications. Most states have laws mandating the vaccination of dogs and cats, and some mandate the vaccination of horses; the vaccine is available only through licensed veterinarians. Even if not dictated by state laws, it is advisable to have yearly rabies vaccination given to horses. Any animal that is showing neurological signs, especially if there is a known history of having been bitten by another animal, should be suspected of having rabies.


The infectious agent is a Lyssavirus. An infected animal, usually a raccoon, skunk, fox, or bat, bites the victim and passes the virus in the saliva. The virus migrates through body and the nervous system and localizes in the central nervous system. The virus may affect the cerebrum, brainstem, or spinal cord.




CLINICAL SIGNS



• If the virus settles in the brain, extreme behavioral changes, often aggressive, are seen.

• If the brainstem is affected, behavior changes with the animal becoming more subdued and quiet are seen.

• If the spinal cord is affected, the animal exhibits ataxia that progresses to paralysis.

• Signs are rapidly progressive, and animal usually dies within 5 to 10 days of the onset of signs.


DIAGNOSIS



• Brain tissue examination


TREATMENT



• No treatment exists for rabies.



TECH ALERT


Wear gloves when examining any horse exhibiting neurologic signs.



INFORMATION FOR CLIENTS



• If an animal is bitten by a rabid animal and has been vaccinated, the animal should be revaccinated and observed for 45 days.

• If an unvaccinated animal is bitten by a suspected rabid animal, it should be euthanized. If the owner is unwilling to perform euthanasia, the animal needs to be watched closely for 6 months and HANDLED WITH EXTREME CAUTION.

• Euthanize any horse that has been exposed to rabies and shows neurologic disease.

• A yearly rabies vaccine will prevent the disease.


NARCOLEPSY


Narcolepsy is a disease characterized by inappropriate sleep activity, often taking the appearance of “fainting.” The condition is usually seen before 1 year of age. Owners report a history of the horse collapsing. The collapse may be initiated by stimulation of herd mates. Suffolk and Shetland ponies appear more likely to suffer from narcolepsy than other breeds. The disease is caused by a biochemical imbalance in the sleep–wake centers of the brain. Serotonin, dopamine, and norepinephrine all are involved in this condition.




CLINICAL SIGNS



• Signs can range from mild muscle weakness to full-blown sleep

• Horse’s knees may buckle, and the horse may become ataxic

• The frequency of episodes is variable, and the horse appears clinically normal between episodes


DIAGNOSIS



• A presumptive diagnosis is based on clinical signs and history

• Physostigmine can be used to elicit an attack

• Atropine can reverse signs in an attack


TREATMENT



• Treatment is usually unrewarding. Serotonin uptake inhibitors and antidepressants have been tried with limited success.


INFORMATION FOR CLIENTS



• These horses should be ridden carefully because they may suddenly fall, producing serious injury to the rider.


WOBBLER’S SYNDROME


Wobbler’s syndrome is a problem where the spinal cord is compressed by a narrowing of the vertebral canal, resulting in neurologic deficits. The condition is usually seen in young, fast-growing horses. Eighteen months of age appears to be a common age when owners notice onset of clinical signs. The condition is more common in Thoroughbreds and quarter horses than other breeds. Male horses appear to be more affected than female horses. The most common presenting complaints are a history of poor performance, weakness, and stumbling. Abnormal growth and/or articulation of the cervical vertebrae results in narrowing of the vertebral canal. The narrow vertebral canal causes pressure on the spinal cord. The condition may be congenital or a result of rapid growth or mineral imbalances, or both.




CLINICAL SIGNS



• Ataxia and weakness

• Stumbling, toe dragging

• Hind limbs usually more affected

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Aug 31, 2016 | Posted by in GENERAL | Comments Off on Diseases of the Nervous System

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