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 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.
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.
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.