Understanding Neurological Horse Diseases

Neurological horse diseases can be devastating for horse owners and veterinarians alike. Equine protozoal myelitis, a neurological disease caused by a parasite, can be fatal if left untreated.

Horses are particularly susceptible to neurological diseases due to their unique anatomy and physiology. Their large brains and sensitive nervous systems make them more prone to damage from infections and parasites.

Equine protozoal myelitis is often transmitted through contaminated water or feed, making it essential to provide clean drinking water and avoid feeding horses spoiled or moldy hay.

For another approach, see: Equine Protozoal Myeloencephalitis Symptoms

Neurological horse diseases can be challenging to diagnose and treat, but understanding the causes can help you prevent or manage them. Many neurological problems in horses have similar symptoms, making them difficult to diagnose and treat.

Trauma is a common cause of neurological problems in horses. If a horse pulls back and falls on its neck on a hard surface, it can cause damage to the spinal cord or neck, leading to issues with the horse's body innervated beyond the original point of damage.

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Equine Protozoal Myeloencephalitis (EPM) is a parasitic infection that affects the central nervous system. It's typically caused by the protozoan Sarcocystis neurona and can result in ataxia, muscle wasting, and other neurological symptoms.

West Nile Virus (WNV) and other viral infections like Eastern, Western, and Venezuelan Encephalitis can cause inflammation in the brain, leading to symptoms like depression, fever, circling, head pressing, and paralysis.

Preventative measures can help reduce the risk of neurological conditions. These include safety measures when trailering, tying, or washing your horse, clean and non-moldy hay, parasite control, and yearly or biannual vaccination as recommended by your veterinarian.

Here are some common neurological diseases that can affect horses:

Clinical signs of neurological horse diseases can be quite subtle, making them challenging to diagnose.

Affected horses may exhibit general incoordination or stiffness when moving, leading to difficulties with walking up and down hills, tripping, or having trouble halting smoothly.

A long-strided stiff gait is often characteristic of the condition, but lower neck problems can manifest as weakness in the front limbs, resulting in a short-strided, choppy forelimb gait.

Signs of neck pain are inconsistent, but may include abnormal head and neck posture, decreased range of motion, or a rigid "weathervane" posture when moving.

Not every horse with a neurological disease shows overt signs of neck pain, and some may exhibit behavior changes under saddle, such as bucking, bolting, rearing, or stopping at fences.

Common signs of neurological problems in horses include ataxia, difficulty standing or walking, head pressing, muscle tremors or twitching, loss of balance or falling, circling or turning in circles, abnormal eye movements, and seizures.

Here are some key signs to look out for:

A veterinarian will typically perform a complete physical examination, including a neurological exam, to assess the horse's condition.

Diagnostic testing is a crucial step in identifying neurological horse diseases.

Blood tests can help diagnose conditions like equine protozoal myeloencephalitis (EPM), which is caused by a parasite that infects the central nervous system.

A veterinarian may perform a complete blood count (CBC) to check for anemia or other blood abnormalities.

The CBC can also help identify conditions like equine infectious anemia, which is a viral disease that affects the horse's immune system.

Magnetic resonance imaging (MRI) or computed tomography (CT) scans can be used to visualize the brain and spinal cord, helping to diagnose conditions like wobblers syndrome and botulism.

These tests can also help identify the location and extent of any damage or inflammation in the nervous system.

Electroencephalography (EEG) can be used to measure the electrical activity of the brain, helping to diagnose conditions like equine epilepsy.

EEG can also help identify abnormal brain wave patterns, which can be indicative of neurological disease.

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Wobbler Disease, also known as Cervical Vertebral Stenotic Myelopathy (CVSM), is a common cause of incoordination in young sport horses.

CVSM is a developmental abnormality affected by genetic and environmental factors, including diet, growth rate, workload, and injury.

The disease involves spinal cord compression due to structural abnormalities of the neck bones and joint spaces, joint or ligament instability, and soft tissue or bony changes of the neck.

In general, CVSM is divided into two categories: one affecting young horses with neck instability (type I), and the other affecting older horses with arthritic joint changes in the neck bones (type II).

Encephalomyelitis (EEE, WEE) is a serious mosquito-borne disease that affects horses, mules, burros, donkeys, and zebras in the Americas.

These viruses can also infect humans, birds, and occasionally other mammals, making it a significant public health concern.

The case fatality rate for some of these viruses can be as high as 90%, depending on the virus, host, and form of the disease.

No specific treatment is available for equine encephalomyelitis, making prevention and early detection crucial.

These viruses are spread by mosquitoes, which can be a challenge to control, especially in areas with high mosquito populations.

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Equine Herpes Myeloencephalopathy (EHM) is a serious neurological disease caused by equine herpesvirus (EHV).

EHM is very contagious and can have a mortality rate as high as 30%.

Equine herpesvirus is a common DNA virus that occurs in horse populations worldwide.

The two most common strains are EHV-1, which causes abortion, respiratory disease, and neurological disease; and EHV-4, which usually causes respiratory disease only but can occasionally cause abortion and rarely cause neurological disease.

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Protozoal Myeloencephalitis is a common neurologic disease of horses in the Americas.

It has been reported in most of the contiguous 48 states of the US, southern Canada, Mexico, and several countries in Central and South America.

The disease is caused by a protozoan, Sarcocystis neurona, which is ingested through contaminated feed or water.

Horses are infected by eating S neurona sporocysts, and the definitive host for S neurona in the US is the opossum.

Opossums become infected by eating sarcocyst-containing muscle tissue from an infected intermediate host, and after a brief period of 2-4 weeks, infectious sporocysts are passed in the feces.

This makes opossums a key player in the transmission of the disease to horses.

Wobbler Disease or Cervical Vertebral Stenosis is a common cause of incoordination in young sport horses.

It's a developmental abnormality affected by genetic traits and environmental influences, including diet, rate of growth, workload, and injury.

CVSM is widely considered to be a complicated condition with spinal cord compression due to structural abnormalities of the neck bones and joint spaces.

This compression mixes up the signals from the brain to the limbs or vice versa, leading to neurological signs.

CVSM is often divided into two broad categories: one affecting young horses with neck instability (type I), and the other affecting older horses with arthritic joint changes in the neck bones (type II).

There's substantial overlap between types, and older horses can have developmental abnormalities despite a late onset of clinical disease.

Very young horses can have bone remodeling that contributes to their clinical signs, making diagnosis and treatment challenging.

Older horses frequently develop bony changes in the neck without damaging the spinal cord or leading to neurological signs.

Degenerative Myeloencephalopathy is a condition that affects the spinal cord and brain. It's a progressive disease, meaning it gets worse over time.

This condition is characterized by the degeneration of the spinal cord and brain tissue. Symptoms include loss of motor function, muscle weakness, and ataxia.

Degenerative Myeloencephalopathy can be caused by various factors, including genetic mutations and environmental toxins. It's a rare condition, but it can have a significant impact on a person's quality of life.

Symptoms of Degenerative Myeloencephalopathy can include difficulty walking, balance problems, and numbness or tingling in the extremities. In severe cases, the condition can lead to paralysis and loss of bladder and bowel control.

Treatment options for Degenerative Myeloencephalopathy are limited, and there is currently no cure. However, medication and physical therapy can help manage symptoms and slow the progression of the disease.

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The prognosis for horses with CVSM is influenced by several factors, including age, severity of neurologic deficits, duration of neurologic signs, and owner expectations for performance.

Most horses with CVSM do not have life-threatening ataxia, but some may become unable to rise or demonstrate severe incoordination that warrants euthanasia.

Without treatment, the prognosis for substantial improvement in neurologic function is generally poor, as the underlying malformation or instability will continue to damage the spinal cord.

Medical treatment alone is unlikely to lead to long-term improvement in incoordination, although improvement in comfort can be observed in response to anti-inflammatory treatment.

Surgical stabilization provides the best long-term prognosis, with published studies estimating that approximately 75% of horses improved, and 45–60% achieved athletic function.

If owners are willing to consider surgical stabilization, this course should be pursued as soon as feasible after diagnosis to reduce cumulative injury to the spinal cord.

Riding a horse with ongoing neurological abnormalities increases the risk of stumbling or falling and thus injury to both rider and horse.