What are Meningitis and Encephalitis?
Meningitis and encephalitis are rare in adult horses, but foals are more susceptible because of their inability to rid the blood of bacteria. In adult horses, the blood-brain barrier blocks the bacteria to the brain and the cerebrospinal fluid. However, if a disease or infection close to the brain such as an ear or eye infection or a skull fracture, may lead to meningitis. It is essential to get a diagnosis and treatment from an equine veterinary professional right away to avoid permanent central nervous system damage.
Meningitis and encephalitis in horses are dangerous infections that cause inflammation in the spinal cord and brain. This disorder can be debilitating at the least, life threatening at the worst. Both meningitis and encephalitis are serious illnesses. The inflammation of the membranes around the spinal cord and brain are called meningitis and when the brain is inflamed it is called encephalitis. When both of these happen at the same time, it is called meningoencephalitis. Symptoms can range from mild headache to convulsions and death.
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Symptoms of Meningitis and Encephalitis in Horses
The symptoms of both meningitis and encephalitis are varied depending on what causes it.
- High body temperature
- Appetite loss
- Muscle spasms
- Bulging eyes
- Neck extension
- Scratching (severe itchiness)
- Stiff legs
- Tense neck muscles
- Leaning on stationary objects
- Drooping ears
- Abnormal chewing
- Sensitive to the touch
- Eyes pointing in different directions
- Droopy eyelid
- Rapid eye movement
- Bumping into things
- Abnormal behavior
- Wobbly gait
- Walking in circles
- Difficulty walking on hard surfaces
- Laying down more often
- Convulsions or seizures
- Encephalitis is inflammation of the brain
- Meningitis is inflammation of the membranes of the spinal column and brain
- Meningoencephalitis is the inflammation of the brain and the membranes around the brain and spinal cord
Causes of Meningitis and Encephalitis in Horses
The cause of meningitis and encephalitis can vary. Some of the most common include:
- Arbovirus (West Nile)
- Bacteria (Actinomyces, Bacteroides, Escherichia coli, Eubacterium, Fusobacterium, Nocardia, Pasteurella multocida, Peptostreptococcus anaerobius, Propionibacterium, Staphylococcus, Streptococcus)
- Injury to head or spine
- Virus (alphavirus and flavivirus)
Diagnosis of Meningitis and Encephalitis in Horses
Your veterinarian will ask for your horse’s background and medical history, including vaccinations and symptoms. A physical examination is done first which includes blood pressure, body temperature, weight, height, heart rate, respirations, body condition score, lung sounds, abdominal palpation, and eye examination. A neurologic examination is done next by first watching your horse’s behavior from a distance and then up close. The veterinarian will then check the reflexes. Movements are evaluated next by having you walk your horse back and forth and in a circle to look for any abnormalities, foot dragging, foot placement, limb crossing, and balance problems.
Cerebrospinal fluid collection and analysis (spinal tap) is done by inserting a 6 to 8-inch hypodermic needle into the lumbosacral space in the hip (standing) or in the atlanto-occipital space in the neck under general anesthesia, testing this fluid that surrounds and bathes the spinal cord and brain for bacteria. If the fluid is cloudy, the veterinarian will do a special microscopic analysis. A complete blood check (CBC) is necessary to detect abnormally low lymphocytes (white blood cell). Bacterial and fungal cultures will also be done to check for bacteria or fungi. Also, an IgM capture ELISA is one of the best tests for meningitis and encephalitis. Imaging tests are also important, including a CT scan (computed tomography) and magnetic resonance imaging) MRI. These can show signs of a stroke, spinal stenosis, brain damage, injury, herniated discs, blood clots, and more. In addition, an electroencephalography (EEG) can be performed to find abnormal electrical activity.
Treatment of Meningitis and Encephalitis in Horses
There are many treatments depending on the cause. Some infections require medication, others need medication and treatment or support. Other times, there are no treatments and the only thing you can do is offer palliative care to control inflammation and pain.
A broad spectrum antibacterial can get past the blood brain barrier with anti bactericidal drugs, which are used over bacteriostatic medications. Some of these medications are cephalosporins, ampicillin, and penicillin. For a viral infection, antivirals are given such as acyclovir, ceftriaxone, and interferon. Some antiprotozoal drugs that are approved for horses are ponazuril and diclazuril. A high dosage of methylprednisolone or dexamethasone may control severe complications such as brain herniation and cerebral edema.
This can include treating anything from pain, fever, and stiffness. Medication, fluid therapy, and nutritional therapy may all be used or just one of these, depending on the situation.
Recovery of Meningitis and Encephalitis in Horses
Prognosis depends on what caused your horse to get meningitis or encephalitis. With bacterial meningitis, the fatality rate is high (about 95%) by the time symptoms appear. Other forms have a guarded prognosis. The younger the horse, the better the chances for survival.