The meninges are the lining layers surrounding the brain and spinal cord- the central nervous system. Meningitis refers to inflammation (usually caused by bacterial or viral infection) of this lining. Meningitis is a very rare condition in the adult horse.

In order for infection of the meninges to take place, bacteria or virus must gain access to the central nervous system. Some viruses readily gain access.

Bacterial penetration is more difficult and this is why bacterial meningitis is so rare. Because of the protection of skull and spinal column, penetrating wounds into the central nervous system are rare. The central nervous system is also protected by something called the blood-brain barrier, which is a buffer between these two compartments that generally isolates the brain from blood infections.

Meningo-encephalitis is more common in foals because of their reduced ability to clear bacteria from the bloodstream (septicemia). In foals, unlike adults, bacteria are usually introduced to the brain via the bloodstream. In septicemic neonatal foals, there may also be further breakdown of the blood brain barrier, and bacteria present in the bloodstream are able to gain access to the central nervous system, enabling infection.

In normal healthy adult horses, the blood-brain barrier prevents access of bacteria to the brain itself and to the cerebrospinal fluid. But disease processes close to the brain and spinal cord can lead to meningitis. Examples of this are severe inner ear infections, skull fractures open to the sinus. and advanced bacterial eye infections that can actually infect the brain through the optic nerve.

DIAGNOSIS requires vet physical and neurologic exam, and requires analysis and culture of cerebrospinal fluid for confirmation.

TREATMENT is usually aggressive antibiotics, hopefully (but not always) guided by culture and sensitivity.