Inflammation of the meninges, the membranous covering of the brain and spinal cord (meningitis), and inflammation of the brain (encephalitis) often are seen simultaneously (meningoencephalitis), although either can develop separately. Causes of meningitis, encephalitis, and meningoencephalitis include infection by bacteria, viruses, fungi, protozoa, rickettsia, or parasites. In some cases, the immune system is involved, chemical agents cause the inflammation, or the cause is unknown. In dogs, especially adult animals, viruses, protozoa, rickettsia, and fungi are more frequent causes of meningitis and encephalitis than are bacteria.
Meningitis and encephalitis are less common than infections of other organs, because the nervous system has protective barriers. However, infections may occur when these protective barriers are injured or weakened. Infections can also spread to the central nervous system from the sinuses, the inner ear, vertebrae, or spinal disks; these infections may result from migrating foreign material (eg, grass awns), bite wounds, or other traumatic injuries near the head or spine. Brain abscesses also can arise from direct infections or from blood poisoning. Bacterial meningitis or meningoencephalitis is not common in dogs and is not generally contagious.
The usual signs of meningitis are fever, neck pain and rigidity, and painful muscle spasms. Dogs may have these signs without any sign of brain or spinal cord dysfunction. However, in widespread meningoencephalitis, depression, blindness, partial paralysis of the face or the limbs, loss of balance or motor control, seizures, behavioral changes, agitation, head tilt and circling behavior, difficulty eating, and loss of consciousness (including coma) can develop, depending on the severity and location of the inflammation. The analysis of cerebrospinal fluid from a spinal tap is the most reliable and accurate means of identifying meningitis or encephalitis. Additional tests may be necessary to identify the cause of disease.
Cases resulting from an immune system disorder can be treated with corticosteroids or other medications that alter the immune system. Infections caused by rickettsia, protozoa, and certain bacteria can be treated with appropriate antibiotics, and fungal infections can be treated with specific antifungal drugs. The outlook for recovery depends on the cause, the severity of the infection, and whether or not the infection has resulted in irreversible damage to the nervous tissue. Supportive care may include pain relievers, anticonvulsant drugs, fluids, nutritional supplements, and physical therapy.
Also see professional content regarding meningitis and encephalitis.