The brain is protected by tissue membranes called meninges. Meningitis is the inflammatory condition affecting these membranes, while encephalitis is the inflammatory condition of the brain tissue. Both these conditions may occur together, and may be referred to as meningoencephalitis, but they may occur independent of each other too.
Meningitis as well as encephalitis in dogs can be caused by bacterial, rickettsial or viral infections. Protozoa and fungi can also cause inflammation in the brain and the meninges. Parasitic infestations occasionally result in these inflammatory conditions when the larvae of the parasites reach the brain, or make cysts in the nerve tissues. In some cases, the cause cannot be identified, or auto immune disorders are suspected. Bacterial infection is rarely the cause of encephalitis or meningitis in dogs; but fungal and viral infections as well as rickettsia and some protozoa are more likely to cause such inflammations. When bacterial meningitis occurs in dogs, though they rarely do except in young dogs, they are usually non-contagious.
Nervous system infections are comparatively rare, as the nervous system has several protective measures to keep it safe from the invasion of disease causing agents, but when these barriers are weakened, they may be breached by the pathogens. Penetrative injuries from bites or sharp objects can introduce infective agents into the sterile environment of the brain and the spinal cord. Infections present in the vertebrae or the disks between them, inner ear infections and sinus infections may spread to the meninges or the brain. Fractures of the vertebrae or the skull put the spinal cord and the brain at risk. Blood poisoning and infections that spread through nerves can directly cause these disorders.
The symptoms of meningitis include fever as well as rigidity and pain in the neck. They may be accompanied by muscle spasms that are usually painful. Other than these symptoms, the dog may not display any of the characteristic symptoms of brain and spinal cord dysfunction. But central nervous system disorders such as loss of motor control, facial paralysis, blindness, agitation and other behavioral alterations, circling, head tilt, paralysis of forelimbs or hind limbs etc., may occur with meningoencephalitis. The dog may become depressed, and lose interest in food or have difficult in eating. Seizures and fainting may occur, and it may progress to coma. The severity of the symptoms is related to the location of the inflammation as well as its extent. When dogs display these symptoms, a spinal tap is done to draw the cerebrospinal fluid which can be tested for these inflammatory conditions and to identify the possible cause.
Antibiotic treatments are generally effective against the bacteria, rickettsia or protozoa causing the infections. Anti-fungal medication can be used after identifying the fungal species responsible for the inflammation. If autoimmune disorders are the cause of meningitis or encephalitis, corticosteroids are administered. Besides reducing inflammation, they may alter the mechanisms of the immune system too.
During the treatment period, the dog may require supportive care such as fluid supplementation and other nutritional inputs. Physiotherapy may be prescribed to keep the paralyzed body parts, if any, in good health. Anticonvulsants and pain relievers may be given, if necessary. The prognosis greatly depends on not only the type of infection or injury the dog has sustained, but also on whether irreversible damage has taken place. Early detection as well as prompt and intensive treatment may result in good outcomes.