Encephalitis (Brain Infection)
Encephalitis is an inflammation of the brain. Symptoms include fever, depression, behavior and personality changes (especially aggression), uncoordinated gait, seizures, stupor, and coma.
Canine distemper is the most common cause of encephalitis in dogs. Signs develop two to three weeks after the onset of the disease. Other causes of viral encephalitis include rabies, pseudorabies, and herpesvirus. Rabies is a very serious disease, but with present-day vaccination programs the disease is not common among domesticated animals. Canine herpesvirus produces an encephalitis in puppies younger than 2 weeks of age.
Bacterial encephalitis is caused by organisms that enter the brain via the circulatory system, such as bacterial endocarditis, or by direct extension from an infected sinus, nasal passage, or an abscess in the head or neck. Migrating foreign bodies such as porcupine quills or grass awns may get into the central nervous system. Fungal brain infections (caused by cryptococcosis, blastomycosis, or histoplasmosis) are rare causes of encephalitis, as are protozoan infections. Tick-borne rickettsial diseases, notably Rocky Mountain spotted fever and canine ehrlichiosis, are infrequent causes. These diseases may also involve the spinal cord.
Postvaccination encephalitis is rare with modern vaccines. It was most likely to occur when modified live virus distemper vaccine was administered at the same time as modified live parvovirus vaccine in puppies less than 6 to 8 weeks old. This is not usually seen with current vaccines and vaccination schedules.
Lead encephalitis is seen primarily in young dogs who chew on materials that contain lead, such as paint and drywall, especially in older buildings. Lead alters brain metabolism and causes inflammation and swelling. Central nervous system signs are often preceded by vomiting, diarrhea, or constipation. The diagnosis is confirmed by an elevated blood lead level.
Meningitis is an infection of the surface of the brain and spinal canal. It is caused by infected bite wounds about the head and neck and bacterial infections that travel to the brain from the sinuses, nasal passages, or middle ears. Aseptic meningitis isa nonbacterial disease of unknown cause. It affects large-breed dogs 4 to 24 months of age.
The diagnosis of encephalitis or meningitis is based on analysis of cerebrospinal fluid obtained by spinal tap. Serologic tests may identify the cause of the inflammation.
Treatment: Corticosteroids are used to reduce inflammation and swelling of the brain. Seizures are controlled with anticonvulsants. Antibiotics are used to treat bacterial infections. Rickettsia are extremely sensitive to tetracycline and doxycycline. Dogs who recover from encephalitis may develop seizure disorders and other neurological symptoms. Rabies is almost always fatal.
This common inflammatory brain disease in dogs is abbreviated GME. The cause is unknown. Female dogs of small breeds, especially terriers, Dachshunds, Poodles, and Poodle crosses, are predisposed. Although GME can occur at any age, most affected dogs are 2 to 6 years of age.
A chronic form of GME called Pug encephalitis occurs as an inherited disease in Pugs between the ages of 9 months and 4 years. It often begins with seizures, confusion, and loss of memory. This form of the disease has also been seen in Yorkshire Terriers and Maltese.
GME can affect all parts of the brain (the disseminated form), or only specific areas (the focal form). There is a rare ocular form that targets the optic nerves of the eyes.
The disseminated disease appears suddenly and progresses over a matter of weeks. It is characterized by incoordination, stumbling, falling, circling, head tilt, seizures and, dementia.
The focal disease begins with symptoms such as those of a brain tumor. Behavior and personality changes may predominate. The focal disease progresses to the disseminated disease over a period of 3 to 6 months.
The ocular disease is characterized by sudden blindness with a dilated pupil. It progresses to the disseminated disease more slowly than does the focal disease.
GME can be suspected when a toy dog such as a Poodle inexplicably develops confusion, disorientation, seizures, or other neurological signs that progress rapidly over a matter of weeks. A spinal tap with analysis of cerebrospinal fluid helps confirm the diagnosis. A CAT scan or MRI is useful in determining the form and location of the disease.
Treatment: Corticosteroids and immunosuppressive drugs may slow the progression of GME and provide temporary relief for several months. However, GME is almost invariably a progressive and fatal disease.
This article is excerpted from “Dog Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.
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