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Brain Diseases in Dogs

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.

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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.

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