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
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.