3.4 NEUROLOGICAL DISEASES OF OLD AGE CHRONIC 'OLD DOG'
Canine distemper is most prevalent in young dogs, but chronic 'old dog' encephalitis
is the neurological manifestation of canine distemper virus (CDV) infection that
is seen in adult dogs which have survived the acute infection. Dogs developing this
condition are usually over 6 years of age and have serological evidence of systemic
The neurological signs (see Table 3.4) may occur without previous evidence of systemic
disease and are usually progressive and irreversible (Greene and Appel 1990; Skerritt
1989). The involuntary muscle twitching (myoclonus) is typical of CDV infection.
CSF examination for increased protein and increased lymphocyte count may be helpful
in diagnosing dogs exhibiting neurological signs.
Histologically there is perivascular lymphoplasmacytic infiltration in areas of demyelination
and neuronal degeneration which may progress to
sclerosing panencephalitis in more chronic cases. Canine distemper virus inclusion
bodies are present in epithelial and other cells but their sigis not clear (Greene
& Appel 1990).
Distemper can occur after stress, during concurrent illness or in immunesuppressed
vaccinated dogs. Although vaccination with modified live CDV may confer long-term
active immunity to some individuals, most manufacturers recommend booster vaccinations
at 1-2 year intervals to ensure adequate ongoing protection.
The long-term prognosis is poor for most cases and, although some authors advocate
a period of 1-2 weeks supportive therapy, euthanasia is usually the eventual outcome.