Viral infection of
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Viral diseases of the nervous system are seen
in four main patterns:
• Viral meningitis, characterized by the development of lymphocytic meningitis.
• Cytolytic, in which there iscell destruction producing encephalitis or
myelitis. This is the most clinically severe pattern of involvement, most
commonly seen with herpes simplex.
• Latent, in which virus is integrated into the host cells, with the potential
for re-activation as a cytolytic infection. This is extremely
common with herpes zoster, causing shingles.
• Persistent, in which there is slow, smouldering degeneration of neuronal
tissues caused by viral infection in the absence of elimination by
immuneresponses,e.g. measles virus infection causing subacute sclerosing
AIDS commonly affects the nervous system
One of the most common causes of viral infection of the nervous system is HIV.
Not only does HIV directly affect the brain and spinal cord, AIDS also
predisposes to several complications due to immunosuppression.
The AIDS dementia complex (HIV cognitive/motor complex)} is a clinical syndrome
that has elements of intellectual impairment, and behavioural and motor changes.
Several pathologically defined changes underlie this clinical syndrome.
Lymphocytic meningitis is seen in patients around the time of seroconversion and
is defined as occurring in the absence of any demonstrable opportunistic
HIV encephalitis is a multifocal process characterized by inflammatory foci
including multinucleate giant cells, mainly seen in white matter, basal ganglia
and brain stem.
HIV leukoencephalopathy is characterized by myelin loss, gliosis, phagocytic
macrophages and scattered multinucleate giant cells in white matter. There is
little or no inflammatory infiltration.
Diffuse poliodystrophy is the term applied to neuronal loss, microglial
activation and gliosis in CNS grey matter.
Vacuolar myelopathy is the term used to describe vacuolation in myelin sheaths,
with myelin loss in spinal cord.
Cerebral vasculitis is seen most prominently in childhood HIV disease of the
Spongiform encephalopathies are caused by an unconventional protein-only agent
and can be genetic as well as transmissible
Creutzfeldt-Jakob disease is an uncommon nervous system disorder. It is
characterized by accumulation of a modified normal cell-membrane protein, termed
'prion protein' (PrP). The precise way in which the protein is modified is
The disease is associated with a rapidly progressive dementia in humans, with
histological vacuolation in the brain, known as spongiform encephalopathy. It is
similar to kuru in humans, scrapie in sheep and bovine spongiform encephalopathy
in cattle, which also accumulate PrP. As these diseases were once thought to be
caused by a virus with a long incubation, they were formerly termed 'slow-virus
Although most human disease is sporadic, cases have resulted from
transplantation of tissue from an affected person, as well as from
administration of growth hormone derived from cadavers. Identical and
transmissible disease results from hereditary mutations in the gene coding for
the prion protein in man (Gerstmann-Straussler syndrome, causing familial cases
of ataxia and dementia).
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We give here simplified and accurate information about the disease
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