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Rabies viruses are a
RNA viruses of the genus Lyssavirus and the family Rhabdoviradae.
Rabies remains as
one of the most feared zoonotic diseases in the world.
In humans it is a lethal
encephalitis.
Carnivores, such as the dog, wolf, fox, and skunk, are
the principal reservoirs, but the infection extends to bats and to
some domesticated animals, such as cattle, goats, and swine.
The
infectious agent is transmitted to humans through contaminated saliva
introduced into the wound of a bite.
The virus enters a peripheral
nerve and is transported by centripetal axoplasmic flow to the spinal
cord and brain.
The latent interval varies in
proportion to the distance of transport, being as short as 10 days or
as long as 3 months.
Centrifugal intra-axonal transport of
the virus contaminates visceral organs, particularly the salivary
glands, which in turn contaminate the
saliva.
Although it is
not understood why the virus seeks out the brain stem, this pattern of
localization initiates the classic symptoms of difficulty in swelling
and the painful spasms of the throat that justify the term hydrophobia.
The clinical
symptoms include irritability, agitation, seizures, and
delirium and reflect a general
encephalopathy.
The spinal
cord is altered in accord with the “typical viral response” : a modest pleocytosis
by lymphocytes, a moderate elevation of protein content (15 to 100
mg/ml), and an unaltered glucose level and spinal fluid pressure.
The illness progresses to death within
one to several weeks.
Grossly the brain and spinal
cord show edema and petechial hemorrhages. Involvement of the spinal
cord is most conspicuous when the portal of entry is on the lower part
of the body.
Lymphocytes
aggregate about the small arteries and veins in the brain stem.
Scattered neurons show chromatolysis and neuronophagia.
Glial nodules
attest to the infectious nature of the process.
The geographic
distribution of the inflammation, centered in the brain stem with
spillage into the cerebellum and hypothalamus, strongly suggests
rabies.
Image
Link1 ;
Image Link2
In about 75% of cases Negri
bodies can be seen on hematoxylin and eosin stained sections.
Negri
bodies: click here
The control of
rabies largely depends on the prevention of infection of dogs and cats
by vaccination in endemic areas and the control of their movement,
including measures of quarantine and vaccination, in rabies-free
countries. |
