ZOONOTIC DISEASES are diseases caused by
infectious agents that can be transmitted
between or are shared by animals and humans.
Example : Rabies
Acute, highly fatal viral disease of Central Nervous
Transmitted to man by either licks or bites of a rabid
Rabies infects both domestic and wild animals
alike, and is then spread to people through close
contact of the infected saliva of these animals , i.e., by
bites or scratches.
This disease is present all over the world, but Asia and
Africa has almost 95% human fatality .
Rhabdoviruses are always
associated with Rabies.
• Bullet shaped virus.
• Belongs to genus Lyssavirus.
• 180*75nm length, with one end rounded conical
and other end concave.
• Has a lipoprotein envelope, that carries spikes.
• Spikes consists of glycoprotein G; and are not
present at planar end of the virus.
• The genome of the virus is unsegmented linear –ve
COMMON FACTS ABOUT RABIES
The name ‘Rabies’ comes from:
Latin : Rabidus – Mad
Sanskrit : Rabhas - Frenzy.
The disease of rabies in human is called
Hydrophobia, because the patient exhibits fear of
water, being incapable of drinking though subject to
In 1881, Pasteur established that rabies virus was
present in the brain of the infected animals.
In 1885, a 9 year old boy was bitten by a rabid
dog, and was administered a course of 13
inoculations of the infected cord
vaccine, i.e., injections of graded infectivity of the
virus; The boy survived. This was a milestone in
development of vaccines.
Virus multiplies in the muscles, connective tissues
or nerves at the site of bite for 48-72 hours.
It then penetrates the nerve endings and travels in
the axoplasm towards the spinal cord and brain.
Virus moves in the axons at a speed of 3mm/hr.
Infection spreads centripetally from axon to
neuronal bodies, and progressively up the spinal
cord through synapses of neurons.
Virus ascends rapidly to brain, while multiplying &
spreads long the nerve trunks to various parts of
body, including salivary glands.
The virus then again starts multiplying in the
salivary glands and is then shed in saliva.
When the virus ultimately reaches all the tissues
in the body, it leads to fatality.
The virus may also be shed in milk and urine.
Though viremia is not clinically significant.
Incubation Period : 1-3 months.
could be as short as 7 days,
could also extend up to 3 years.
Incubation period is short in the persons bitten on
faces and head, and longer in the persons bitten
STAGES OF RABIES ~ 4 STAGES
PRODROME : Fever, headache, malaise, fatigue &
anorexia, apprehension, anxiety, irritability, insomnia, priapis
m & excessive libido. Lasts for 2-3 days.
ACUTE ENCEPHALITIC : Hyperactivity, bouts of
bizarre behaviour, agitation, seizures, Hydrophobia, only dry
solids could be eaten, pharynx & larynx starts gagging and
choking, patients even dread the sight of water, death
occurs within a week due to respiratory
PARALYSIS : some patients then go paralytic due to
muscle spasms and seizures, while some slip into coma.
DEATH: After the stage of paralysis, patients die, due to
respiratory arrest and other complications.
LABORATORY DIAGNOSIS :
Diagnosis may be made by postmortem by the
demonstration of negri bodies in the brain.
Isolation of virus by intracerebral inoculation of mice
can be attempted from the brain, CSF, saliva and
If facilities are available , then detection of rabies
virus RNA by reverse transcription PCR is a very