Zoonotic diseases

 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
System.
 Transmitted to man by either licks or bites of a rabid
animal-mostly dogs.
 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 .

Causative Organism:
Rhabdoviruses are always
associated with Rabies.

Rhabdoviruses
• 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
sense RNA.

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
intolerable thirst.
 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.

PATHOGENESIS :
 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.

CONTD.
 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
near legs.

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
convulsions, hallucinations.
 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
urine.
 If facilities are available , then detection of rabies
virus RNA by reverse transcription PCR is a very
sensitive method.

Zoonotic diseases

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Zoonotic diseases