ZOONOTIC DISEASES

ZOONOTIC DISEASES ZOONOTIC DISEASES are diseases

caused by infectious agents that can be transmitted between or are shared by animals and humans.

Example : Rabies

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 .

Rabies

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, priapism & 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.

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