Synonym: LYSSA, HYDROPHOBIA ,RAGE
Definition
- Acute viral infection in man and other warm blood animals characterized by abnormal behaviour, nervous disturbances, ascending paralysis, impairment of consciousness and death.
Aetiology
- RNA Virus – Rhabdoviridae
Incidence
- Rabies has been recorded in various parts of the world.
- In Asia, Africa, Latin America and the middle east , rabies is endemic
- Australia, New Zealand, Hong Kong, Singapore, Britain, Hawaii – free from Rabies
Street virus is that found in natural cases and passage through rabbits increases its virulence and is called fixed virus
STREET VIRUS
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FIXED VIRUS
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Variable long incubation period
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Incubation period is fixed and short
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Following intracerebral inoculation, death of rabbit occurs in 14 – 20 days
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Death of rabbit occurs in 7 days
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Negri bodies present
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Absent
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Salivary glands affected
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Not affected
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Suscepibility
- Extremely susceptible: Dog, fox, wolf, jackal, cat, mongoose, bat.
- Moderately susceptible: Cattle, goat, sheep, horses,
- Cattle and equine – Dead end host
- Vampire bats acts as a vector.
Incubation period : Depends on the site of the bite. The nearer the bite to the head, the shorter the incubation period. It may vary from 2 weeks to 9 months.
Transmision
- By bite of an affected animal
- Since the virus is present in the saliva, infection by flies is facilitated
- Licking of the wound by the rabid dog may also result in infection
- Haematogenous spread
- Infection may be spread to the foetus in utero from an affected bitch
Pathogenesis
- After the bite, virus deposited in the wound through a break in the skin
- Local replication of virus in epithelial cells and myocytes
- Cross neuromuscular spindles
- Move centripetally through the nerves
- Reach Central Nervous System
- After reaching the brain, it parasitizes the ganglion cells, grows and then spreads through various nerves that emanate from the centrifugal fashion
- Virus has got great affinity for salivary glands and s o virus spreading along the nerves that supply the salivary glands, the facial (vii) and glossopharyngeal (ix) nerves and from there it is excreted through saliva
- In CNS: Virus damage the nerve cell and vascular endothelium
- Irritation of nerve cells
- Increased excitability (Furious form)
- Neurons of medulla ( Fever, polyuria, glycosuria)
- Neuronal degeneration
- Paralysis of muscles of deglutination unable to swallow / Dribbling of saliva
- Paralysis of jaw muscles , jaws cannot close and so hang down -Dropped jaw
- Paralysis of respiratory muscles – Asphyxia and death
Clinial signs
- Furious form
- Excited, animal goes into rages ( violent anger), indiscriminate biting, barking at imaginary objects, chews inanimate objects, red eye – Vacant look, champing of jaws, dribbling of saliva, change of voice.
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Rabies - Increased sexual libido - Goat
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Rabies - Barking dog
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- Dumb form (Paralytic form)
- Sick, sluggish, progressive weakness, vacant look, does not obey orders, does not recognize family members, try to hide in corners and under the cot
- Death is 3 to 4 days after onset of symptoms (or) atleast within 10 days.
- Horse: Colic
- Cattle: Bellowing
- Cat -Furious form only
- Rabbit: Dumb form only
- Bull and rams may show sexual urge
Gross lesions
- Limited only to CNS
- Hyperaemia, oedema with petechiae of meninges
Microscopic lesions
- Non suppurative encephalitis
- Perivascular cuffing by lymphocytes
- Microglial cell proliferation and form small nodules – "BABES NODULE "
- Satellitosis around ganglion cells
- Degeneration of ganglion cells – Neuronophagia seen in hippocampus, brain stem Similar changes in cerebrospinal and sympathetic ganglia
- Ganglioneuritis of paravertebral ganglion
- Acute catarrh of respiratory and digestive tract
- Hyperemia of kidney, spleen, liver and salivary gland
- Negri bodies: Intracytoplasmic inclusion bodies found in Neurons
- In dogs – Hippocampus impressioin smear
- Cattle – purkinje cell of cerebellum impression smear
- Aggregate of virus
- Round/oval/acidophilic (magenta red) with basophilic granules
Clinical signs
- Under observation of rabies
- Impression smear of Hippocampus stained by seller’s (or) modified Mann’s method or Williams modification of von Gieson method
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Rabies - Intra cytoplasmic inclusions in nerve cell - Negri bodies
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- Habel’s mouse Inoculation test: Make an emulsion of piece of ammon’s horn and dilute 20 times with sterile water. This may be incubated with an antibiotic for ½ hour. 0.03 ml of this emulsion is injected intracerebrally into 6 mice. On the 5th, 6th and 7th days one mouse is sacrificed and the brain is examined for negri bodies. Negri bodies is usually seen on the 5thand 6th days
- A biological test, injecting the brain tissue into rabbits intracranially can also done for conformation
- Corneal or saliva test (FAT)
- Fluorescent Antibody Test FAT)
- Immunoperoxidase Test (IPT)
- Complement Fixation test (CFT)
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