Rabies

RABIES

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

FIXED VIRUS

Variable long incubation period

Incubation period is fixed and short

Following intracerebral inoculation, death of rabbit occurs in 14 – 20 days

Death of rabbit occurs in 7 days

Negri bodies present

Absent

Salivary glands affected

Not affected

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.

Rabies - Clinical sign - Goat Rabies - Clinical sign - Dog

Rabies - Increased sexual libido - Goat

Rabies - Barking dog

  • 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

Rabies - Negri bodies

Rabies - Intra cytoplasmic inclusions in nerve cell - Negri bodies

  • 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)
Last modified: Monday, 19 March 2012, 5:44 AM