Canis ISSN: 2398-2942

Rabies disease

Contributor(s): Alex Morrow, Bryn Tennant, Julien Bazelle

Introduction

  • Cause: viral disease of the central nervous system (CNS).
  • Signs: 'furious ' and 'dumb' forms.
  • All mammals susceptible (to a variable extent). Birds less susceptible.
  • Reservoir hosts vary with country, but mainly include dogs, cats, foxes, bats, raccoons and wolves.
  • Treatment: none.
  • Diagnosis: signs, history of exposure to the virus, confirmation on examination of brain at histopathology.
  • Prognosis: grave/hopeless.

Pathogenesis

Etiology

Predisposing factors

General

  • All mammals susceptible to infection (to a variable extent). To a lesser degree birds can be susceptible too.

Specific

  • Bite/scratch from infected animal.
  • Contact with saliva from infected animal, especially if skin damaged.

Pathophysiology

  • Transmission by bite/scratch or accidental break in skin.
  • Primary replication in muscle fibers at site of inoculation → virus aggregates around proprioreceptor nerve endings → virus binds to nicotinic acetylcholine receptors and enters axon sheath of afferent nerve within 5 hours → virus migrates (retrograde axoplasmic flow) to spinal ganglion at up to 3 mm/h → multiplies in spinal ganglion (or hippocampus) → virus enters dorsal horn of spinal cord → ependymal cells → brain → centrifugal spread down cranial nerves → salivary glands (and lungs/kidneys) → multiplication → excretion in saliva in 50% of infected dogs (others die before this stage).
  • Combined active and passive immunization shortly after exposure eliminates virus before it reaches CNS.
  • Some exposed dogs do not develop disease (immunity?).

Timecourse

  • Incubation period depends on:
    • Distance of site of inoculation from CNS.
    • Severity of bite.
    • Dose of virus inoculated.
  • Incubation 5 days-12 months (usually less than 3 months).
  • Death within 5-15 days of onset of signs.

Epidemiology

  • Dog requires high virus dose for infection ('intermediate susceptibility'), puppies more susceptible than adults.
  • Infection by inhalation very rare.
  • Reservoir host varies with location: include Canidae, Mustelidae and Chiroptera (bats).
  • Endemic in racoons, skunks (USA), vampire bats (Central America), mongoose (S. Africa - parts of Caribbean), red fox (Europe), Jackals (Africa).
  • Dog rabies is most significant in zoonosis.
  • Bats may have subclinical infection with persistent viremia.
  • Skunks and foxes may recover from infection.
  • Some dogs have mild symptoms, recover, and remain as persistent excretors.
  • Some countries free of rabies (see above).
  • Virus survives only when numerous susceptible hosts available in close contact.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

Other sources of information

  • Beynon P H & Edney A T B (1995) Rabies in a Changing World. In: Proceedings of a Joint Symposium held at the Royal Society of Medicine, London. 3rd May. Cheltenham: British Small Animal Veterinary Association.


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