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Rabies

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Introduction

  • Viral disease of the central nervous system (CNS).
  • 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.
  • Signs: 'furious' and 'dumb' forms: furious form far more common in cats.
  • Diagnosis: signs, history of exposure to the virus, confirmation on examination of brain at histopathology.
  • Treatment: none.
  • Prognosis: grave/hopeless.
Print of the owner factsheet Rabies Owner Factsheet to give to your client.

Pathogenesis

Etiology

Predisposing factors

General

  • All mammals susceptible to infection. To a lesser degree birds can be susceptible too.

Specific

  • Rabid animals are the only source of rabies infection.
  • Infection acquired via 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 proprioceptor nerve endings   →   virus binds to nicotinic acetylcholine receptors and enters axon sheath of afferent peripheral nerve within 5 hours   →   no longer at site of inoculation within 10 hours   →   virus migrates (retrograde axoplasmic flow) to spinal ganglion at up to 3mm/hour   →   multiplies in spinal ganglion (or hippocampus)   →   virus enters dorsal horn of spinal cord   →   ependymal cells   →   brain   →   centrifugal spread down cranial nerves   →   salivary glands   →   multiplication   →   excretion in saliva (cat NOW infectious) (some cats die before this stage)   →    virus widely disseminated throughout organs.
  • Combined active and passive immunization shortly after exposure eliminates virus before it reaches CNS but national public health regulations usually mean post-exposure vaccination of cats is not allowed.
  • Rarely exposed cats do not develop disease (immunity).

Timecourse

  • Incubation period depends on:
    • Distance of site of inoculation from CNS; the further this is, the longer the incubation period.
    • Severity of bite.
    • Dose of virus inoculated.
  • Incubation 5 days-12 months (usually less than 3 months) and is usually shorter in cat than dog.
  • Death within 5-15 days of onset of signs.

Epidemiology

  • Cat requires high virus dose for infection ('intermediate susceptibility'); kittens more susceptible than adults.
  • Infection by inhalation very rare.
  • Reservoir host varies with location: include CanidaeMustelidae and Chiroptera (bats).
  • Endemic in raccoons, skunks (USA), vampire bats (Central America), mongoose (S. Africa), red fox (Europe), fruit bats (Australia).
  • Dog rabies is most significant in zoonosis but cats still important. Due to their explorative behavior, cats may be more exposed to infected wildlife.
  • Bats may have subclinical infection with persistent viremia.
  • Skunks and foxes may recover from infection.
  • 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

  • Recent references from PubMed and VetMedResource.
  • Frymus T, Addie D, Belák S et al (2009) Feline rabies. ABCD guidelines on prevention and management. J Feline Med Surg 11 (7), 585-593 PubMed.
  • Mansfield K L, Burr P D, Snodgrass D R et al (2004) Factors affecting the serological response of dogs and cats to rabies vaccination. Vet Rec 154 (14), 423-426 PubMed.
  • Esh J B, Cunningham J G & Wilkor T J (1982) Vaccine induced rabies in four cats. JAVMA 180 (11), 1336-9 PubMed.

Other sources of information

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

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