Felis ISSN 2398-2950

Rabies

Contributor(s): Stephen Barr, Severine Tasker

Introduction

  • Virus disease of the central nervous system (CNS).
  • All mammals susceptible.
  • Reservoir hosts vary with country.
  • Signs: 'furious' and 'dumb' forms: furious form far more common in cats.
  • Treatment: none.
  • Prognosis: grave/hopeless.

Pathogenesis

Etiology

  • Lyssavirus   Lyssavirus (rabies)  strain variation: antigenic variation and antigenic drift.

Predisposing factors

General

  • All mammals susceptible to infection.

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: includeCanidae,MustelidaeandChiroptera(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.
  • 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

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