Canine Distemper Virus

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Morbilliviruses

Also known as CDV

Hosts

  • Dogs, ferrets, seals, lions, mink
  • Has been a major pathogen of dogs prior to vaccination

Pathogenesis

  • Aerosol infection
  • Infects alveolar macrophages or oropharynx
  • Multiplies in the bronchial and other lymph nodes, infects monocytes and dendritic cells
  • Viraemia
  • Spreads via monocytes to a variety of epithelium depending upon the strain of virus
  • Respiratory and alimentary tracts, skin and later (1-5 wk. post infection) to the brain
  • Clinical signs:
    • Mucopurulent oculonasal discharge
    • Keratitis
    • Interstitial pneumonia
    • Severe clinical pneumonia follows secondary infection with Bordetella bronchiseptica
    • Smelly sometimes bloody diarrhoea
    • Eruptions on the skin including hyperkeratosis of the nose and pads (hardpad)
    • Demyelination (especially in cerebellum) -> incoordination or muscle tremors -> paralysis and coma or convulsions -> death
    • Encephalitis
    • Secondary pyogenic infections associated with immunosuppression and damage to epithelia
    • Recovered animals may have persistent or spasmodic chorea
    • The severity of the disease may vary; if enough neutralising antibody develops in the early stages, the virus maybe kept restricted largely to the lymph nodes
  • Variable mortality depending on virulence
  • May occur subclinically
  • Involvement of central nervous system generally results in death

Diagnosis

  • May present as series of infections
  • Immunocytochemistry of inclusion bodies
    • Intracytoplasmic inclusions may be found in most affected tissues
    • Inclusions persist longest in the brain (may be intranuclear) and the alveolar macrophages
    • Sections of fixed bronchial tissue, lung, macrophages, bladder may be used or nasal or conjunctival epithelium from live animals
  • Giant cells may be seen in the alveoli

Control

  • Live attenuated virus vaccines given at 10 and 12 weeks of age
    • Some now given at 7 and 10 weeks to allow socialisation
  • Homeopathic vaccines do not work
  • Live attenuated vaccines may kill some wildlife therefore Iscom vaccine is used in seal sanctuaries

Secondary Concerns


Canine distemper

  • Caused by a morbillivirus
  • Rhinitis
  • Although many organs can be affected by CDV, a relatively constant feature is the respiratory signs which occur in varying severity
  • A syndrome of catharral oculonasal discharge, pharyngitis and bronchitis is relatively common in the initial stages
  • Since one of the primary sites of action of this virus is lymphoid tissue, the resultant immunosuppression -> predisposition to secondary bacterial infection
  • May cause interstitial pneumonia where inclusions are found within alveolar macrophages
  • Gross pathology:
    • Oedematous lungs, diffuse interstitial pneumonia
  • Micro pathology:
    • Necrosis of pneumocytes, necrotising bronchiolitis, alveolar oedema, thickening of alveolar walls and type II pneumocyte hyperplasia