Canine Distemper Virus

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

• Can contribute to Infectious Canine Tracheitis
• May be involved in chronic interstitial pancreatitis
• May cause growth retardation lattice
• May also trigger latent Toxoplasmosis due to suppressing effect on lymphoid tissue

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