Canine Distemper Virus

Description

Canine distemper is a contagious, febrile disease of canids and other carnivores caused by Canine Distemper Virus. Canine distemper virus is a member of the paramyxoviridae family and the morbillivirus genus, and as such is closely related to the measles, rinderpest and phocine and dolphin distemper viruses.

   * Viruses of Paramyxoviridae are enveloped - many are pleomorphic - and have a helical nucleocapsid (see Fig. 18.1).
   * Genomes are single-stranded, negative-sense, non-segmented RNA.
   * The envelope is covered with spikes whose glycoproteins are responsible for hemagglutinin, neuraminidase, and hemolytic activities.
   * Replication takes place in the cytoplasm and envelopment at the surface (plasma membrane) of infected cells.
   * The ssRNA (-) is used as a template for the production of mRNA (+) and progeny genomes.
   * The viruses are generally sensitive to heat, drying, lipid solvents and many disinfectants.
   * Most can be propagated in embryonated eggs and in cell cultures with the production of cytopathic effects including syncytia and cytoplasmic inclusions.

• 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

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

• 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

Signalment

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

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 alveol

Treatment

• 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