Canine Distemper Virus

PARAMYXOVIRIDAE

VIRUSES

Hosts

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

Pathogenesis

• Variable mortality depending on virulence
• May occur subclinically
• Involvement of central nervous system generally results in death
• 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.

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