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. The Paramyxoviridae have a helical nucleocapsid surrounded by an envelope which possesses spiked glycoproteins responsible for haemagglutinin, neuraminidase and haemolytic activities. The genome of the Paramyxoviridae is single-stranded, negative-sense RNA which is used as a template for the production of messenger (positive-sense) RNA and further genomic material. Paramyxoviridae are sensitive to heat, dessication and most disinfectants, and so are not resistant in the environment. The Paramyxovididae family is divided to two sub-families, the Paramyxovirinae and the Pneumovirinae. It is within the Paramyxovirinae sub-family that morbilliviruses fall, along with respiroviruses, henipaviruses, rubulaviruses and avulaviruses. As well as canine distemper virus (CDV), the morbilliviruses include rinderpest, peste de petits ruminants, measles, phocine distemper and dolphin distemper.

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