Introduction

• Cause: canine distemper virus (CDV) Canine distemper virus.
• Still a problem in unvaccinated dogs, eg in inner city areas.
• Disease usually occurs in dogs less than 1 year of age.
• Signs: infection may be mild or generalized and severe.
• 50% of infections are subclinical/mild.
• Treatment: symptomatic - control through use of live attenuated vaccines.
• Prognosis: guarded, although animals may recover, disease often has residual effects.

Pathogenesis

Etiology

• Morbillivirus (Family Paramyxoviridae) Canine distemper virus.
• Large RNA virus (150-250 nm).
• Relatively labile; destroyed by heat, drying, detergents, solvents, disinfectants.
• Survives longer in cold (few weeks at just above freezing).
• Dogs, ferrets, mink and badgers; may also infect big cats.
• One antigenic type, though strains vary in virulence due to tissue tropism.

Predisposing factors

General

• Lack of vaccination.

• Close contact between dogs.

Specific

• Lack of vaccination.

Pathophysiology

• Infection via aerosol inhalation → primary replication in upper respiratory tract epithelium/tonsil → primary pyrexia → virus taken up by macrophages and lymphocytes → dissemination → leucopenia and lymphadenitis → secondary pyrexia.
• Outcome of infection depends on interaction of virus with lymphoid tissue:
  Either Some develop immunity → mild inappetence, pyrexia → recovery with a small percentage later → encephalitis.
  Or Some dogs → immunosuppression from viral replication in lymphoid tissue → secondary infections, eg Bordetella bronchiseptica Bordetella bronchiseptica , toxoplasmosis Toxoplasmosis , mycoplasmosis, coccidiosis Coccidiosis , viral enteritides Parvovirus disease associated with CPV-2.
• Transmission of virus in lymphocytes (varies with tissue tropism of virus strain):
  • Respiratory epithelium, lung macrophages.
  • Epithelium and lymphoid tissue of small intestine.
  • Neurones → demyelination, perivascular cuffing, gliosis.
  • Squamous epithelium of nares and footpads.
  • Transplacental infection of fetuses.

Timecourse

• Viremia within 2 days of infection.
• Epithelial damage in a few weeks.
• Incubation period 14-18 days for acute distemper.
• Virus in brain in 8-14 days, but signs several weeks later.
• Virus may persist in brain for months → delayed onset encephalitis.

Epidemiology

• Recovered animals have life-long immunity.
• Control by vaccination.
• Aerosol transmission → inhalation.
• Some puppies may be susceptible at 6 weeks old, due to early decline of maternal antibody.
• Virulence and tissue tropism varies between strains.
• Immunosuppression by CDV leads to secondary infection.

Diagnosis

Treatment

Prevention

Outcomes