Etiology

• Causative Agent: Canine distemper virus (CDV), a paramyxovirus closely related to measles and rinderpest viruses.

• Virus Characteristics: Fragile, enveloped, single-stranded RNA virus; unstable outside the host.

• Transmission: Primarily via aerosol droplets from infected animals; dogs may shed the virus for several months.

• Viral Replication: Begins in lymphatic tissues of the respiratory tract, followed by viremia and spread to multiple tissues, including respiratory, gastrointestinal (GI), urogenital, CNS, and optic nerves.

• Epidemiology: Affects a wide range of species including Canidae, Mustelidae, Procyonidae, some Felidae, primates, and even elephants. Domestic dogs are the main reservoir species.

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Clinical Signs

• Diphasic Fever: Initial fever at 3-6 days post-infection, followed by a second fever.

• Respiratory Symptoms:

  • Serous nasal discharge, mucopurulent ocular discharge.

  • Pneumonia, often secondary bacterial infections.

• Gastrointestinal Symptoms:

  • Diarrhea, anorexia.

• Neurological Complications:

  • Myoclonus, seizures (chewing-gum seizures), tremors.

  • Circling, head tilt, nystagmus, paresis to paralysis.

  • Possible chronic progressive neurological disease (Old Dog Encephalitis - ODE).

• Dermatologic Findings:

  • Hyperkeratosis of footpads and nose.

  • Pustular dermatitis (rare).

  • Enamel hypoplasia in young dogs.

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Diagnosis

• Clinical Evaluation: Based on multisystemic signs (respiratory, GI, neurological).

• Laboratory Confirmation:

  • Reverse transcriptase PCR (RT-PCR) and antibody detection tests (ELISA, immunofluorescence assay [IFA]).

  • Diagnostic samples: conjunctival smears, blood, transtracheal wash, urine, bone marrow aspirates.

  • Histology and IFA for postmortem diagnosis; viral inclusion bodies in tissues like lymphatic, respiratory, and GI epithelium.

• Differential Diagnosis:

  • Parvovirus infection, infectious canine tracheobronchitis, infectious canine hepatitis.

  • Intoxications (e.g., lead or organophosphates).

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Treatment & Prognosis

• Supportive Care: Mainstay of treatment; includes:

  • Hydration, nutrition, and management of secondary bacterial infections.

  • Antipyretics, analgesics, anticonvulsants.

  • Anticonvulsant treatment for seizures.

• Experimental Therapies:

  • Xenogeneic anti-CDV antibodies show promise in improving survival rates in puppies.

  • Botulinum toxin injections may alleviate severe myoclonus.

• Neurological Prognosis:

  • Neurological signs may be progressive and difficult to treat.

  • Some dogs recover fully from multisystemic signs but may experience persistent neurological deficits.

  • Glucocorticoids may help in chronic progressive neurological disease.

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Prevention

• Vaccination:

  • Core vaccination for puppies with modified live virus (MLV) distemper vaccine starting at 6 weeks, followed by booster doses every 3-4 weeks until 16 weeks of age.

  • Use of MLV measles vaccine may be an alternative in the presence of maternal antibodies.

• Revaccination:

  • Annual vaccination is standard but may be extended to every 3 years based on evidence of long-term immunity.

  • Extra-label use of vaccines (e.g., recombinant vaccines) may be used for exotic or at-risk species.

• Environmental Control:

  • Canine distemper virus is sensitive to lipid solvents and disinfectants (e.g., phenols, quaternary ammonium compounds).

  • Regular cleaning and disinfection of animal care facilities are essential to prevent transmission.

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