Canine Distemper Virus

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Canine distemper virus

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Large single-stranded RNA virus of Morbillivirus genus

Surrounded by lipoprotein envelope composed of viral glycoproteins

Different strains; neurotropic, pneumotropic, or epidermal tissues

Virulence mostly determined by viral glycoproteins

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Animals affected by CDV

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Foxes, ferrets, badgers, mink, wolves, seals, dolphins

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Most commonly spread by...

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Aerosol or droplet exposure

Urine and faeces

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Labile?

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Very labile - heat/drying/UV light

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Susceptible to disinfectants?

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Yes as is enveloped virus - benzalkylonium and glutaraldehyde (formula H) or tertiary amines (trigene)

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Pathogenesis

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CDV multiplies in macrophages and migrates via lymphatics to tonsils and bronchial lymph nodes

Widespread virus replication within lymphoid tissues -> pyrexia and leukopenia within 4-6 days of infection

8-10 days - CDV migrates haematogenously to epithelium and CNS cells

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What results in shedding?

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Presence of virus within epithelial cells, even in subclinical cases

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Clinical outcome depends on

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Level of CDV antibody titres and cell-mediated immunity

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Individuals with adequate CDV antibody titres and cell-mediated immunity

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Virus cleared from most cells and usually no clinical signs

Can still shed virus

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Intermediate CMI and delayed antibody response:

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Infection of epithelial tissues and clinical signs

High virulence strains or high dose may result in severe morbidity

Recovery associated with long-term immunity and cessation of viral shedding

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Poor immune status

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Severe disease and virus persists until death usually

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Vaccinated dogs

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may also show clinical signs

CNS infection may occur in presence or absence of adequate immunity

Adequately immune - acute CNS signs unlikely but may still get chronic encephalitis

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Resp. clinical signs

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Bilateral serous to muco-purulent oculo-nasal discharge

Concurrent coughing and dyspnoea if bacterial secondary infection

Mildly-affected cases need to be differentiated from kennel cough

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Ocular CS

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Bilateral serous to muco-purulent conjunctivitis

Keratoconjunctivitis sicca

Mild anterior uveitis

Necrosis/degeneration of retina

Optic neuritis with neurological involvement

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GI CS

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Damage to epithelium -> vomiting and diarrhoea

Anorexia, dehydration and weight loss

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Dermatological CS

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Pustular dermatitis

Nasal and digital hyperkeratosis

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Neurological CS

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Seizures, vestibular disease, ataxia or myoclonus

Acute meningioencephalitis if direct damage to CNS with other systemic signs

Old dog encephalitis - chronic relapsing neurological signs may recur after many years with absence of infection

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Dental CS

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Infection before eruption of permanent dentition -> damage to enamel and dentine -> distemper rings

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transplacental infection

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Abortion and stillbirth or persistent excretory of virus, depending on stage of gestation

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Diagnosis

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Presumptive diagnosis in unvaccinated dogs esp. 3-6 months of age with clinical signs -

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subclinica, cases

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50-70% of cases

may be CDV in transient upper respiratory infections

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Lab abnormalities

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Absolute lymphopenia

Non-specific biochemical changes related to dehydration and/or polyclonal gammopathy

Distemper inclusions on peripheral blood smears - false negatives common

CSF may show increased protein and increased cell count esp. mononuclear

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Immunocytology

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Immunofluorescent antibody (IFA) on conjunctival smears, tonsillar tissue, leukocytes or respiratory epithelium is helpful in acute phase of disease

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Serology

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ELISA for anti-CDV IgG and IgM. May confirm infection, may be difficult in vaccinated animals

In dogs with neurological signs there may be anti-CDV antibody in CSF

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PCR

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CSF, respiratory secretions

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Treatment

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Anti-emetics

Coupage and nebulisation if bronchopneumonia present

Antibiotics if secondary infection present

IVFT

Anticonvulsants for seizures