Canine influenza virus
The canine influenza virus replicates in the epithelial tissue lining the nasal passages, trachea, bronchi, and bronchioles.
Viral replication results in epithelial cell necrosis and exposure of the basement membrane, which predisposes to secondary bacterial infection, which commonly progresses to pneumonia.
Spread is by aerosol and foment transfer, and has emerged transcontinentally due to the high frequency of transport of dogs across state borders for transnational dog shows and stud programs.
Strains which have been reported as pathogenic to dogs include:
- H5N2 - mild upper respiratory signs only
- H3N8 - common in shelter dogs
- H3N2 - transmissible to cats
Recent outbreaks of H3N8 have been recorded in the greyhound, which quickly spread across the United States to domestic dogs. Affected dogs died rapidly from hemorrhagic pneumonia and the etiological agent was isolated on postmortem.
Serologic evidence indicates that there is a sustained horizontal transmission of canine influenza H3N8 virus between dogs in the United States and the United Kingdom. Seroprevalence is higher in shelter dogs and those vaccinated rather than unvaccinated
Naïve dogs are susceptible and high morbidity rates (60-80%) are expected. The onset of clinical signs is typically less than 5 days after infection. Peak viral shedding occurs 2 - 4 days after infection, meaning that dogs may be at their most infectious prior to showing signs of disease.
Affected dogs are have symptoms of lethargy, anorexia, low grade fever, serous/mucoid/mucopurulent nasal discharge and rhinitis.
The most common sign is a persistent dry cough that lasts for several weeks, despite treatment. After the first week of coughing, 10 - 20% of dogs progress to more severe signs, including fever, dyspnea and secondary pneumonia.
Diagnosis is based on presenting clinical signs and isolation of virus using PCR assays from nasal swabs.
Cultures have revealed a variety of bacteria including Staphylococcus spp, hemolytic and nonhemolytic Streptococcus spp, Pasteurella multocida, Klebsiella pneumoniae, Escherichia coli, and Mycoplasma spp.
A canine influenza vaccine is available in the United States made from inactivated virus.
The vaccine has been shown to reduce the incidence and severity of lung lesions, as well as the duration of coughing and viral shedding, and is administered by subcutaneous injection in two doses, two to four weeks apart.
- Shelter Medicine
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