Canine infectious respiratory disease (CIRD) is a complex, multi-factorial disease process of dogs. Previously named infectious tracheobronchitis (or more commonly, kennel cough), this disease is composed of numerous viral, bacterial and mycoplasmal organisms. In most cases more than one of these organisms is implicated in the infection.
The main viruses involved in CIRD include Canine Adenovirus Type 2 CAV-2), Canine Parainfluenza Virus (CPIV), Canine Influenza Virus (CIV), Canine Respiratory Coronavirus (CRCoV), Canine Distemper Virus (CDV), and Canine Herpesvirus (CH). The main bacterium involved is Bordetella bronchiseptica; however, Streptococcus equi subsp zooepidemicus has been implicated in a severe hemorrhagic pneumonia which may contribute to the disease complex. A mycoplasmal species (M.cynos) may be involved as well.
The purpose of today’s blog is to talk a bit more about CRCoV, one of the newer viruses implicated in the CIRD complex. This virus is genetically different from the canine enteric coronavirus that most practitioners may be more familiar with. In fact, this divergent strain is most similar genetically to bovine coronavirus. This virus was discovered in 2003 and is typically associated with more mild cases of CIRD and occurs during the early stages of the disease. Early infection with CRCoV may predispose dogs to other viral or bacterial pathogens, thus protentiating more serious respiratory disease. CRCoV has tropism for the upper respiratory tissues including the nares and trachea; however, infection can also be established in the lower airways. It has also been positively identified in rectal swabs but its role in enteric disease is unknown. CRCoV has been shown to be present in Europe, North America and Asia.
There is no specific treatment for CRCoV and spontaneous resolution is common. Most healthy dogs recover within 2 weeks without medical intervention. Co-infection with a number of other viruses and bacteria is common. For uncomplicated cases, antibiotics are generally not indicated, but for more severe cases (fever, lethargy, dyspnea, or progression of disease despite rest) antibiotics may be indicated to combat secondary bacterial pathogens. If bronchopneumonia, interstitial pneumonia or sepsis is suspected, IV antibiotics and hospitalization are indicated.
Dogs that are housed in shelters, kennels or high density housing situations are at a greater risk. Other risk factors include immunocompromise and stress. Seasonality may play a role, as many infections are diagnosed in the fall and winter when outdoor temperatures are cooler. Age may also play a role with CRCoV infection, with dogs that are less than a year of age generally being seronegative for the virus, and dogs 1-9 years of age having an increased seroprevalence.
Supportive care is the best approach to CIRD and may include:
Hospitalization and fluid therapy: For animals with severe respiratory compromise, hospitalization may be required. In general, hospitalization is avoided due to the highly contagious nature of CIRD. If the animal is severely dyspneic, oxygen therapy is indicated, which must be delivered in a hospital setting. Many of these severely affected animals will be dehydrated and additionally require IV fluid therapy.
Antitussives: The evidence to support the use of antitussives for CIRD is lacking despite their regular use. Over the counter products are likely ineffective. Hydrocodone and butorphanol may provide some relief, but the risks of respiratory depression and reduced clearance of bacteria (secondary to decreased expectoration) need to be weighed against the benefits. In general, antitussives are not recommended for coughs due to an infectious cause unless quality of life issues are a concern.
Bronchodilators: are again often reported in the literature, but there is little to evidence of their effectiveness for CIRD.
Glucocorticoids: have also been used for reducing inflammation associated with cough. The use of these drugs is controversial as they can exacerbate disease, and the evidence to support their use is lacking.
Nebulizers: For dogs with excessive tracheal and bronchial secretions, aerosol therapy may be beneficial. Aerosols may help loosen respiratory secretions to facilitate expectoration. Aerosols can be composed of steam or saline, or can contain NSAIDs or antibiotics.
Contraindications: There are no studies that support the administration of intranasal vaccination in the face of infectious respiratory disease in the canine patient. Administering intranasal vaccinations to clinically ill patients is generally not recommended. Additionally, there are no approved or effective anti-viral products for the use in dogs with CIRD. Expectorant therapies (mucolytics) are also not recommended for routine use in CIRD patients as they have not been shown to be of benefit.
No vaccine is currently available for CRCoV and there is likely no cross protection from enteric canine coronavirus vaccines. This virus may be one of the reasons that traditional vaccines against kennel cough (which confer partial protection against CAV-2, CPIV, and Bordetella) are failing to work in certain situations.
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