Definition and causes
Reagan and Sykes define CIRDC as a syndrome of acute-onset, contagious respiratory disease with a wide range of possible agents. They describe it as of particular concern in shelters, boarding facilities and day-care facilities [2]. They report that dogs become more likely to show signs the longer they stay in group housing [2]. The Merck Veterinary Manual states that dogs of any age can be affected and that puppies are more prone to severe disease [3].
The ISCAID guideline names the following implicated viruses [1]:
- canine adenovirus 2
- canine distemper virus
- canine respiratory coronavirus
- canine influenza viruses
- canine herpesvirus
- canine pneumovirus
- canine parainfluenza virus
Merck reports that co-infection with B. bronchiseptica, parainfluenza virus and adenovirus 2 is the most common combination. It adds that B. bronchiseptica may act as a primary pathogen, especially in dogs under 6 months old [3]. Merck also lists stress and extremes of ventilation, temperature and humidity as factors that appear to raise susceptibility and severity [3].
On Mycoplasma, Reagan and Sykes write that M. cynos is the only species significantly associated with canine respiratory disease, most often pneumonia. They add that whether it acts as a primary or secondary pathogen remains unclear, and that Mycoplasma spp. can be isolated from about 25% of healthy adult dogs [2]. They classify Streptococcus canis, Pasteurella, Pseudomonas, Staphylococcus, E. coli and Klebsiella pneumoniae as likely secondary opportunists rather than primary pathogens [2].
| Agent | Incubation (days) per Reagan and Sykes [2] | Vaccine availability per [2] |
|---|
| B. bronchiseptica | 2-6 | Parenteral inactivated; live intranasal, mucosal |
| Mycoplasma cynos | 3-10 | None available |
| Canine adenovirus 2 | 3-6 | Live parenteral and mucosal |
| Canine distemper virus | 3-6 | Live and recombinant; core |
| Canine herpesvirus-1 | 6-10 | None available |
| Canine influenza virus | 2-4 | Inactivated H3N2, H3N8, or both |
| Canine parainfluenza virus | 3-10 | Live parenteral and mucosal |
The same review's text gives a B. bronchiseptica incubation range of 2 to 10 days, wider than its table [2].
Clinical presentation
Merck describes the hallmark sign as a cough that sounds like a "goose honk," sometimes followed by retching or gagging [3]. The cough is easily induced by gentle palpation of the larynx or trachea [3]. Reagan and Sykes report that most dogs show a paroxysmal cough, serous eye discharge, nasal discharge or sneezing while keeping normal energy and appetite. In their account, fever, lethargy or reduced appetite points toward secondary bacterial infection [2]. Merck lists fever, purulent nasal discharge, depression, anorexia and a productive cough as signs of bronchopneumonia [3].
Two presentations carry particular weight in the sources.
- Distemper. ISCAID says distemper should always be considered in young dogs with mucopurulent eye and nasal discharge, even without other distemper signs [1]. Reagan and Sykes flag gastrointestinal signs, ocular discharge, neurologic signs or an unknown vaccination history as raising distemper risk [2].
- S. equi subsp. zooepidemicus. Reagan and Sykes describe mild early signs that can progress within 24 to 48 hours to severe hemorrhagic bronchopneumonia [2]. ISCAID advises suspecting this organism when acute hemorrhagic pneumonia or sudden death is reported [1].
Diagnosis and testing pitfalls
Merck advises suspecting kennel cough when the characteristic cough appears 5-10 days after exposure to other dogs. It calls thoracic radiographs "essential to determine the severity of disease and to exclude other causes of cough" [3]. Reagan and Sykes report that bloodwork is usually normal or mildly inflammatory. They add that radiographs are often normal or show an interstitial to bronchointerstitial pattern, with an alveolar pattern in more severe or secondary bacterial cases [2].
ISCAID notes that culture, Mycoplasma culture or PCR, and molecular respiratory panels are available. It cautions that:
- each organism can be found in healthy dogs;
- vaccine strains can be amplified;
- sensitivity may be limited because viral shedding peaks early [1].
For these reasons the panel generally does not recommend such tests for single dogs with typical signs, no evidence of pneumonia and no high-risk population involvement [1]. It also sees limited value in cytology of nasal discharge [1]. Reagan and Sykes recommend pursuing an etiologic diagnosis when signs are severe or rapidly progressive, last more than 7 to 10 days, or occur in an outbreak [2].
Reagan and Sykes list these pitfalls [2]:
- Upper airway cultures can grow normal flora.
- Low bacterial burden or prior antimicrobials can produce false-negative cultures.
- Live-attenuated vaccination within the previous few weeks can produce false-positive PCR results.
- Serology cannot distinguish vaccine response from infection.
In outbreaks, ISCAID describes a role for molecular assays, culture and viral serology. It advises testing samples from several affected dogs individually and performing necropsy when dogs die [1].
When pneumonia is suspected, the panel recommends a CBC and thoracic radiographs. If these support bacterial pneumonia, it recommends collecting a transtracheal, endotracheal or bronchoalveolar lavage specimen for cytology, culture, susceptibility testing and Mycoplasma culture [1]. It warns that unusual isolates such as Serratia or Stenotrophomonas from endoscopically collected samples may reflect scope contamination [1].
Severity categories used in treatment decisions
None of the cited sources defines a formal staging system for CIRDC. The table below summarizes how ISCAID recommendations differ by presentation [1].
| Presentation | ISCAID approach [1] |
|---|
| Cough or discharge, normal appetite and attitude | Observation; antimicrobials often not indicated |
| Mucopurulent discharge with fever, lethargy or inappetence, no pneumonia | Empirical doxycycline for 7-10 days |
| Mild pneumonia, shelter or boarding history, no systemic signs | Doxycycline described as a reasonable empirical choice |
| Pneumonia with signs of sepsis | Parenteral enrofloxacin or marbofloxacin plus a drug covering Gram-positive and anaerobic bacteria |
Treatment approaches
Uncomplicated disease
Reagan and Sykes describe supportive care for uncomplicated cases. They state that current guidelines recommend no specific therapy when signs have lasted under a week and the dog is bright and eating [2]. ISCAID states that most cases are thought to be viral and that antimicrobials are often not indicated [1].
Reagan and Sykes also report that:
- expectorants such as guaifenesin have not shown benefit;
- no antiviral therapy is recommended;
- cough suppressants can be considered for comfort [2].
They caution that narcotic antitussives such as hydrocodone are contraindicated with a productive cough because they can reduce bacterial clearance [2]. For persistent cough, Merck gives hydrocodone at 0.22 mg/kg, PO, every 6-12 hours or butorphanol at 0.5 mg/kg, PO, every 6-12 hours, and calls antitussives contraindicated in pneumonia [3].
Antimicrobial selection
ISCAID bases its doxycycline recommendation on good tolerance in dogs and on in vitro susceptibility of canine B. bronchiseptica isolates. It notes that those susceptibility studies used an unapproved standard [1]. Two reviewers dissented [1]:
- One argued that dogs without pneumonia and without high-risk factors need no antimicrobial at all.
- The other cited the absence of doxycycline breakpoint data for B. bronchiseptica or Mycoplasma in dogs.
The panel treats amoxicillin and amoxicillin-clavulanate as alternate first-line options if doxycycline fails or is not tolerated, a position 13 of 17 reviewers supported [1]. Dissenters raised unknown beta-lactam levels in bronchial secretions and the risk of selecting methicillin resistance [1]. Reagan and Sykes note growing antimicrobial resistance, especially among Bordetella isolates, which they cite as the reason culture-guided therapy is preferred [2].
| Drug | Dose as stated | Source |
|---|
| Doxycycline | 5 mg/kg, PO, q12h or 10 mg/kg, PO, q24h | ISCAID [1] |
| Amoxicillin | 22 mg/kg, PO, q12h | ISCAID [1] |
| Amoxicillin-clavulanate (dogs) | 11 mg/kg, PO, q12h | ISCAID [1] |
| Doxycycline or minocycline | 5-10 mg/kg, PO, every 12 hours for 7-14 days | Merck [3] |
| Amoxicillin/clavulanic acid | 12-25 mg/kg, PO, every 12 hours | Merck [3] |
| Trimethoprim-sulfa | 15-30 mg/kg, PO, every 12 hours, with Schirmer tear test before starting | Merck [3] |
| Enrofloxacin | 10 mg/kg, PO, every 24 hours | Merck [3] |
The sources differ on amoxicillin-clavulanate dosing.
They also differ on overall approach. Vieson and colleagues, in a Veterinary Medicine: Research and Reports review covering a much wider range of respiratory infections, describe antibiotics as the first therapeutic approach for infectious tracheobronchitis. They list amoxicillin/clavulanic acid, cephalexin, clindamycin and azithromycin [4]. That position diverges from the ISCAID observation-first approach [1].
The same review reports that aerosolized kanamycin or gentamicin reduced B. bronchiseptica numbers in the distal trachea and bronchi. This applied to severe bacterial infections that did not respond to parenteral antibiotics [4]. ISCAID does not recommend inhaled aminoglycosides, citing the absence of controlled safety or efficacy studies [1].
Pneumonia
ISCAID generally recommends parenteral antimicrobials for hospitalized pneumonia patients and, when sepsis is suspected, starting treatment within 1-2 hours [1]. For septic dogs, the panel pairs enrofloxacin or marbofloxacin with ampicillin or clindamycin pending culture [1]. It notes that canine S. equi subsp. zooepidemicus strains are susceptible to penicillin, amoxicillin and ampicillin, making amoxicillin-clavulanate unnecessary for that organism [1]. Reagan and Sykes write that pneumonia should prompt concern for underlying distemper or another immunosuppressive disease [2].
Monitoring, prognosis and client communication
ISCAID describes CIRDC as usually self-limited and does not recommend culture after successful treatment [1]. If the first drug fails and bacterial disease is still suspected after 7 days, the panel advises a more extensive workup before moving to fluoroquinolones or azithromycin [1]. For pneumonia, it notes that the common 4-6 week course lacks supporting evidence. It recommends re-evaluation no later than 10-14 days after starting treatment [1].
On prognosis, Merck reports that severity usually eases over the first 5 days but disease persists 10-20 days [3]. Reagan and Sykes note that B. bronchiseptica can be shed for at least a month [2].
Severe outcomes are concentrated in specific agents. Vieson and colleagues cite two examples [4]:
- S. equi subsp. zooepidemicus outbreaks with morbidity up to 100% and mortality of 50%-60%.
- 36% mortality in the first H3N8 influenza report in Florida greyhounds.
These figures describe outbreak reports, not typical household cases.
For client conversations, the sources support several points:
- Merck advises housing affected dogs apart from others [3].
- Reagan and Sykes note that cough can persist for weeks, and they recommend avoiding neck leads and barking triggers [2].
- ISCAID states that vaccinated dogs can still become colonized, shed organisms and show signs, though morbidity is generally lower than in unvaccinated dogs [1].
