Canine Infectious Respiratory Disease Complex

Chapter 153

Canine Infectious Respiratory Disease Complex

Canine infectious respiratory disease is a widespread problem where large numbers of dogs are collectively housed indoors, as in shelters, commercial dog colonies, and breeding facilities. In shelter environments, canine infectious respiratory disease complex (CIRDC), also known as kennel cough or canine infectious tracheobronchitis, delays rehoming and may result in unmanageable costs related to treatment, quarantine, and isolation. CIRDC can develop in pet dogs after contact with large numbers of other dogs at dog parks, at canine sporting events such as fly ball, or during dog behavior classes. It also can occur after dogs (or their owners) visit veterinary hospitals, boarding facilities, or pet daycare centers.

With the widespread clinical application of molecular diagnostic assays, it has become increasingly apparent that the number of infectious agents that can damage the canine respiratory tract is much larger than previously recognized. Most cases are viral in origin. Viruses believed to play a role in canine contagious respiratory disease include canine herpesvirus (CHV), canine adenovirus type 2 (CAV-2), canine distemper virus (CDV), canine parainfluenza virus (CPiV), canine respiratory coronavirus (CRCoV), and canine influenza virus (CIV). CIV appears to have originated from an equine H3N8 influenza virus that first emerged in racing greyhounds in Florida and has spread across the United States through dog-to-dog transmission. CRCoV was first identified in a rehoming kennel in the United Kingdom and also appears to be widespread in the United States. It is distinct from canine enteric coronavirus. Finally, a pneumovirus (canine pneumovirus) also may be involved in CIRDC, but more research is required to determine the significance of this agent.

Coinfections with multiple viruses and bacteria such as Mycoplasma spp., Bordetella bronchiseptica, and Streptococcus equi subspecies zooepidemicus are common and contribute to an increased severity of disease. Studies in England have suggested that Mycoplasma cynos may be a primary pathogen (Rycroft et al, 2007), but whether this is true in other countries is unclear. Other Mycoplasma spp. may be more likely to represent normal flora that invade opportunistically. Although the majority of the canine respiratory pathogens have a worldwide distribution, their relative prevalence varies from year to year and among geographic locations. Even within a state or city, predominant pathogens may differ from one shelter and boarding kennel to another.

Mycoplasma spp. and the enveloped viruses CDV, CHV, CPiV, CRCoV, and CIV survive poorly in the environment and are susceptible to a variety of disinfectants. Despite this relative fragility, direct contact with organisms that persist even for a short time in the environment may be important for transmission in densely housed canine populations. CAV-2 is a nonenveloped virus and has the potential to survive several weeks on fomites. Other microorganisms that may persist in the environment and may be transmitted on fomites include B. bronchiseptica and S. equi subspecies zooepidemicus.

There are a large number of strains of B. bronchiseptica, varying in virulence and in host specificity. Nevertheless, strains that infect dogs can be passed to cats and vice versa. Shedding of B. bronchiseptica by both dogs and cats may continue intermittently for at least a month and sometimes several months after infection. Survival inside of phagocytes may allow for evasion of the immune system and help to explain persistent infections. S. equi subspecies zooepidemicus has been isolated from shelter dogs in outbreaks of severe pneumonia and may contribute to an increased severity of disease when present in coinfections with respiratory viruses. Both B. bronchiseptica and S. equi subspecies zooepidemicus have been uncommonly reported to infect humans. B. bronchiseptica has caused primary respiratory illness in immunocompromised people.


Generally it is not possible to identify the cause of transmissible respiratory disease in dogs based solely on clinical features. Each pathogen produces a similar spectrum of clinical signs. Occasionally, a specific causative diagnosis may be strongly suspected based on the presence of particular clinical signs, such as footpad hyperkeratosis or chorioretinitis in dogs with distemper, or dendritic corneal ulceration in dogs infected with CHV. However, the high prevalence of coinfections and increased severity of disease when multiple pathogens are present complicates diagnosis. In addition, other noncontagious causes of respiratory disease in dogs (such as inflammatory airway disease, respiratory tract neoplasia, or fungal pneumonia) can produce signs that resemble transmissible respiratory disease. A history of exposure to other dogs can increase suspicion for a diagnosis of CIRDC.

Most dogs experience self-limiting disease. Attempts to obtain a causative diagnosis should be made when disease persists for longer than 7 to 10 days or is complicated by secondary bacterial pneumonia. The latter may be accompanied by mucopurulent ocular or nasal discharge, fever, lethargy, and inappetence. When only one pet dog is affected, the diagnosis is further complicated by the fact that pathogens associated with CIRDC also can be isolated from healthy dogs. Thus the clinical significance of a positive test result for one of these pathogens may be unclear. When outbreaks occur in shelters or the pattern of endemic respiratory disease changes, attempts to make a causative diagnosis are indicated. Oropharyngeal, conjunctival, and nasal swabs or airway lavage specimens may be submitted for aerobic bacterial culture, for Mycoplasma culture, and for molecular diagnostic testing. In an outbreak situation, collection of multiple specimens from both affected and healthy dogs in the affected area facilitates diagnosis and interpretation of positive test results. Virus isolation also is available from some specialized veterinary diagnostic laboratories. Organism detection methods, such as polymerase chain reaction (PCR) assay or virus isolation, are best used early in the course of illness (e.g., the first 1 to 3 days) or in exposed dogs that have not yet developed clinical signs. Use of a combination of serologic and organism detection methods may also facilitate diagnosis when outbreaks occur. In shelter situations or in outbreaks in which severe disease occurs, necropsies can provide valuable information and should be performed by a veterinary pathologist as soon as possible after death or euthanasia. Tissues should be submitted for histopathologic analysis (in formalin), bacterial and viral cultures (fresh tissue), and PCR testing for respiratory viruses and bacteria (fresh or frozen tissue).

For dogs that develop chronic bronchitis or bronchopneumonia, a full physical examination, complete blood count, and thoracic radiographs are indicated, and if possible, specimens for aerobic bacterial culture and susceptibility testing, Mycoplasma culture, and molecular diagnostic testing should be collected using bronchoscopy and bronchoalveolar lavage. Tracheal lavage is acceptable if bronchoscopy is not possible or affordable; in some cases collection of an airway specimen may not be possible because of patient condition, and empiric antimicrobial drug therapy must be used.

< div class='tao-gold-member'>

Jul 18, 2016 | Posted by in PHARMACOLOGY, TOXICOLOGY & THERAPEUTICS | Comments Off on Canine Infectious Respiratory Disease Complex

Full access? Get Clinical Tree

Get Clinical Tree app for offline access