Focus on Disease: Canine infectious respiratory disease complex and bordetella bronchiseptica
Dr Jenny Stavisky MRCVS BVM&S PhD PGCHE FHEA
Published October 2019
Bordetella bronchiseptica is a Gram negative, aerobic coccobacillus. It forms part of the ‘kennel cough’ or canine infectious respiratory disease complex (CIRDc), the names given to commonly seen signs of upper respiratory tract infections in dogs. Despite its name, the syndrome is not confined to kennels and may be transmitted anywhere where dogs mix, including shows, training classes, parks and veterinary surgeries. The pathogenesis of CIRDc is thought to frequently involve initial infection with an upper respiratory tract pathogen such as canine respiratory coronavirus or canine parainfluenza virus (CPiV). This then facilitates secondary infection, often with opportunistic organisms already present in the respiratory tract, such as Mycoplasma cynos. B bronchiseptica may play the role of either primary pathogen or secondary invader.
B bronchiseptica is a rare but potentially serious zoonosis. Case reports of infections in cystic fibrosis and transplant patients have documented serious sequelae and even death. Zoonotic transmission following vaccination (including the administrator, handler and owner) is thought to be possible but extremely rare. Postvaccination shedding may occur for several weeks.
Where immunocompromised humans are in contact with dogs, the low but predictable risk of vaccination must be carefully weighed against the less predictable risk of clinical infection. Appropriate advice, including recommending at-risk owners contact their medical practitioner, should be offered.
Transmission between dogs and cats has been suggested to occur. Additionally, cats have also been implicated in zoonotic infections. In some parts of world, canine influenza viruses also contribute; these are not yet thought to be regularly circulating in the UK.
Pathogenesis and clinical signs
A hacking cough is clinically typical of CIRDc, although not pathognomonic of any one pathogen. Differentials include retching, regurgitation and oropharyngeal foreign body. In addition to the cough, dogs may have submandibular lymph node enlargement and mild pyrexia. While affected animals typically remain bright and well, in severe cases or particularly susceptible individuals, bronchopneumonia can occur, with associated increased respiratory effort, pyrexia and lethargy. Deaths are relatively uncommon.
Where outbreaks of severe disease occur, aspects of husbandry such as ventilation, stress and biosecurity should be assessed and alternative pathogens such as Streptococcus equi zooepidemicus considered.
Diagnosis of CIRDc is usually made in the presence of characteristic clinical signs. Diagnostic testing is indicated in the presence of an outbreak, where the results could inform a change in policy (such as therapy or vaccination), or in individual cases where signs are severe or fail to resolve.
For upper respiratory tract disease, a deep oropharyngeal swab should be taken. A number of PCR panel tests are available, and can be helpful in checking for the presence of several organisms simultaneously. Diagnostic results need to be interpreted with care since some of the components of CIRDc can be part of normal respiratory tract flora. Additionally, CIRDc may involve different pathogens at different stages of infection. Therefore, in an outbreak, sampling several dogs at different stages of infection may be helpful.
Treatment and prevention
For most dogs with CIRDc, specific antibiotic therapy is not necessary, with symptomatic treatment (avoiding pulling on collars, rest and NSAIDs if needed) being sufficient. The use of antitussives is contentious. International Society for Companion Animal Infectious Diseases guidelines suggest empirical use of antibiotics where there is a mucopurulent discharge alongside signs of lethargy, pyrexia or anorexia. BSAVA PROTECT ME suggests that antibiotics are only indicated if clinical signs persist for more than 10 days and/or the dog is systemically unwell. Where necessary, both guidelines suggest doxycycline or potentiated amoxicillin as the first choice antibiotics. Where cases fail to resolve, or if the lower respiratory tract is involved, culture and sensitivity testing and further investigations such as bronchoalveolar lavage may be indicated.
Several pathogens involved in CIRDc are part of canine core vaccines. In the UK, Bordetella vaccination is given intranasally, often combined with CPiV; elsewhere, subcutaneous and oral vaccines exist. Mucosal immunity commences within three days. As the vaccine is live, some dogs may have a transient cough for several days afterwards. It is essential to note that vaccination will not fully prevent clinical CIRDc due to the range of pathogens that contribute to this syndrome.
Following natural infection, dogs may shed Bordetella at diminishing levels for up to 12 weeks, with transmission mainly via aerosol. Restricting social mixing of dogs recovering from CIRDc is therefore important in limiting spread.
Read our surveillance report with a focus on CIRD here.
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