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Bordetella bronchiseptica

Dr Jenny Stavisky explores the clinical signs, diagnosis, treatment and prevention of a Gram negative, aerobic coccobacillus, that forms part of the "kennel cough" or canine infectious respiratory disease complex (CIRDc). These are 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 and Bordetella bronchiseptica, playing the role of either primary pathogen or secondary invader.

Bordetella 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, although 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 subspecies zooepidemicus considered.

Diagnosis

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 polymerase chain reaction (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 non-steroidal anti-inflammatory drugs (NSAIDs) if needed) being sufficient. The use of antitussives is contentious.

The 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. The British Small Animal Veterinary Association's PROTECT ME guidance 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.

References

  • Garcia-de-la-Fuente C, Guzman L, Cano M, et al. Microbiological and clinical aspects of respiratory infections associated with Bordetella bronchiseptica. Diagnostic Microbiology and Infectious Disease 2015;82:20–5
  • Brady C, Ackerman P, Johnson M, McNamara J. Bordetella bronchiseptica in a pediatric cystic fibrosis center. Journal of Cystic Fibrosis 2014;13:43–8
  • Ner Z, Ross LA, Horn MV, et al. Bordetella bronchiseptica infection in pediatric lung transplant recipients. Pediatric Transplantation 2003;7:413–7
  • Gisel JJ, Brumble LM, Johnson MM. Bordetella bronchiseptica pneumonia in a kidney-pancreas transplant patient after exposure to recently vaccinated dogs. Transplant Infectious Disease 2010;12:73–6
  • Lemura R, Tsukatani R, Micallef MJ, Taneno A. Simultaneous analysis of the nasal shedding kinetics of field and vaccine strains of Bordetella bronchiseptica. Veterinary Record 2009;165:747–51
  • Binns SH, Dawson S, Speakman AJ, et al. Prevalence and risk factors for feline Bordetella bronchiseptica infection. Veterinary Record 1999;144:575–80
  • Register KB, Sukumar N, Palavecino EL, et al. Bordetella bronchiseptica in a paediatric cystic fibrosis patient: possible transmission from a household cat. Zoonoses and Public Health 2012;59:246–50.