Canine Pneumonia: Identifying Aspiration, Bacterial and Secondary Causes

Bacterial pneumonia remains a frequent clinical diagnosis in dogs with acute or chronic respiratory disease. Recognizing how pneumonia develops can help the veterinarian identify an underlying problem that may need attention alongside the pulmonary infection. 

Bacterial pneumonia involves colonization of the airways or pulmonary parenchyma by bacteria, resulting in exudation and lung consolidation. 

Identify the Potential Cause 

Common causes of bacterial pneumonia include aspiration of gastrointestinal tract contents, decreased ciliary function, and infection with opportunistic pathogens secondary to immunosuppression^1,2. 

Bacteria associated with respiratory infections in dogs include Bordetella bronchiseptica, Escherichia coli, Klebsiella, Streptococcus, Staphylococcus, Pasteurella, Proteus and Pseudomonas species^2,3,4,5,6. 

The presence of pneumonia should therefore prompt consideration of the mechanism that allowed bacterial colonization rather than focusing exclusively on the pulmonary lesion. 

Aspiration Pneumonia Requires Particular Attention 

Aspiration pneumonia is a potentially life-threatening inflammatory pulmonary condition associated with esophageal disease, prolonged anesthesia, seizures, refractory vomiting, and laryngeal dysfunction^7,8. 

Aspiration-related pulmonary damage can result in ventilation-perfusion mismatch and hypoxemia. This makes assessment of oxygenation particularly relevant in clinically affected dogs. Hypoxemia was recorded in more than 75% of dogs with aspiration pneumonia, while PaO₂ values between 69 and 77 mmHg have also been reported¹. 

Consider Previous Respiratory Infection² 

Community-acquired pneumonia may occur following viral colonization and infection of the upper respiratory tract. Canine respiratory coronavirus, pneumovirus, herpesvirus, and parainfluenza virus are described in dogs living in overcrowded or stressful environments. 

These infections are mostly acute and self-limiting, but they can affect host immune defences and predispose dogs to bacterial respiratory infections. 

Recurrent Pneumonia May Signal a Foreign Body² 

Inhaled foreign bodies such as grass awns or plastic material can carry mixed bacterial and fungal populations into the lungs. Organisms described include Streptococcus, Pasteurella, Nocardia, Actinomyces, and anaerobic bacteria. 

A useful clinical clue is recurrence after treatment. Focal pneumonias associated with foreign material may initially respond to antimicrobial therapy but relapse shortly after therapy is discontinued. Foreign material commonly remains at the carina or enters the caudodorsal principal bronchi . 

Practical Clinical Insight 

Thoracic radiography can support evaluation of pulmonary disease, while bronchoscopy may assist in identifying airway abnormalities and foreign material. Transthoracic FNAC is also described as a direct approach for non-resolving pneumonias. 

When pneumonia does not resolve as expected, the possibility of an underlying cause such as aspiration or retained foreign material deserves renewed consideration. 

References 

1. Dear JD. Bacterial pneumonia in dogs and cats: an update. The Veterinary Clinics of North America. Small Animal Practice. 2019 Dec 5;50(2):447. https://pmc.ncbi.nlm.nih.gov/articles/PMC7114575/pdf/main.pdf 

2. Kaur J, Singh S. Respiratory diseases and their diagnosis in dogs: A review. Indian Journal of Animal Research. 2022. https://arccjournals.com/journal/indian-journal-of-animal-research/B-4994 

3. Attili A, Cerquetella M, Pampurini F, Laus F, Spaterna A, Cuteri V. Association between enrofloxacin and N-acetylcysteine in recurrent bronchopneumopathies in dogs caused by biofilm producer bacteria. Journal of Animal and Veterinary Advances. 2012;11(4):462-9. https://pubblicazioni.unicam.it/bitstream/11581/227268/1/Enrofloxacin_NAC_JAVA_2012.pdf 

4. Johnson LR, Queen EV, Vernau W, Sykes JE, Byrne BA. Microbiologic and cytologic assessment of bronchoalveolar lavage fluid from dogs with lower respiratory tract infection: 105 cases (2001–2011). Journal of Veterinary Internal Medicine. 2013 Mar;27(2):259-67. https://onlinelibrary.wiley.com/doi/pdf/10.1111/jvim.12037https://onlinelibrary.wiley.com/doi/pdf/10.1111/jvim.12037 

5. Taha-Abdelaziz K, Bassel LL, Harness ML, Clark ME, Register KB, Caswell JL. Cilia-associated bacteria in fatal Bordetella bronchiseptica pneumonia of dogs and cats. Journal of Veterinary Diagnostic Investigation. 2016 Jul;28(4):369-76. https://journals.sagepub.com/doi/pdf/10.1177/1040638716646806 

6. Bajtoš M, Kožár M. The use of endoscopic diagnosis in dogs with upper respiratory diseases with respect to the localisation of pathogens and the subsequent therapy. Folia Veterinaria. 2021 May 13;65(1):75-83. https://reference-global.com/download/article/10.2478/fv-2021-0010.pdf 

7. Tart KM, Babski DM, Lee JA. Potential risks, prognostic indicators, and diagnostic and treatment modalities affecting survival in dogs with presumptive aspiration pneumonia: 125 cases (2005–2008). Journal of Veterinary Emergency and Critical Care. 2010 Jun;20(3):319-29. https://www.researchgate.net/profile/Kelly-Tart/publication/45269440 

8. Proulx A, Hume DZ, Drobatz KJ, Reineke EL. In vitro bacterial isolate susceptibility to empirically selected antimicrobials in 111 dogs with bacterial pneumonia. Journal of Veterinary Emergency and Critical Care. 2014 Mar;24(2):194-200. https://www.academia.edu/download/109091207/Pneumonia_20bacterial_20isolate_20susceptibility.pdf