Introduction

• Cause: bacterial infection, may be primary but often secondary to underlying pulmonary disease.
• Signs: cough, lethargy, exercise intolerance, dyspnea, +/- fever.
• Diagnosis: signs, radiography, cytology.
• Treatment: antibiotics, physical therapy, supportive care.
• Prognosis: good to guarded.

Pathogenesis

Etiology

• Primary respiratory tract pathogens: bacteria:
  • Bordetella bronchiseptica Bordetella bronchiseptica.
  • Streptococcus equi subspecies zooepidemicus Streptococcus equi.
• Secondary to other pulmonary infections:
  • Viral pneumonia.
  • Fungal pneumonia.
  • Parasitic pneumonia Eosinophilic bronchitis/pneumonia , eg:
    • Filaroides milksi Filaroides milksi or F. hirthi Filaroides hirthi.
    • Dirofilaria immitis Dirofilaria immitis.
• Secondary to physical pulmonary damage:
  • Aspiration of GI tract contents.
  • Smoke inhalation Smoke inhalation.
  • Inhaled foreign bodies Airway foreign body.
  • Secondary to chronic airway or lung disease:
    • Chronic bronchitis Chronic bronchitis.
    • Bronchiectasis Lung: bronchiectasis.
    • Pulmonary fibrosis Idiopathic pulmonary fibrosis.
    • Tracheal collapse Trachea: collapse.
    • Laryngeal paralysis Larynx: paralysis.
    • Brachcephalic airway syndrome Brachycephalic airway obstruction syndrome.
• Systemic blood-borne infection (hematogenous pneumonia; rare).
• Reduced immunity, eg ciliary dyskinesia Primary ciliary dyskinesia.

Predisposing factors

General

• Unvaccinated (increased risk of infections, ie primary bacterial respiratory pathogens, viral or parasitic disease).
• Management, eg boarding kennel, shelter animal.
• Any vomiting or regurgitation (risk for aspiration).
• Anesthesia or heavy sedation (atelectasis Lung: atelectasis , risk for aspiration Lung: aspiration pneumonia ).

• Debility or malnutrition.
• Age (young and old are at increased risk of severe disease).
• Conformational abnormalities, eg brachycephalic conformation.
• Hunting dogs (increased risk of inhaled foreign bodies because nose on ground while panting with mouth wide open).
• Certain breed predisposition to inherited deficiencies in pulmonary defences, eg Bichon Frise Bichon Frise or Newfoundland Newfoundland for primary ciliary dyskinesia Primary ciliary dyskinesia.

Pathophysiology

• Bacteria normally present colonizing pharynx and airways can invade and proliferate if there is:
  • Inflammation:
    • Chronic, eg chronic bronchitis.
    • Acute, eg viral infection, aspiration of GI contents.
  • Epithelial denudation, eg aspiration of GI contents.
  • Ciliary escalator dysfunction:
    • Ciliary dyskinesia.
    • Bronchiectasis acquired or congenital.
    • Bordetella bronchiseptica infection.
  • Atelectasis, ie bacterial trapping in collapsed alveoli.
  • Decreased ability to cough, eg pain, physical weakness.
  • Inherent immunosuppression, eg very young or old age, drug therapy.
  • Foreign body nidus.
• Hematogenous pneumonia may occur if septic emboli are present due to:
  • Sepsis.
  • Bacterial endocarditis Endocarditis: bacterial.
• In dogs, secondary bacterial pneumonia is usually caused by gram negative aerobic pathogens such as E. coli Escherichia coli , Pseudomonas spp Pseudomonas , or Klebsiella Klebsiella pneumoniae. In a minority of cases, gram positive cocci such as Staphylococci Staphylococcus spp may occur.

Timecourse

• Variable. Acute onset over days or chronic over months even years.
• May be superimposed on chronic disease.

Diagnosis

Treatment

Outcomes