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Basics ⬇

Basics

Definition

Acquired inflammatory response to virulent bacteria in lung parenchyma characterized by exudation of cells and fluid into conducting airways and alveolar spaces.

Pathophysiology

  • Bacteria-enter the lower respiratory tract primarily by inhalation or aspiration; less commonly by the hematogenous route. Infection incites an overt inflammatory reaction.
  • Tracheobronchial tree and carina-normally not sterile.
  • Oropharyngeal bacteria-frequently aspirated; may be present for an unknown time period in the normal tracheobronchial tree and lung; can cause or complicate respiratory infection; presence complicates interpretation of airway and lung cultures.
  • Respiratory infection-development depends on the complex interplay of many factors: inoculation site, number of organisms and their virulence, and age and resistance of the host.
  • Bacteria produce extracellular proteins called invasins that impair host defenses and assist in the spread of bacteria.
  • Viral infections-alter bacterial colonization patterns; increase bacterial adherence to respiratory epithelium; reduce mucociliary clearance and phagocytosis; thus allow resident bacteria to invade the lower respiratory tract.
  • Foreign body-inoculates bacteria into a focal lung region and leads to obstructive pneumonia.
  • Exudative phase-inflammatory hyperemia; extravasation of high-protein fluid into interstitial and alveolar spaces.
  • Leukocytic migration phase-leukocytes infiltrate the airways and alveoli; consolidation, ischemia, tissue necrosis, and atelectasis owing to bronchial occlusion, obstructive bronchiolitis, and impaired collateral ventilation.

Systems Affected

Respiratory-primary or secondary infection

Genetics

Heritable rhinitis/bronchopneumonia syndrome of Irish wolfhounds, unknown pathogenesis.

Incidence/Prevalence

Common in both young and old dogs, less common in cats.

Geographic Distribution

Widespread

Signalment

Species

Dog and cat

Breed Predilections

Dogs-sporting breeds, hounds, working breeds, and mixed breeds >12 kg

Mean Age and Range

Dogs-range, 1 month–15 years; many cases in dogs <1 year old

Predominant Sex

Dogs-60% males

Signs

Historical Findings

  • Cough
  • Labored breathing
  • Exercise intolerance
  • Anorexia and weight loss
  • Lethargy
  • Nasal discharge

Physical Examination Findings

  • Cough
  • Fever
  • Difficult or rapid breathing
  • Abnormal breath sounds on auscultation-increased intensity or bronchial breath sounds, crackles, and wheezes
  • Weight loss
  • Nasal discharge
  • Lethargy
  • Dehydration

Causes

Dogs

  • Most common primary respiratory pathogens-Bordetella bronchiseptica and Mycoplasma spp.
  • Most common gram-positive bacteria-Staphylococcus, Streptococcus, and Enterococcus spp.
  • Most common gram-negative bacteria-Escherichia coli, Klebsiella spp., Pseudomonas spp., Pasturella spp.
  • Anaerobic bacteria-found in pulmonary abscesses and various types of pneumonia (particularly with aspiration or foreign bodies); reported in ∼ 20% of cases.

Cats

  • Bacterial pathogens-poorly documented; B. bronchiseptica, Pasteurella spp., and Moraxella spp. most frequently reported. Mycoplasma spp. may be a primary pathogen in the lower respiratory tract.
  • Carrier state-may exist; periods of shedding B. bronchiseptica after stress; infected queens may not shed organism prepartum but begin shedding post-partum, serving as a source of infection for kittens.

Risk Factors

  • Preexisting viral infection.
  • Regurgitation, dysphagia, or vomiting.
  • Functional or anatomic defects-laryngeal paralysis, megaesophagus, cleft palate, primary ciliary dyskinesia.
  • Reduced level of consciousness-stupor, coma, and anesthesia.
  • Bronchial foreign body.
  • Bronchiectasis.
  • Immunosuppressive therapy-chemotherapy, glucocorticoids, immunosuppressives.
  • Severe metabolic disorders-uremia, diabetes mellitus, hyperadrenocorticism.
  • Sepsis.
  • Age-very young more susceptible to fatal infections.
  • Immunization status.
  • Environment-housing, sanitation, ventilation.
  • Phagocyte dysfunction-FeLV and diabetes mellitus.
  • Complement deficiency-rare.
  • Selective IgA deficiency-rare.
  • Combined T-cell and B-cell dysfunction-rare.

Diagnosis ⬆ ⬇

Diagnosis

Differential Diagnosis

  • Viral pneumonia-canine distemper virus, adenovirus, influenza virus, herpesvirus
  • Protozoal pneumonia-toxoplasmosis
  • Parasitic pneumonia-capillariasis, filaroidiasis
  • Fungal pneumonia-histoplasmosis, blastomycosis, coccidioidomycosis, and cryptococcosis
  • Eosinophilic pneumonia
  • Feline bronchial disease (asthma)
  • Pulmonary abscess
  • Pleural infection-pyothorax
  • Bronchial foreign body

CBC/Biochemistry/Urinalysis

Inflammatory leukogram-neutrophilic leukocytosis with or without a left shift; absence does not rule out the diagnosis.

Other Laboratory Tests

  • Arterial blood gas analysis-values correlate well with the degree of physiologic disruption; sensitive monitor of progress during treatment; PaO2 <80 mmHg on room air = mild or moderate hypoxemia; PaO2 <60 mmHg on room air = severe hypoxemia.
  • Consider serology for canine influenza virus.
  • Molecular diagnostics also available for viral and bacterial presence.

Imaging

Thoracic Radiography

  • Variable-diffuse, bronchointerstitial pattern to partial or complete alveolar infiltrates to consolidation.
  • Most common-alveolar pattern characterized by increased pulmonary densities (margins indistinct; air bronchograms or lobar consolidation).
  • More variable lung patterns in cats such as multifocal, patchy interstitial and alveolar changes and/or a diffuse nodular pattern.

Diagnostic Procedures

  • Microbiologic (aerobic, anaerobic bacterial, and mycoplasmal culture) and cytologic examinations for definitive diagnosis.
  • Samples-transtracheal or endotracheal washing, bronchoscopy, bronchoalveolar lavage (with or without bronchoscope), or fine-needle lung aspiration.
  • Degenerate neutrophils with septic inflammation (intracellular bacteria) predominating.
  • Recent antibiotic administration-non-septic inflammation likely.
  • Bacteria-not always obvious microscopically; always culture specimens, even if no bacteria are seen on cytology.

Pathologic Findings

  • Irregular consolidation in cranioventral regions.
  • Consolidated lung-varies from dark red to gray-pink to more gray, depending on age of patient and nature of the process.
  • Palpable firmness of the tissue.
  • Nidus of inflammation-bronchiolar-alveolar junction.
  • Early-bronchioles and adjacent alveoli filled with neutrophils and an admixture of cell debris, fibrin, and macrophages; necrotic to hyperplastic epithelium.
  • Later-neutrophilic, fibrinous, hemorrhagic, or necrotizing inflammation, depending on virulence of bacteria and host response.

Treatment ⬆ ⬇

Treatment

Appropriate Health Care

Inpatient-recommended with multisystemic signs (e.g., anorexia, high fever, weight loss, and lethargy).

Nursing Care

  • Maintain normal systemic hydration-important to aid mucociliary clearance and secretion mobilization; use a balanced multielectrolyte solution.
  • Saline nebulization-results in more rapid resolution if used with physical therapy and systemic antibacterials.
  • Physical therapy-chest wall coupage, tracheal manipulation to stimulate mild cough and postural drainage; may enhance clearance of secretions; always do immediately after nebulization; avoid allowing the patient to lie in one position for a prolonged time.
  • Oxygen therapy-as warranted for patients with hypoxemia, signs of respiratory distress.

Activity

Restrict during treatment (inpatient or outpatient), except as part of physical therapy after aerosolization.

Diet

  • Ensure normal intake with food high in protein and energy density.
  • Enteral or parenteral nutritional support-indicated in severely ill patients.
  • Use caution in feeding animals with megaesophagus, laryngeal dysfunction or surgery, pharyngeal disease, or recumbent patients.

Client Education

Warn client that high morbidity and mortality are associated with severe hypoxemia and sepsis.

Surgical Considerations

Surgery (lung lobectomy)-can be required with pulmonary abscessation or bronchopulmonary foreign body with secondary pneumonia; may be indicated if patient is unresponsive to conventional treatment and disease is limited to one or two lobes.

Medications ⬆ ⬇

Medications

Drug(s) Of Choice

Antimicrobials

  • Antimicrobials are best selected based on results of culture and susceptibility testing from tracheal wash or other pulmonary specimens.
  • Empiric antimicrobial therapy is justified when there is significant risk in obtaining adequate samples or if the time required to culture causes a life-threatening delay in treatment.
  • Reasonable initial antimicrobial choices pending culture results include amoxicillin-clavulanic acid (15 mg/kg PO q12h) or cephalexin (22–30 mg/kg PO q12h) with enrofloxacin (dogs, 5–10 mg/kg q12h or 10–20 mg/kg q24h; cats, maximum 5 mg/kg q24h), or trimethoprim-sulfonamide (15 mg/kg PO q12h).
  • Gram-positive cocci-ampicillin (22 mg/kg PO q12h), ampicillin-sulbactam; amoxicillin; amoxicillin-clavulanic acid; azithromycin; chloramphenicol, erythromycin; gentamicin; trimethoprimsulfonamide; first-generation cephalosporins.
  • Gram-negative rods-enrofloxacin, chloramphenicol; gentamicin; trimethoprim-sulfonamide; amikacin; marbofloxacin; carboxypenicillins.
  • Bordetella-doxycycline (5 mg/kg PO q12h); chloramphenicol; enrofloxacin; azithromycin.
  • Mycoplasma-doxycycline, enrofloxacin, marbofloxacin, chloramphenicol.
  • Anaerobes-amoxicillin-clavulanic acid; chloramphenicol; metronidazole; clindamycin; ticarcillin-clavulanic acid.
  • Antimicrobial nebulization for Bordetella-gentamicin nebulization 5 mg/kg q24h for 5–7 days, typically adjunctive with systemic antimicrobials.
  • Continue treatment for at least 10 days beyond clinical resolution and/or 1–2 weeks following radiographic resolution.

Contraindications

  • Anticholinergics and antihistamines-may thicken secretions and inhibit mucokinesis and exudate removal from airways.
  • Antitussives-potent, centrally acting agents inhibit mucokinesis and exudate removal from airways, can potentiate pulmonary infection and inflammation.

Possible Interactions

Avoid use of theophylline and fluoroquinolones concurrently.

Alternative Drug(s)

  • Expectorants-recommended by some clinicians; no objective evidence that they increase mucokinesis or mobilization of secretions.
  • Bronchodilators-recommended by some clinicians to alleviate bronchospasm.

Follow-Up ⬆ ⬇

Follow-Up

Patient Monitoring

  • Monitor respiratory rate and effort.
  • Complete blood count will normalize.
  • Arterial blood gases-most sensitive monitor of progress, pulse oximetry can be helpful.
  • Frequent thoracic auscultation.
  • Thoracic radiographs-improve more slowly than the clinical appearance.

Prevention/Avoidance

  • Vaccination-against upper respiratory viruses; against B. bronchiseptica if a dog is boarded or exposed to large numbers of other animals.
  • Catteries-environmental strategies to lower population density and improve hygiene help control outbreaks of bordetellosis.

Possible Complications

Sepsis can develop.

Expected Course and Prognosis

  • Prognosis-good with aggressive antibacterial and supportive therapy; more guarded in young animals, patients with immunodeficiency, and patients that are debilitated or have severe underlying disease.
  • Prolonged infection-potential for chronic bronchitis or bronchiectasis in any patient.
  • Mortality-associated with severe hypoxemia (low arterial oxygen concentration) and sepsis.

Miscellaneous ⬆

Miscellaneous

Associated Conditions

  • Frequently develops secondary to underlying functional or anatomic abnormalities-cleft palate; tracheal hypoplasia; primary ciliary dyskinesia; laryngeal paralysis; megaesophagus or other esophageal dysmotility disorder.
  • Bronchiectasis-both predisposing factor and potential complication.

Age-Related Factors

  • Young puppies and kittens-may have a poorer prognosis.
  • Underlying functional and anatomic problems and immunodeficiencies-suspect in young patients.

Pregnancy/Fertility/Breeding

Bitches or queens infected with B. bronchiseptica-may transmit infection to neonates.

Abbreviation

  • FeLV = feline leukemia virus

Author Melissa A. Herrera

Consulting Editor Lynelle R. Johnson

Acknowledgment The author and editors acknowledge the prior contribution of Phil Roudebush.

Client Education Handout Available Online

Suggested Reading

Dear JD. Bacterial pneumonia in dogs and cats. Vet Clin North Am Small Anim Prac 2014, 44(1):143–159.

Jameson PH, King LA, Lappin MR, et al. Comparison of clinical signs, diagnostic findings, organisms isolated, and clinical outcome in dogs with bacterial pneumonia: 93 cases (1986–1991). J Am Vet Med Assoc 1995, 206:206–209.