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Basics ⬇

Outline

BASICS

Overview!!navigator!!

The development of an inflammatory response in the lung parenchyma to bacterial pathogens, with extension to the pleural space and subsequent pleural effusion.

Signalment!!navigator!!

  • No breed or sex predilection
  • All ages but rare in foals

Signs!!navigator!!

  • Acute—fever, lethargy, anorexia, tachypnea, decreased bronchovesicular sounds ventrally, radiating heart sounds, pleural friction rubs, nasal discharge, pleurodynia, soft cough, ventral or limb edema
  • Subacute or chronic—fever (may be intermittent), weight loss, exercise intolerance, ventral or limb edema, intermittent colic, tachypnea relative to the volume of pleural effusion

Causes and Risk Factors!!navigator!!

  • Mixed infections are common. Streptococcus equi ssp. zooepidemicus is the primary Gram-positive pathogen. Escherichia coli, Klebsiella pneumoniae, Actinobacillus spp., and Pasteurella spp. are the most common Gram-negative pathogens. Anaerobic bacteria are isolated in about one-third of cases. Mycoplasma has been isolated in rare cases
  • The most significant risk factor is long-distance transport. Also, aspiration pneumonia, thoracic trauma strenuous exercise, exposure to dust or gases, exercise-induced pulmonary hemorrhage, viral disease, general anesthesia, immunodeficiency, immunosuppressive drugs, and malnutrition

Diagnosis ⬆ ⬇

Outline

DIAGNOSIS

Differential Diagnosis!!navigator!!

Pneumonia, neoplasia, hemothorax, cardiac disease, equine infectious anemia, diaphragmatic hernia.

CBC/Biochemistry/Urinalysis!!navigator!!

  • Neutrophilic leukocytosis and hyperfibrinogenemia. Neutropenia can be present in acute cases
  • Monocytosis, anemia, and hypergammaglobulinemia (subacute or chronic)

Imaging!!navigator!!

  • Thoracic US—fluid between the thoracic wall and the lung parenchyma. Fluid may be loculated if there is significant fibrin deposition. Pulmonary consolidation or atelectasis, and pulmonary abscesses (if superficial) can be detected. Small hyperechoic images are suggestive of anaerobic infection
  • Thoracic radiography—may be helpful after pleural drainage to reveal the extent of the pneumonia

Other Diagnostic Procedures!!navigator!!

  • Cytology (including Gram stain) and culture of TTA and pleural fluid. TTA is more reliable for the positive identification of pulmonary pathogens
  • Pleural fluid glucose concentration of <40 mg/dL, pH <7.2, or lactate level higher than venous blood suggest septic effusion
  • Arterial blood gas

Treatment ⬆ ⬇

TREATMENT

  • Mild cases with minimal fluid accumulation can be treated as outpatients. Hospitalization is recommended for any patient with significant fluid accumulation
  • Polyionic fluids and oxygen insufflation may be required
  • Repeated thoracic drainage or placement of an indwelling thoracic drain may be necessary

Medications ⬆ ⬇

Outline

MEDICATIONS

Drug(s) of Choice!!navigator!!

  • Optimally, antimicrobial therapy should be based on identification of the pathogens and in vitro sensitivity testing. However, therapy is usually begun prior to definitive results and broad-spectrum drugs should be used owing to the high number of mixed infections
  • Penicillin, ampicillin, and cephalosporins are effective against S. zooepidemicus. Penicillin is effective against the great majority of anaerobes but not against Bacteroides fragilis, a common anaerobic isolate. Common initial treatment choices would include penicillin or ampicillin and gentamicin or amikacin (or enrofloxacin in adult patients with compromised renal function), and metronidazole. Ceftiofur and metronidazole can be an option in milder cases
  • NSAIDs—to reduce inflammation and provide analgesia
  • Antithrombotic drugs—heparin and aspirin have been used but their use is controversial
  • Intrapleural fibrinolytics have been used in a limited number of cases. Recombinant tissue plasminogen activator is reported to improve drainage in cases with organizing fibrin

Contraindications/Possible Interactions!!navigator!!

The nephrotoxicity of aminoglycosides may be potentiated by dehydration and NSAIDs.

Follow-up ⬆ ⬇

Outline

FOLLOW-UP

Patient Monitoring!!navigator!!

Frequent auscultation and thoracic US examinations are the most sensitive indicators.

Prevention/Avoidance!!navigator!!

  • Avoid risk factors
  • Vaccination against upper respiratory viruses

Possible Complications!!navigator!!

  • Pulmonary or subpleural abscesses are not uncommon.
  • Bronchopleural fistulas, pleural adhesions, and pericarditis
  • Laminitis is a common serious sequela

Expected Course and Prognosis!!navigator!!

Guarded to good prognosis with early diagnosis and aggressive antibacterial and supportive treatment. Prognosis is guarded to poor in cases that reach the subacute to chronic stage prior to accurate diagnosis.

Miscellaneous ⬆ ⬇

MISCELLANEOUS

Abbreviations

  • NSAID = nonsteroidal anti-inflammatory drug
  • TTA = transtracheal aspirate
  • US = ultrasonography, ultrasound

Suggested Reading ⬆ ⬇

Reuss SM, Giguere S. Update on bacterial pneumonia and pleuropneumonia in the adult horse. Vet Clin North Am Equine Pract 2015;31:105–120.

Tomlinson JE, Reef VB, Boston RC, Johnson AL. The association of fibrinous pleural effusion with survival and complications in horses with pleuropneumonia (2002–2012): 74 cases. J Vet Intern Med 2015;29:1410–1417.

Author(s) ⬆

Author: Johanna L. Watson

Consulting Editors: Mathilde Leclère and Daniel Jean