Pneumonia and Pleurisy in Adult Horses

Pleura: structure and function

• visceral and parietal layers
• single layer of mesothelial squamous cells
• overlie loose connective, and adipose tissue • Incomplete mediastinum
• 80% of horses
• fenestrated in caudal ventral portion

Identification of pleural effusion
Clinical Signs

• small amount of fluid
  • respiratory signs may be absent
• several liters of fluid
  • may be dyspneic at rest, or following slight exertion
• ventral dullness on ausculation and percussion 

Laboratory analysis

• differentiate transudate/exudate
• identify neoplastic cells 

Differential diagnosis of pleural effusion

• Pleuropneumonia
• Haemothorax
• Neoplasia particularly cranial mediastinal lymphosarcoma 
• Right-sided heart failure
• Pericarditis

PLEUROPNEUMONIA
Definition: inflammation of the mesothelial lining of pleural cavity with associated parenchymal disease due to bacterial infection

Pathogenesis

• Mixed bacterial infection
  • Organisms are often that are normal flora of the pharynx: Beta-haemolytic
    Streptococcus, E coli, Klebsiella spp. Pasteurella spp., Bordatella spp., Bacteroides spp, anaerobes
• Suppression of pulmonary defense mechanisms

• Often follows recent stressful event 

  • Prolonged shipping
  • High performance
  • Commingling with other horses 
  • Occult or patent respiratory infection 
  • Thoracic trauma
  • Surgery and general anaesthesia. [...]