Bacterial pneumonia
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Lower respiratory disease is a common problem in foals under 8 months of age. The most common causes of lower respiratory
disease in weanlings include 1) opportunistic bacterial pneumonia (Streptococcus zooepidemicus is the most common), 2) Rhodococcus equi pneumonia, 3) bronchointerstitial pneumonia and 4) parasitic pneumonia.
Bacterial pneumonia
R. equi
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Bacterial pneumonia: Opportunistic organisms include Strep zooepidemicus, Strep pneumoniae, Actinobacillus spp, Pasturella spp, Bordetella bronchoseptica,
Klebsiella ssp, and E. coli. Foals develop bacterial pneumonia secondary to parasitic pulmonary migration, viral respiratory disease, and stress (overcrowding,
transport and weaning).
Interstitial pneumonia
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Clinical signs: will vary on severity. Fever, depression, anorexia, and bilateral purulent nasal discharge. Advanced cases
can appear very similar to cases of R. equi or interstitial pneumonia (dyspnea, respiratory distress and cyanosis).
US – bacterial pneumonia
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Diagnostics: Thoracic radiographs can be very helpful. Thoracic radiographs may help determine the likelihood of routine bacterial
pneumonia from R. equi and interstitial pneumonia. Thoracic radiographs of bacterial pneumonia usually reveal consolidation of the cranioventral
lungs. R. equi often demonstrates perihilar abscessation and alveolization. Interstitial pneumonia appears as diffuse interstitial pneumonia
of the caudodoral lungs.
US- R equi
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Ultrasound of the thorax can also be useful to identify pleural effusion and peripheral consolidation. Ventral lung consolidation
can occur with bacterial pneumonia. Rhodococcus is be characterized with peripheral abscessation. Ultrasound will not detect
lung pathology that is deep to overlying aerated lung. Ultrasound examination of interstitial pneumonia can range from a normal
pleural border and to excessive comet tails. Severe consolidation is not usually consistent with interstitial pneumonia
Transtracheal wash is indicated to appropriately work up the pneumonia (including cytology).
US- interstitial pneumonia
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Treatment: Initially a broad spectrum antibiotic (including antibiotics specific for Strep spp). Bordetella bronchoseptica may be more difficult to treat. B. bronchoseptica is a B-lactamase producer, which results in bacterial overgrowth due to death of penicillin-sensitive organisms. Foals may
show an initial improvement with antibiotic therapy, followed by deterioration of clinical signs. Aminoglycosides are the
treatment of choice (gentamicin and amikacin). The organism lives anchored to the epithelial surface of the airway. In some
cases neubulization with gentamicin may be necessary to provide direct deliver of the antibiotic to the airway.
