Acute interstitial pneumonia in foals: A severe, multifactorial syndrome with lung tissue recovery in surviving foals.
Authors: Punsmann Sophia, Hoppe Judith, Klopfleisch Robert, Venner Monica
Journal: Equine veterinary journal
Summary
# Acute Interstitial Pneumonia in Foals: Understanding a Multifactorial Disease with Encouraging Prognosis for Survivors Acute interstitial pneumonia (AIP) remains poorly characterised in the equine literature, with considerable disagreement about underlying causes and limited evidence on long-term outcomes in surviving foals. This case series examined nine affected foals from a single breeding farm through clinical assessment, post-mortem examination, and detailed histopathology, including paired samples from two foals that recovered from the acute phase. Seven foals died with severe respiratory distress and fever; ultrasound typically revealed comet-tail artefacts in lung tissue. Microbiological investigation identified multiple bacterial pathogens (most commonly *Escherichia coli*, *Rhodococcus equi* and *Klebsiella pneumoniae*), whilst equine herpesvirus 2 was detected in all nine foals by PCR, with high viral loads correlating to characteristic viral-induced histopathological changes. Critically, *Pneumocystis carinii* was present in every acutely affected foal. Histologically, foals that died showed severe parenchymal collapse and necrosis, whereas recovered foals demonstrated near-complete regeneration of normal lung structure with minimal residual changes. The condition appears multifactorial rather than monocausal, suggesting that successful management and recovery may be possible with appropriate intervention, though the endemic nature of pathogens on this single farm limits generalisation to other populations.
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Practical Takeaways
- •Acute interstitial pneumonia in foals requires investigation of multiple potential triggers (viral, bacterial, environmental) rather than assuming single etiology; high mortality (78%) emphasizes need for rapid diagnosis and treatment
- •Foals that survive the acute phase can achieve complete lung regeneration with no permanent damage, providing prognostic hope for intensive care management
- •Equine herpesvirus 2 and Pneumocystis carinii appear universally involved; consider viral diagnostics and co-infections when assessing severely dyspneic foals with interstitial patterns on ultrasound
Key Findings
- •Seven of nine foals died acutely with severe respiratory distress and fever; two foals recovered completely with normal lung regeneration
- •Equine herpesvirus 2 detected in all foals by PCR, with high viral loads correlating to histopathological evidence of viral infection
- •Acute interstitial pneumonia is multifactorial, with Escherichia coli, Rhodococcus equi, and Klebsiella pneumoniae as common bacterial pathogens
- •Surviving foals showed complete lung parenchyma regeneration with nearly normal alveolar structure, indicating full recovery potential