Air sampling in the breathing zone of neonatal foals for prediction of subclinical Rhodococcus equi infection.
Authors: Chicken C, Muscatello G, Freestone J, Anderson G A, Browning G F, Gilkerson J R
Journal: Equine veterinary journal
Summary
# Editorial Summary Rhodococcus equi pneumonia remains a significant economic and welfare concern in foal populations, yet early detection is hampered by the disease's subtle onset and lack of reliable diagnostic markers. Chicken and colleagues investigated whether sampling bacteria from the breathing zone of neonatal foals (≤10 days old) could predict which individuals would subsequently develop clinical pneumonia, collecting air samples at two timepoints and correlating findings with ultrasonographic screening at 1–2 months of age. Virulent R. equi was identified in breathing zone air from 19% of neonates and 45% of older foals, but crucially, detection bore no relationship to which foals developed pneumonia (diagnosed in 23% of the cohort), with median bacterial concentrations indistinguishable from background environmental samples across all groups. For practitioners, this finding suggests that early airway sampling of neonates offers no predictive advantage over routine ultrasound screening and should not substitute for established surveillance protocols in young foals. However, the elevated detection rates in older foals indicate that breathing zone culture may retain value as a herd-level epidemiological tool for understanding environmental contamination and infection dynamics on breeding establishments.
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Practical Takeaways
- •Do not rely on air sampling from young foal breathing zones as a predictor of which foals will develop rhodococcal pneumonia—ultrasonographic screening remains the preferred early detection method
- •Air sampling may still have value as a herd-level epidemiological tool for older foals, but should not guide individual foal diagnosis or treatment decisions in neonates
- •Continue using routine ultrasonographic screening at 1-2 months of age as the standard for early detection of subclinical rhodococcal pneumonia in breeding operations
Key Findings
- •Virulent R. equi was detected in breathing zone air of 19% of neonatal foals and 45% of foals aged 1-2 months, but there was no association with subsequent ultrasonographic diagnosis of pneumonia
- •Median concentration of virulent R. equi in breathing zone air of neonates (0 cfu/250 l) and older foals (0 cfu/250 l) was not significantly different from background air samples (0 cfu/250 l)
- •23% of foals were diagnosed with rhodococcal pneumonia ultrasonographically, but air sampling did not predict which foals would develop clinical disease
- •Air sampling from breathing zone of foals ≤2 months old is not a superior diagnostic tool compared to early ultrasonographic screening for detecting rhodococcal pneumonia