Association of pneumonia with concentrations of virulent Rhodococcus equi in fecal swabs of foals before and after intrabronchial infection with virulent R. equi.
Authors: Cohen Noah D, Kahn Susanne K, Bordin Angela I, Gonzales Giana M, da Silveira Bibiana Petri, Bray Jocelyne M, Legere Rebecca M, Ramirez-Cortez Sophia C
Journal: Journal of veterinary internal medicine
Summary
# Editorial Summary The capacity of foals to resist *Rhodococcus equi* pneumonia may depend partly on their prior environmental exposure to virulent strains of the organism through natural ingestion. Researchers analysed faecal samples from 21 university-owned foals, comparing bacterial concentrations before and after experimental intrabronchial infection; five foals had been orally inoculated with live virulent *R. equi* at 2 and 4 days of age, whilst 16 served as untreated controls. Quantitative PCR targeting the virulence-associated protein A gene (*vapA*) revealed that control foals developing pneumonia harboured significantly lower faecal *R. equi* concentrations (25 copies/100 ng DNA) before infection than healthy controls (280 copies/100 ng DNA) or the pre-inoculated group (707 copies/100 ng DNA). These findings suggest that cumulative mucosal priming through natural ingestion of virulent *R. equi* in the environment may provide protective immunity against subsequent respiratory disease, implying that foals with greater faecal bacterial burden possess better immunological defences. For practitioners managing foals on endemic properties, this work indicates that preventing all environmental exposure to *R. equi* may be neither feasible nor necessarily beneficial, and selective natural exposure strategies warrants further investigation as a potential disease mitigation approach.
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Practical Takeaways
- •Natural exposure to virulent R. equi early in life may provide protective immunity against pneumonia in foals, suggesting that complete prevention of R. equi ingestion may not be beneficial
- •Fecal vapA concentrations could potentially serve as a biomarker to identify foals at higher risk for developing R. equi pneumonia
- •Management strategies should consider the potential protective effects of early, controlled exposure to environmental R. equi rather than attempting complete pathogen elimination
Key Findings
- •Foals that developed pneumonia had significantly lower fecal concentrations of virulent R. equi (vapA: 25 copies/100 ng DNA) before intrabronchial infection compared to healthy controls (280 copies/100 ng DNA) and gavaged foals (707 copies/100 ng DNA)
- •Greater natural ingestion and fecal shedding of virulent R. equi was associated with protection against subsequent experimental pneumonia in foals
- •Intragastric administration of live virulent R. equi at days 2 and 4 of life resulted in higher fecal concentrations of virulent R. equi at 28 days of age