Administration of commercial Rhodococcus equi specific hyperimmune plasma results in variable amounts of IgG against pathogenic bacteria in foals.
Authors: Sanz M G, Oliveira A F, Page A, Horohov D W
Journal: The Veterinary record
Summary
Rhodococcus equi remains the leading infectious cause of pneumonia in foals, yet the lack of an effective vaccine means that commercial hyperimmune plasma (HIP) products are frequently administered as a preventive strategy despite inconsistent evidence supporting their use. Sanz and colleagues analysed three different lots from four commercial R equi HIP products and measured virulence-associated protein A (VapA)-specific antibody responses in both the plasma preparations and in 97 foals receiving HIP, compared with 70 control foals; they employed ELISA methodology to quantify IgG and IgG subclass concentrations. Whilst HIP administration did significantly increase VapA-specific IgG levels in recipient foals (P<0.001), the variation between foals receiving identical products was marked, with coefficients of variation ranging from 17 to 123 per cent between different lots and statistically significant differences observed between products themselves (P<0.001). These findings provide a plausible explanation for the widely reported and frustrating variability in clinical outcomes following HIP use, suggesting that lot-to-lot inconsistency in antibody titres may substantially undermine protective efficacy. Practitioners should be aware that whilst HIP administration will boost foal immunity against R equi, the quality and potency of different products—and even different batches of the same product—cannot be assumed equivalent, making standardised dosing protocols less reliable than currently practised.
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Practical Takeaways
- •Hyperimmune plasma administration does increase foal immunity against R. equi, but expect variable results even with the same product due to batch variation
- •When using commercial R. equi HIP, consider testing specific batches for antibody content if resources permit, as coefficients of variation suggest substantial differences between lots
- •The inconsistent efficacy reported for HIP in preventing R. equi pneumonia in foals may be partly explained by variability in antibody concentration within and between commercial products
Key Findings
- •Commercial R. equi hyperimmune plasma significantly increased VapA-specific IgG in recipient foals (P<0.001), but with marked variation between individual foals receiving the same product
- •VapA-specific IgG concentrations varied significantly between different HIP products (P<0.001) with coefficients of variation ranging from 17-123%
- •Substantial lot-to-lot variation in VapA-specific IgG content within the same commercial HIP product was observed
- •Variable antibody transfer from HIP may explain previously documented inconsistencies in clinical efficacy of hyperimmune plasma for R. equi prevention