Investigation of The Usefulness of Serum Amyloid A in Characterizing Selected Disease Forms of Equine Herpesvirus-1 Infection.
Authors: Pusterla Nicola, Miller Julia, Varnell Sarah, Armstrong Warren, Frost Laura, Michon Carole, Lambert Kimberly, Whitfield Susanna, Cowles Bobby
Journal: Journal of equine veterinary science
Summary
# Editorial Summary: Serum Amyloid A as a Biomarker for Equine Herpesvirus-1 Researchers evaluated whether serum amyloid A (SAA), an acute phase protein, could differentiate between healthy horses and those infected with EHV-1 across four disease presentations: subclinical infection, respiratory disease, neurological disease, and non-infected controls. Using archived serum samples from 153 horses (48 healthy, 48 subclinically infected, 40 respiratory cases, 17 neurological cases), they measured SAA concentrations and compared values across groups. Respiratory EHV-1 cases showed the most pronounced elevation with a median SAA of 597 µg/mL (range 0–3,000), whilst neurological cases had markedly lower values at 58 µg/mL (range 0–1,640), and subclinically infected horses fell between these at 8.5 µg/mL (range 0–2,416); healthy horses remained near baseline at 0 µg/mL median. Although infected horses overall demonstrated significantly elevated SAA compared to non-infected animals, a single blood test proved unreliable for confirming subclinical infection, and the wide variability suggests SAA alone cannot definitively establish EHV-1 status. For practitioners, this indicates that whilst SAA may support diagnosis in symptomatic cases—particularly respiratory disease—it should not be used as a standalone diagnostic tool, especially in subclinically infected horses where multiple sampling points or complementary diagnostic methods remain necessary.
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Practical Takeaways
- •SAA can support diagnosis of active EHV-1 infection when elevated, but normal SAA does not rule out subclinical infection in individual horses
- •Respiratory EHV-1 disease produces markedly higher SAA responses than neurological forms, which may assist in clinical differentiation between disease types
- •Single SAA measurements have limited diagnostic value for subclinical EHV-1; serial sampling or combination with other diagnostic methods is recommended
Key Findings
- •Serum Amyloid A (SAA) values were significantly higher in infected horses (median 8.5–597 μg/mL) compared to healthy controls (median 0 μg/mL)
- •Respiratory EHV-1 infection showed the highest median SAA elevation at 597 μg/mL, compared to neurological disease at 58 μg/mL
- •Single point-in-time SAA testing was unable to reliably differentiate subclinically infected horses from healthy horses despite elevation in most infected animals
- •SAA values ranged widely within each disease group (0–3,000 μg/mL), indicating variable acute phase response across individual horses