Serum amyloid A concentrations in horses with acute equine piroplasmosis caused by Babesia caballi or Theileria equi

Equine piroplasmosis is a widespread tick-borne disease caused by Babesia caballi and Theileria equi. Clinical signs are non-specific and include fever, inappetence, icteric mucous membranes and lethargy; typical laboratory changes are hemolytic anemia and thrombocytopenia. Affected horses may become chronic carriers, which sometimes lead to unnecessary treatment in asymptomatic cases. Serum amyloid A (SAA) is a major equine acute-phase protein and a sensitive biomarker of inflammation. Well studied in bacterial and inflammatory conditions, its value in equine piroplasmosis remains unclear. Here, we investigated SAA concentrations in horses acutely infected with Babesia caballi or Theileria equi and compared to healthy horses. We included 25 horses: 10 healthy controls, 6 Babesia caballi-positive horses and 9 Theileria equi-positive horses. SAA concentrations were measured using a point-of-care immunoassay, and infection status (Babesia / Theileria) was determined using a loop-mediated isothermal amplification assay. We also performed ancillary diagnostic tests to exclude concurrent diseases. We found that SAA concentrations were significantly higher in horses positive for Babesia (p = 0.001) and Theileria (p = 0.001) compared to controls, with a respective increase of approximately 2312 µg/L (95% CI: 2234.0 to 2389.6 µg/L; p