Asymptomatic outdoor dogs can be carriers of Babesia canis, but data describing the development of an acute phase response (APR) are not available. We hypothesised that these dogs have a moderate APR that could be detected by hematological and biochemical changes. Two groups of Babesia-exposed dogs were represented by nine B. canis PCR-positive and twenty B. canis PCR-negative, seroreactive dogs. The control group consisted of ten Babesia-naïve dogs. Serum amyloid A (SAA), paraoxonase-1 (PON-1), complete blood count, and biochemistry parameters were analysed by standard methodologies. Protein and lipoprotein fractions were separated using agarose gel electrophoresis (GE), and the dominant diameters of lipoproteins were assessed on gradient GE. Results were evaluated using non-parametric tests and the Receiver Operating Characteristic curve. SAA (median 39.0 μg/mL, range 2.2-48.8 μg/mL), total protein (median 74.7 g/L, range 57.1-98.3 g/L) and the dominant diameter of α-lipoproteins (median 13.31 nm, range 12.09-14.17 nm) in B. canis PCR-positive dogs were higher relative to dogs in the control group or dogs that were PCR-negative but seroreactive (p < 0.001 for both groups). Mild to moderate anemia (4/29), thrombocytopenia (7/29), and leukocyte counts that were close to the upper limit of the reference range were encountered in both Babesia-exposed groups. When compared to controls, Babesia-exposed dogs displayed decreased a PON-1 activity and protein GE pattern consistent with low-grade chronic inflammation (p < 0.001 for both groups). Dogs with detectable amounts of B. canis DNA in blood contain increased levels of SAA and total protein along with α-lipoproteins that display an increased diameter relative to those dogs with positive Babesia serology but undetectable levels of B. canis DNA in blood.
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