Impact of levels of parasitemia and antibodies, acute-phase proteins, as well as stays abroad on hematological and biochemical parameters in 342 dogs with acute Babesia canis infection

Abstract

Background: Babesia canis infections are of rising importance in Germany. This retrospective study aimed to correlate hematological and biochemical parameters with acute-phase proteins, levels of parasitemia and antibodies, as well as stays abroad in dogs with acute B. canis infection. Methods: Dogs in Germany tested PCR-positive for B. canis and negative for Anaplasma phagocytophilum from January 2018 to December 2024 were included if data on hematocrit, leukocytes, and platelets were available. Hematological scoring (HES) was performed by addition of points for mild (+ 1), moderate (+ 2), and marked (+ 3) anemia, thrombocytopenia, and leukopenia, as well as for the presence of pancytopenia (+ 3) and leukocytosis (+ 1). Results of biochemical and CRP analysis, Babesia antibody determination, and pathogen quantification were included, if available. P ≤ 0.05 in Spearman’s rank correlation was considered statistically significant. Results: 342 dogs were included. History of stays abroad was known for 191/342 dogs (55.8%; no stays abroad 113/191 (59.2%), imported 55/191 (28.8%), travel 23/191 (12.0%)). The most common clinicopathologic findings were increased CRP (87.4%), thrombocytopenia (85.1%), anemia (78.7%), hyperbilirubinemia (74.2%), decreased iron levels (51.1%), and leukopenia (49.7%). Dogs without stays abroad showed significantly higher HES (n = 113, median: 6), CRP (n = 60, median: 116.2 mg/l), and levels of parasitemia (n = 92, median: 2916 × 103 parasites/ml), but lower serum antibody levels (n = 59, median: 1.5 TE) compared with imported dogs (HES: n = 55, median: 2; CRP: n = 23, median: 40.0 mg/l; levels of parasitemia: n = 29, median: 23 × 103 parasites/ml; antibodies: n = 37, median: 60.6 TE) (P < 0.001 each). Positive correlations were found between CRP and levels of parasitemia (ρ = 0.444), CRP and HES (ρ = 0.406), as well as levels of parasitemia and HES (ρ = 0.348), while negative correlations were observed between levels of antibodies and parasitemia (ρ = −0.666), as well as antibody levels and HES (ρ = −0.652) (P < 0.001 each). Conclusions: About 60% of dogs with acute B. canis infection had no history of stays abroad, thus representing autochthonous infections. Most dogs without stays abroad were immunologically naive, in contrast to most imported dogs showing positive and high antibody levels. Dogs with high antibody levels showed less severe clinicopathological alterations and lower levels of parasitemia in the peripheral blood, explained by protective antibody activity.