Serum IgE, IL-4 and IL-13 Concentrations as Th2-Associated Biomarkers in Canine Giardiasis

Giardia duodenalis is a common intestinal protozoan parasite in dogs, but the systemic immune response associated with canine giardiasis remains incompletely characterized. This study aimed to evaluate serum concentrations of immunoglobulin E (IgE), interleukin-4 (IL-4), and interleukin-13 (IL-13) as Th2-associated immune markers in naturally infected dogs. Thirty client-owned dogs with confirmed giardiasis and 10 clinically healthy control dogs were included in the study. Serum IgE, IL-4, and IL-13 concentrations were measured using canine-specific enzyme-linked immunosorbent assays. Between-group comparisons were performed using two-sided Mann–Whitney U tests, with Holm adjustment for multiple comparisons, and effect estimates were calculated using the Hodges–Lehmann method. Spearman’s rank correlation was used to assess associations among biomarkers within each group. Serum IL-4 concentrations were significantly higher in dogs with giardiasis than in control dogs (median 38.12 [IQR 32.55–57.97] vs. 23.65 [18.86–27.90] pg/mL; Mann–Whitney U = 238.5, Holm-adjusted p < 0.001), with a Hodges–Lehmann estimated location shift of 16.31 pg/mL (95% CI: 9.80–27.47). Serum IgE concentrations were higher in dogs with giardiasis but did not remain statistically significant after Holm adjustment (1.32 [1.15–1.62] vs. 1.16 [1.02–1.33] µg/mL; Holm-adjusted p = 0.125), while IL-13 concentrations did not differ between groups (78.23 [53.05–103.42] vs. 79.05 [65.44–103.68] ng/L; Holm-adjusted p = 0.988). Within the giardiasis group, IgE, IL-4, and IL-13 concentrations were significantly and positively correlated with one another (ρ = 0.644–0.690, p < 0.001). In control dogs, only IL-4 and IL-13 were significantly correlated (ρ = 0.636, p = 0.048). These findings provide evidence consistent with altered Th2-associated immune activity in canine giardiasis, characterized by a significant elevation of serum IL-4 and coordinated variation among Th2-associated biomarkers. The non-significant findings for serum IgE and IL-13 may reflect a selective pattern of systemic Th2-associated biomarker expression, although limited statistical power prevents exclusion of smaller between-group differences. Further studies incorporating intestinal mucosal measurements and longitudinal assessment are warranted to clarify the relationship between systemic and local immune responses in canine giardiasis.