Peripheral blood eosinophilia in dogs and cats: A cross-sectional study on prevalence, seasonality, and endoparasite infections in a referral hospital population

Peripheral blood eosinophilia is commonly interpreted in small animal practice as a potential indicator of parasitic infection, although evidence supporting this association remains limited. This study aimed to prospectively evaluate the relationship between peripheral eosinophilia and intestinal/respiratory endoparasites in dogs and cats, and to assess whether eosinophilia shows seasonal fluctuations in a referral hospital population. A cross-sectional observational study was conducted at a veterinary teaching hospital (November 2022–November 2024). Complete blood counts were screened to identify eosinophilia (≥750 cells/μL in dogs; ≥950 cells/μL in cats) and cases were assigned to meteorological seasons. Prospectively identified eosinophilic animals underwent coprological testing (pooled fecal samples) using flotation (Mini-FLOTAC®) and Baermann techniques. Eosinophilia was detected in 310/2750 (11.3%) dogs and 101/1091 (9.3%) cats. Eosinophil counts did not differ significantly across seasons in either species, and the proportion of eosinophilic animals remained stable throughout the year, with no evidence of a linear seasonal trend. In the prospective cohort, endoparasites were identified in 6/68 (8.8%) eosinophilic dogs and 3/18 (16.7%) eosinophilic cats. Eosinophil concentrations overlapped substantially between parasite-positive and parasite-negative animals. In this urban referral population, peripheral eosinophilia was common, showed no meaningful seasonal pattern, and was infrequently associated with detectable endoparasitic infection. These findings support a diagnostic-driven approach to antiparasitic treatment rather than empirical therapy based solely on eosinophil counts.