Eosinophilia and leukocyte responses associated with Hepatozoon infection in the Neotropical frog Leptodactylus vastus Lutz, 1930 (Anura: Leptodactylidae).

Amphibians are among the most threatened vertebrates globally, but the physiological mechanisms underlying their vulnerability remain poorly understood, particularly in Neotropical species. This study investigated the associations among body morphometry, Hepatozoon spp. infection, and leukocyte profile of Leptodactylus vastus from the Brazilian Atlantic Forest. Sixty individuals were analyzed for hematologic and parasitic parameters. Hepatozoon spp. prevalence was 100%, and the leukocyte profile was atypical, characterized by a predominance of eosinophils over lymphocytes. Total gamont abundance correlated positively with total leukocyte count. Individuals with high total gamont abundance exhibited leukocytosis, neutrophilia, and lymphopenia, as well as an increased neutrophil-to-lymphocyte ratio. Snout-vent length was a positive independent predictor of total gamont abundance, total leukocyte count, and neutrophils. This study provides the first hematologic and leukocyte characterization of Leptodactylus vastus, revealing an unusual eosinophilic profile and an inflammatory response associated with increasing total gamont abundance, with emphasis on neutrophil-to-lymphocyte ratio and lymphopenia as potential biomarkers of infection-associated physiological stress. These findings contribute to the ecoimmunological knowledge of Neotropical anurans and provide a foundation for future investigations into the effects of parasitism and anthropogenic stressors on amphibian health.