We investigated intra-annual variability in acarine parasite load (species richness, prevalence and abundance) and spleen mass in populations of leaf-nosed bats in highly seasonal tropical and subtropical climates: one population of California leaf-nosed bat (Macrotus californicus) in a subtropical thorn forest, one population of Waterhouse's leaf-nosed bat (M. waterhousii) in a subtropical desert, and one population of Waterhouse's leaf-nosed bat in a tropical deciduous forest. We tested the hypothesis that hosts in highly seasonal tropical and subtropical climates exhibit significant seasonal changes in immune response and parasite load. Prevalence was 100% in most populations examined, except in the subtropical population of M. waterhousii in the rainy season. The tropical population had the highest parasite richness in both seasons and presented species belonging to the four acarine orders examined: Mesostigmata, Ixodidae, Trombidiformes, and Sarcoptiformes. Abundance values of Trombidiformes in M. californicus, and of Ixodida and Sarcoptiformes in the tropical M. waterhousii population were higher in the rainy than in the dry season. Spleen mass was larger in the tropical population in the rainy season and in the subtropical population in the dry season. Spleen mass was not related to abundance of any of the acarine orders (Mesostigmata, Ixodidae, Trombidiformes, and Sarcoptiformes) analyzed. Our findings suggest that bats in highly seasonal tropical and subtropical environments experience significant seasonal changes in parasite burden and in immune response.