Molecular and Histopathological Findings of Giardia duodenalis in Rodents and Bats from the Atlantic Forest and Cerrado of Southeastern Brazil

Giardia duodenalis is a globally distributed intestinal protozoan infecting humans and animals. This study investigated its occurrence, genetic diversity, and histopathological findings in rodents and bats from the Atlantic Forest and Cerrado of southeastern Brazil. A total of 518 intestinal-content samples, each obtained from a different individual animal, were screened using Sheather’s sugar flotation. Histopathological examination was performed on three tissue sections obtained from the proximal portion of the small intestine. Samples with structures morphologically compatible with Giardia cysts were subsequently subjected to nested PCR and partial β-giardin (bg) gene sequencing. Giardia cysts were detected in 13/518 animals (2.5%), including Oligoryzomys sp., O. nigripes, Thaptomys nigrita, Rattus rattus, and Carollia perspicillata. All 13 microscopy-positive samples were confirmed as G. duodenalis by DNA sequencing. Single-locus bg analysis identified 12 isolates as assemblage A, whereas one R. rattus isolate clustered with assemblage E. Because molecular testing was restricted to microscopy-positive samples, the 2.5% estimate represents microscopy-detected occurrence rather than molecular prevalence. Histopathological examination revealed predominantly mild-to-moderate intestinal changes. Structures morphologically compatible with Giardia trophozoites were observed in the submucosa of two rodents, although their identity requires specific confirmation. Detection of G. duodenalis in T. nigrita expands the documented host range, while its detection in C. perspicillata extends the documented occurrence of this parasite in this bat host to the Brazilian Atlantic Forest. These findings expand knowledge of G. duodenalis genetic circulation in free-ranging small mammals and support integrated surveillance within a One Health framework.