Trichomitus batrachorum is a species of trichomonad that has gained attention due to its ecological importance and potential interactions with various hosts, such as amphibians (anurans) and reptiles (lizards and chelonians), where it has been recorded in the gastrointestinal tract of these vertebrates, specifically in their feces. Molecular studies have placed this flagellated protist within the Metamonada clade. Unlike parabasalids that inhabit endothermic mammals in relatively stable temperature conditions, protists associated with ectothermic reptiles are subject to significant temperature fluctuations. The ability of T. batrachorum to thrive in the variable temperatures encountered by reptiles suggests that its parasitism may remain largely unaffected by climate change. In our study, we detected and characterized T. batrachorum from the liver tissue of the lizard species Ameiva ameiva, collected in Presidente Figueiredo Municipality, Amazonas State, Brazil. The identification of T. batrachorum was confirmed by cultivation technique, light microscopy, scanning electron microscopy and transmission electron microscopy for ultrastructural analyses, and sequencing the 5.8S rDNA (region ITS1- ITS2) and 18S rRNA (ribosomal RNA) genes. One potential interpretation for this finding is that the flagellates may have migrated from the intestine to the bile duct, ultimately reaching the liver. This is the first successful characterization of T. batrachorum in the liver of a lizard, and provides a solid foundation for further research to elucidate the potential pathogenicity of this flagellate and the role of A. ameiva in the epidemiology of parabasalids in other animal species.

The microbial communities associated with muscid flies have gained increased attention due to their changing composition across developmental stages, which is significantly influenced by environmental factors and available food sources. In this context, Musca domestica L. stands out as one of the most relevant species, primarily recognized as a mechanical vector of infectious agents, including bacteria, protozoa, and viruses. Some of these agents can be transmitted to humans and animals, causing disease, largely due to the species frequent association with decomposing organic matter and contaminated environments, thereby facilitating the dissemination of microorganisms. Among the microorganisms that share these same environments, the eukaryotic protozoan genus Acanthamoeba deserves special attention. However, despite this environmental coexistence, current knowledge regarding Acanthamoeba species and their interactions with insects remains limited and fragmented, highlighting the need for further studies to clarify the specific role of flies in the epidemiology of Acanthamoeba infections. In this context, the occurrence of Acanthamoeba species. was investigated in wild populations of M. domestica. Flies were collected using traps distributed throughout the FIOCRUZ/RJ campus. 14 (28%) of the 50 flies examined tested positive for Acanthamoeba and were identified as genotype T4 by Sanger sequencing of the 18S rRNA gene, a genotype commonly associated with keratitis. Active Acanthamoeba trophozoites were detected in the intestines of five flies. These findings reinforce the importance of understanding the ecological relationship between Acanthamoeba and M. domestica, given the potential role of these flies as environmental vectors in the dissemination of pathogens that may impact human health.