First report of Ribeiroia ondatrae in a Guinea Fowl (Numida meleagris): Expanding the host range of a trematode.

This report documents the first identification of Ribeiroia ondatrae in a guinea fowl (Numida meleagris), from Sacramento, California, in 2023. This finding expands the known host range of this trematode. The affected bird presented with progressive anorexia, diarrhea, and oronasal mucoid discharge, and was humanely euthanized for postmortem examination. Gross lesions included proventriculitis with mucus accumulation and obstruction of the ventriculus by koilin fronds. Microscopically, numerous flukes invaded the mucosal glands and submucosal stroma, surrounded by cellular infiltration, bacterial colonies, and necrotic debris. Morphological features were consistent with Ribeiroia ondatrae including a tongue-shaped body, alternating rows of tegumental spines, a ventral sucker anterior to the midbody, tandem elongated testes, and vitelline fields extending posteriorly. Amplification and sequencing of a 333 bp cox1 fragment showed 100% identity with Ribeiroia ondatrae sequences in GenBank. This first report of Ribeiroia ondatrae in guinea fowl highlights the need for surveillance in backyard poultry systems. Moreover, monitoring adult worms in domestic birds is recommended, as definitive hosts typically show low pathogenicity.