Gross and histologic description of trematodosis in fetal and neonatal beef calves in North Dakota and Minnesota.

Hepatic trematodes, such as Fasciola hepatica and Fascioloides magna, have variable distribution throughout the United States. F. magna is endemic in the upper midwestern United States, and F. magna infections are diagnosed frequently in weaned calves and adult beef cattle at the North Dakota State University Veterinary Diagnostic Laboratory (NDSU-VDL). Rarely, liver fluke infestation has also been observed in much younger calves, including aborted fetuses. We describe here, in 2 fetal and 7 neonatal beef calves submitted to the NDSU-VDL between 2011 and 2020, parasitic migration tracts in livers, consisting of regionally extensive, random, linear tracts of fibrosis admixed with black porphyrin pigment, along with foci of necrosis and hemorrhage, and mixed inflammatory cells, which were caused presumptively by F. magna infection. Samples were not available from our 9 cases for PCR assay and sequencing, but we did confirm F. magna within liver samples collected from regional cattle in 2020 and 2021. Fetal and neonatal trematodosis was often concurrent with other common causes of fetal abortion and neonatal calf loss in our cases; however, based on the prepatent period of F. magna, fetal and neonatal beef calf trematode infestations occurred in utero.