Pathogenic characteristics of a novel intranuclear coccidia in Japanese black calves and its genetic identification as Eimeria subspherica.

Bovine intranuclear coccidiosis is caused by the protozoans Eimeria alabamensis and Cyclospora spp. Here, we characterized the disease and genetically identified the causative species in Japanese black calves with chronic and refractory watery diarrhea. Histologic examinations revealed atrophy of the jejunal villi and numerous parasites in the nucleus of epithelial cells in the jejunum. Based on molecular analyses using 18S ribosomal RNA gene-specific primers that we designed, the parasites were found to be formed in the same cluster as Eimeria subspherica in the phylogenetic tree, which was separated from those of other related Eimeria spp. These results constitute the first report of E. subspherica as a cause of bovine intranuclear coccidiosis.