In April 2020, an outbreak of diarrhea occurred in lactating cows at a dairy farm in the Tottori Prefecture. Five cows died, and Listeria monocytogenes was isolated from the liver, spleen, kidney, and jejunum of one affected cow that was subjected to bacteriological examination. Pathological examination revealed liver necrosis. Histopathologically, the primary lesions were characterized by multifocal necrotizing hepatitis. Small bacilli were immunohistochemically identified within the necrotic hepatic lesions, as well as the jejunal villi and central lacteals. The diagnosis was confirmed as septicemic bovine listeriosis. Subsequently, five L. monocytogenes-suspected abortions and multiple cases of mastitis occurred on the farm. The L. monocytogenes strains isolated from the affected cow and the abortion and mastitis cases were all serotype 4b; their sequence type, determined by multi-locus sequence typing, was ST1, and their clonal complexes were CC1. This case was considered an extremely rare outbreak in which the same strain of L. monocytogenes caused diverse symptoms, such as septicemia and diarrhea.
