A case of concurrent infection with bovine viral diarrhea virus and Salmonella enterica Serovar Typhimurium and its monophasic variant in a beef calf rearing farm.

Abstract

In July 2022, an outbreak characterized by fever, diarrhea, and mortality occurred among suckling calves at a beef calf-rearing farm in Tottori Prefecture in Japan. A monophasic variant of Salmonella enterica serovar Typhimurium (Salmonella 4,[5],12:i:-) was subsequently isolated from a deceased calf. In August 2022, a persistently infected (PI) calf with bovine viral diarrhea virus (BVDV) was identified and subsequently euthanized. Between June and September 2022, the median number of treatments administered per month per calf in the calf-hutch area tended to be higher (P<0.20) and the mortality rate was significantly higher (P<0.05) compared with the same period in 2021. In this outbreak, the PI calf introduced to the farm likely transmitted BVDV to other suckling calves; the resulting immunosuppression may have exacerbated the clinical manifestations of concomitant Salmonella 4,[5],12:i:- infection, leading to substantial production losses on the farm. To our knowledge, this is the first report of a herd-level concurrent infection with BVDV and Salmonella 4,[5],12:i:- in Japan.