A probable cluster of premature birth and stillbirth caused by Leptospira interrogans serogroup Hebdomadis in an integrated swine farm in Nagasaki Prefecture, Japan.

In an integrated swine farm with 135 sows in Nagasaki Prefecture, premature births and stillbirths were observed in six sows in June and July 2023, and their etiology was investigated. Leptospiral flaB gene was detected in the kidney of one stillborn fetus and the placenta of its sow by nested PCR. Multilocus sequence typing revealed that the infecting strain was Leptospira interrogans ST118. In addition, leptospiral antigens were detected in lesions of the above tissues by immunohistochemical staining. The examined sow and several other sows in the farm had antibodies against serogroup Hebdomadis. These results suggested that L. interrogans serogroup Hebdomadis ST118 was the causative agent of premature births and stillbirths that occurred in this farm.