In March 2025, gangrenous dermatitis caused by Clostridium septicum occurred on a broiler farm in Tottori Prefecture. At 37 days of age, an increased number of dead chickens exhibiting dermatitis with a foul odor was mainly observed. In chickens at 41 days of age subjected to necropsy, subcutaneous edema with gas, hepatomegaly and friability of the liver, and multifocal hepatic necrosis were observed. The final mortality rate exceeded 60%, causing significant economic losses. Clostridium septicum was isolated from the subcutaneous lesions and the liver. Severe subcutaneous hematoid edema with numerous bacilli, hepatocellular necrosis, and lymphoid depletion and follicular atrophy in the bursa of Fabricius were observed by histopathological analysis. Infectious bursal disease virus (IBDV) genes were detected by RT-PCR and restriction fragment length polymorphism revealed that the restriction patterns of the amplicons were similar to that of a variant strain (vIBDV) detected in Tottori prefecture in 2023. In this case, it was suggested that immunosuppression caused by vIBDV exacerbated the clinical symptoms of gangrenous dermatitis, leading to a high mortality rate.
