Descriptive Epidemiological Analysis for the First Outbreak of Lumpy Skin Disease in Japan in 2024

Lumpy skin disease (LSD) is a transboundary emerging disease of cattle and water buffaloes that threatens the livestock industry globally. Japan experienced its first outbreak in November 2024. This study aimed to describe the spatial and temporal characteristics of this outbreak and estimate the transmissibility using a mathematical model for within-farm transmission. The first and second cases were confirmed on dairy farms in Itoshima City, Fukuoka Prefecture, southern Japan, on November 6, 2024. Twenty-two farms were confirmed during this outbreak, with 17 cases in Itoshima City and the other two municipalities in Fukuoka Prefecture. The third case occurred in Kumamoto Prefecture on November 8, 2024, and was linked to the long-distance movement of potentially infected cattle via the livestock market from the first case on October 18, 2024. Two additional cases were detected near the third case. Control measures included isolation and voluntary culling of infected cattle; voluntary movement restrictions on infected, suspected, and apparently healthy cattle on the same premises; and voluntary suspension of the raw milk and semen shipments from infected and suspected animals. These measures were voluntary; however, no violations were reported. Vector control was achieved with insecticides and insect-proof netting. Voluntary vaccination was conducted within a 20 km radius of affected farms in Fukuoka Prefecture. Mathematical modeling of within-farm transmission dynamics revealed a transmission rate of 0.0031 (95% CI: 0.002-0.0044) per day. The basic reproduction number was 3.51 (95% CI: 2.26-4.98) based on a herd size of 49 and an infectious period of 23.1 days. Although the outbreak was geographically limited, this study highlights key epidemiological features of LSD, including its high transmission rate and long-distance transmission via cattle movement. Japan has a persisting LSD virus (LSDV)incursion risk due to recent outbreaks in Asia. Strengthening preparedness, including awareness among farmers and veterinarians, emergency vaccination plans, vector control, traceability, and quarantine protocols for cattle movement, is essential to mitigate future outbreaks.