Seroprevalence and Molecular Epidemiology of Leptospira spp. Infecting Dogs in the Yangtze River Region of China.

Leptospirosis, a globally re-emerging zoonosis caused by pathogenic Leptospira species, poses escalating public health challenges in rapidly urbanizing regions. Canines, as significant reservoir hosts, are increasingly regarded as effective sentinels for human leptospirosis risk. This study assessed the seroprevalence of pathogenic Leptospira in dogs across multiple provinces and regions along the Yangtze River in China. From 2021 to 2023, a total of 1517 canine serum samples were collected from Shanghai, Jiangsu, Anhui, Jiangxi, Hunan, Hubei, Chongqing, Sichuan, and Yunnan. In addition, a tissue sample was obtained from an infected dog, leading to the successful isolation and culture of one Leptospira strain. Microscopic agglutination test (MAT) results indicated an overall seroprevalence of 46.41% (704/1517), predominantly involving L. interrogans serogroups Canicola (72.73%, 512/704) and Icterohaemorrhagiae (28.68%, 202/704), followed by Ballum (18.04%, 127/704) and Australis (17.90%, 126/704). Organ examination and histopathological analysis identified severe pulmonary hemorrhage induced by the isolated strain as the primary cause of canine mortality. Whole-genome sequencing (WGS) and multilocus sequence typing (MLST) based on seven housekeeping genes classified the isolate as L. interrogans serovar Australis, sequence type (ST) ST93. These findings reveal a high seroprevalence of pathogenic Leptospira in dogs within the Yangtze River region, consistent with the distribution of locally prevalent serogroups, and underscore the potential public health risk posed by this zoonotic pathogen in the area.