Molecular epidemiology of pathogenic Leptospira spp. in Thailand during 2024-2025, with detection of Leptospira weilii in human clinical specimens.

BACKGROUND: Leptospirosis is a significant zoonotic disease in Thailand and globally. The causative agents are the spirochete bacteria in the genus Leptospira. An updated assessment of molecular epidemiology in Thailand is needed. METHODOLOGY/PRINCIPAL FINDINGS: Remnant EDTA blood specimens from suspected leptospirosis cases collected between June 2024 and July 2025 from the Central, Northern, Northeastern, and Southern regions of Thailand, were referred to the National Institute of Health. Demographic data were collected. Confirmed cases were diagnosed using TaqMan real-time PCR targeting LipL32 with a positively threshold of Ct < 37. Partial 16S rDNA (approximately 500 bp) was sequenced using Oxford Nanopore (Oxford, UK) and analyze by BLASTn. Among 1,063 suspected cases, 34 (3.2%) were real-time PCR confirmed. The majority of the cases were male (58.8%), primarily residing in Nan province (55.9%), and most positives were from specimens collected during the rainy season (76.5%). Twenty-six of 34 sequences (76.5%) clustered with L. interrogans, and 8 of 34 (23.5%) clustered with L. weilii within the primary pathogenic (P1) clade. Re-examination with published Thai and regional datasets showed broad circulation of L. interrogans and a Northern Thailand-Lao People Democratic Republic (PDR) focus for L. weilii To our knowledge, this is the first evidence of L. weilii detected in human clinical specimens in Thailand. CONCLUSION/SIGNIFICANCE: Pathogenic L. interrogans and L. weilii caused human Leptospirosis in Thailand during 2024-2025. These findings update the epidemiological status of Leptospira spp. in Thailand and can guide surveillance and control.