A significant outbreak of leptospirosis in Los Angeles County in 2021 affected over 200 dogs, revealing critical gaps in vaccination practices and raising alarms about the potential for disease transmission to humans. The study, led by researchers from the University of California, Davis, published in the Journal of Clinical Microbiology, identified crowded dog daycare facilities as key environments for the outbreak. Leptospirosis, caused by the bacterium Leptospira interrogans, can lead to severe illness in dogs and is transmissible to humans through contaminated animal urine. Despite no human cases being directly linked to this outbreak, experts warn that the disease is likely underdiagnosed in people. Investigations are now expanding to areas such as Berkeley and Oakland, where environmental conditions and interactions between wildlife and domestic animals may create new transmission pathways. The findings underscore the importance of vaccinations, with major veterinary organizations now recommending annual leptospirosis vaccinations for all dogs to protect both animal and public health.