- UC Davis researchers analyzed a 2021 leptospirosis outbreak involving more than 200 dogs in Los Angeles County.
- The study found dog daycare attendance was a significant risk factor for infection.
- Investigators identified low vaccination rates as a key contributor to the outbreak.
- Researchers are also examining leptospirosis cases linked to rodent exposure in Bay Area homeless encampments.
- Experts say annual vaccination remains the most effective way to protect dogs and reduce zoonotic risk.
A new study from the University of California, Davis is drawing attention to the continued threat of leptospirosis in dogs after researchers identified vaccination gaps and dog daycare attendance as key factors in a major Los Angeles County outbreak.
Published in the Journal of Clinical Microbiology, the research examined a 2021 outbreak that affected more than 200 dogs and is believed to be among the largest recognized canine leptospirosis outbreaks reported in the United States.
Vaccination Gaps Linked to Outbreak
Researchers analyzed 59 confirmed cases from the outbreak and compared them with more than 15,000 control patients. The investigation found that many infected dogs had recently attended daycare facilities, suggesting that congregate environments played a significant role in disease transmission.
The outbreak was caused by Leptospira interrogans serovar Canicola, one of the strains included in standard canine leptospirosis vaccines.
According to the study, leptospirosis vaccination was not commonly recommended by many Los Angeles-area veterinarians at the time because the disease was considered relatively uncommon in the region’s dry climate. Researchers noted that the outbreak subsided as vaccination rates increased and some daycare facilities temporarily closed.
Ongoing Concerns Across California
While the study focused on the Los Angeles outbreak, researchers say leptospirosis remains an active concern in other parts of California.
UC Davis investigators are currently examining cases among dogs living in homeless encampments in Berkeley and Oakland, where rodent exposure may be contributing to transmission. Early findings have identified high infection rates among local rat populations, which are recognized reservoirs for the disease.
The researchers noted that leptospirosis can affect dogs in a variety of environments and is not limited to a single geographic area or population.
One Health Implications
Leptospirosis is a bacterial disease that can cause severe illness in dogs, including acute kidney injury and, in some cases, death. The disease can also infect people through exposure to contaminated animal urine or contaminated water.
Although human cases linked to the Los Angeles outbreak were not identified, researchers said the disease may be underdiagnosed in people and has increasingly been recognized in urban environments.
The study’s authors emphasized that leptospirosis represents an important One Health issue because of its impact on both animal and human health. They also noted that environmental changes, including increased flooding and rodent exposure, could contribute to future disease risks.
Researchers said routine vaccination remains the most effective strategy for protecting dogs and reducing the potential for transmission.
Information sourced from a University of California, Davis research announcement and a study published in the Journal of Clinical Microbiology.
