A leptospirosis outbreak that affected more than 200 dogs in Los Angeles County in 2021 has revealed critical gaps in vaccination practices and raised widespread concerns about the spread of the disease among animals and humans, according to a new study led by the University of California, Davis.
Leptospirosis is a bacterial disease that can cause serious illness in dogs, including acute kidney injury. In severe cases, the dog may die. Humans can also contract the disease through contact with contaminated animal urine (especially urine from rodents and livestock) or contaminated water. In humans, it often causes flu-like symptoms that can be treated with antibiotics.
In the new study, scientists traced the cause of the outbreak in a dog daycare setting, where close contact between animals may have accelerated dog-to-dog transmission, which is not a typical occurrence.
We know that boarding itself is a risk factor. Those facilities may have had a rodent problem, or they may simply have been really overcrowded facilities with lots of dogs in close contact with each other. ”
Jane Sykes, first author, professor of small animal internal medicine at the University of California Davis Weill School of Veterinary Medicine
The study was published in the Journal of Clinical Microbiology, a journal of the American Society for Microbiology.
Accelerating the spread of childcare environments
At the peak of the outbreak, some veterinary clinics were experiencing multiple cases of leptospirosis a day from dogs recently admitted to dog day care facilities in western Los Angeles County.
“The outbreak was massive,” Sykes said. “This may have been the largest outbreak of canine leptospirosis ever confirmed.”
Researchers analyzed 59 confirmed cases from two specialized veterinary medical centers and compared them to more than 15,000 control patients. Research has confirmed that the causes of infection are: Interrogation of Leptospira Serovar Canicola is one of four strains protected by canine leptospirosis vaccines.
This strain is known to infect dogs, but transmission usually occurs through contaminated environments rather than direct contact between dogs. But conditions inside crowded child care facilities after the coronavirus pandemic may have changed that dynamic.
Lack of vaccination played an important role
The findings highlight the importance of vaccination and vigilance in areas where dogs congregate.
“At that time, veterinarians in the Los Angeles area rarely offered leptospirosis vaccinations because the bacteria thrives in water from heavy rains and Los Angeles has a dry climate,” Sykes said. “The risk was considered low.”
The outbreak subsided as vaccination rates increased and some dog daycare centers were temporarily closed. Major veterinary organizations now recommend annual leptospirosis vaccination for all dogs.
The disease is not limited to Los Angeles
The West Los Angeles outbreak centered around an upscale dog day care facility, but researchers are now investigating cases at homeless camps in Berkeley and Oakland, where dogs, wildlife and environmental conditions create new transmission routes.
“This disease knows no boundaries,” Sykes said. “We’re talking about dogs with this disease owned by wealthy people in Los Angeles and dogs in homeless encampments on the streets of Berkeley dying from this disease because of exposure to rodents.”
Early results from research in the Bay Area indicate high infection rates among local rat populations. Rats are the most likely host for leptospirosis.
Public health impact
Dogs in camps often roam between locations and may end up in shelters, increasing the risk of contact with other animals and people. While the Los Angeles outbreak has not resulted in confirmed human infections, experts say the disease is likely underdiagnosed in people and that leptospirosis has been identified in rare cases in people in large U.S. cities in recent years.
“This is probably the tip of the iceberg,” Sykes said. “There are probably many more unrecognized cases than we know about.”
As climate change increases flooding, leptospirosis is also expected to become more common.
Researchers emphasize that vaccination is the most effective way to protect dogs and reduce the risk of infection to humans.
“This is a very important issue for One Health,” Sykes said. “It affects dogs, it affects humans.”
Other authors from the University of California, Davis include Max W. Randolph and Krystle Regan. No funding was received for this study.
sauce:
University of California, Davis
Reference magazines:
Randolph, M.W.; others. (2026). 2021 Clinical and Molecular Characterization of Leptospirosis in Dogs in Los Angeles County, California, USA. Journal of Clinical Microbiology. DOI: 10.1128/jcm.00240-26. https://journals.asm.org/doi/10.1128/jcm.00240-26
