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| Leptospirosis is a bacterial disease that can cause severe illness in dogs, including acute kidney injury. These three doberman pinscher dogs were among other dogs at a homeless encampment in Oakland. Without vaccinations, they could be at risk of leptospirosis. Photo Credit: University of California, Davis |
Scientific Frontline: Extended "At a Glance" Summary: Dog Daycare Leptospirosis Outbreak
The Core Concept: A massive 2021 outbreak of leptospirosis—a severe bacterial disease that can cause acute kidney injury—sickened over 200 dogs linked to daycare facilities in Los Angeles County.
Key Distinction/Mechanism: While leptospirosis is typically contracted through environmental exposure to contaminated water or rodent urine, this specific outbreak was characterized by atypical, rapid dog-to-dog transmission within crowded, post-pandemic boarding and daycare environments.
Origin/History: Peaking in 2021 on the westside of Los Angeles, the outbreak was recently analyzed by UC Davis researchers in a May 2026 report published in the Journal of Clinical Microbiology, which traced the infections back to 59 confirmed cases across two specialty veterinary centers.
Major Frameworks/Components:
- Leptospira interrogans serovar Canicola: The specific bacterial strain identified as the cause of the outbreak, which is one of the four strains covered by standard dog leptospirosis vaccines.
- Environmental and Proximity Risks: Overcrowded daycare facilities and potential rodent infestations acted as the primary catalysts for the accelerated spread.
- Vaccination Gaps: Because Los Angeles has a historically arid climate, veterinarians previously considered leptospirosis a low risk, resulting in a highly vulnerable, unvaccinated canine population.
- The "One Health" Paradigm: The study frames the outbreak as an interconnected issue spanning animal, human, and environmental health, noting the disease affects diverse settings from affluent daycares to homeless encampments.
Branch of Science: Veterinary Medicine, Epidemiology, Infectious Diseases, and Public Health.
Future Application: The research establishes a foundation for updated veterinary protocols—specifically universal annual leptospirosis vaccinations for dogs—and aids in predicting zoonotic disease pathways as climate change and urban flooding expand bacterial habitats.
Why It Matters: Leptospirosis is a zoonotic disease that can be transmitted from animals to humans, causing severe flu-like symptoms. Identifying the root causes of this outbreak exposes critical vulnerabilities in animal vaccination practices and highlights a growing, underdiagnosed public health threat.
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| A dog at a homeless encampment in Berkeley. UC Davis researchers are investigating cases of leptospirosis in dogs in homeless encampments and providing vaccinations. Photo Credit: University of California, Davis |
A 2021 outbreak of leptospirosis that sickened more than 200 dogs in Los Angeles County reveals critical gaps in vaccination practices and raises broader concerns about the spread of the disease between animals and people, according to new research led by the University of California, Davis.
Leptospirosis is a bacterial disease that can cause severe illness in dogs, including acute kidney injury. In severe cases, the disease can be fatal. Humans can also contract the disease through contact with contaminated animal urine (especially from rodents or livestock) or contaminated water. Human cases often result in flulike symptoms that can be treated with antibiotics.
In the new study, scientists traced the outbreak to dog daycare environments, where close contact among animals could have accelerated dog-to-dog transmission—an atypical occurrence.
“We know that the boarding itself was a risk factor,” said lead author Jane Sykes, professor of small animal internal medicine at the UC Davis Weill School of Veterinary Medicine. “It might have been rodent problems in those facilities, or it might have just been really overcrowded facilities with lots of dogs in close contact with one another.”
Daycare Environments Accelerated Spread
During the peak of the outbreak, some veterinary clinics were seeing more than one case of leptospirosis per day in dogs that had recently been at dog daycare facilities on the Westside of Los Angeles County.
“The outbreak was massive,” Sykes said. “It might have been the biggest outbreak of leptospirosis in dogs that’s ever been recognized.”
Researchers analyzed 59 confirmed cases from two specialty veterinary centers and compared them with more than 15,000 control patients. The study confirmed the infections were caused by Leptospira interrogans serovar Canicola, one of four strains against which the canine leptospirosis vaccine provides protection.
While this strain is known to infect dogs, transmission typically occurs through contaminated environments rather than direct contact between dogs. However, conditions inside crowded daycare facilities after the COVID-19 pandemic could have changed that dynamic.
Lack of Vaccinations Played Key Role
The findings underscore the importance of vaccinations and vigilance in settings where dogs congregate.
“At the time, Los Angeles–area veterinarians rarely offered leptospirosis vaccinations because the bacteria thrive in water from heavy rainfall, and L.A. is an arid climate,” Sykes said. “It was considered a low risk.”
As vaccination rates increased and some dog daycares temporarily closed, the outbreak subsided. Major veterinary organizations now recommend an annual leptospirosis vaccination for all dogs.
Leptospirosis is a bacterial disease that can cause severe illness in dogs, including acute kidney injury. These three Doberman pinschers were among other dogs at a homeless encampment in Oakland. Without vaccinations, they could be at risk of leptospirosis. (UC Davis)
Disease Not Limited to Los Angeles
While the Westside of Los Angeles outbreak was centered in high-end dog daycare facilities, researchers are now investigating cases in homeless encampments in Berkeley and Oakland, where dogs, wildlife, and environmental conditions are creating new pathways for transmission.
“This disease—there’s no boundaries for it,” Sykes said. “We’re talking about dogs with this disease owned by wealthy people in L.A. and dogs that are in homeless encampments on the streets of Berkeley dying with this disease because of rodent exposure.”
Early findings from investigations in the Bay Area show high infection rates in local rat populations. Rats are the most likely reservoir hosts for Leptospira bacteria.
Public Health Implications
Dogs in encampments often roam between locations and may end up in shelters, increasing the risk of exposure to other animals and people. Although no human cases were linked to the Los Angeles outbreak, experts say the disease is likely underdiagnosed in people. In recent years, leptospirosis has been recognized in people in large U.S. cities, albeit rarely.
“It’s probably the tip of the iceberg,” Sykes said. “There are probably more unrecognized cases than we know about.”
Leptospirosis is also expected to become more common as climate change brings more flooding.
Researchers emphasize that vaccination is the most effective way to protect dogs and reduce the risk of transmission to people.
“This is a really important One Health problem,” Sykes said. “It affects dogs, and it affects people.”
Published in journal: Journal of Clinical Microbiology
Authors: Max W. Randolph, Jarlath E. Nally, Sean K. Yoshimoto, Betty Chow, David M. Wagner, Nathan E. Stone, Jason W. Sahl, Camila Hamond, Karen LeCount, Tod Stuber, Hans van der Linden, Krystle Reagan, Alexander Schrieber, Jamie Sebastian, and Jane E. Sykes
Source/Credit: University of California, Davis | Amy Quinton
Edited by: Scientific Frontline
Reference Number: vet052726_01