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• Posted May 29, 2026

Study: LA Canine Outbreak Caused By Low Vaccination Rates, Crowded Boarding

Critical gaps in vaccination and infection control led to a leptospirosis outbreak that sickened more than 200 Los Angeles County dogs in 2021, according to a new study.

The outbreak occurred at doggie daycares, where close contact between pooches likely accelerated dog-to-dog transmission, researchers reported May 26 in the Journal of Clinical Microbiology.

A lack of vaccination against leptospirosis contributed to the outbreak, researchers found.

“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,” said senior researcher Jane Sykes, a professor of small animal internal medicine at the University of California-Davis. “It was considered a low risk.”

During the peak of the outbreak, some vet clinics were seeing more than one case of leptospirosis a day coming from dogs that had recently been at doggie daycares on the west side of Los Angeles County, researchers said.

“The outbreak was massive,” Sykes said in a news release. “It might have been the biggest outbreak of leptospirosis in dogs that’s ever been recognized.”

Leptospirosis is a bacterial disease that can cause severe illness, kidney damage and even death, according to the U.S. Centers for Disease Control and Prevention (CDC).

Humans also can contract the disease through contact with contaminated animal urine or contaminated water, but no human cases were linked to the Los Angeles outbreak, researchers said.

However, experts say the disease is likely underdiagnosed in people, where it causes flu-like symptoms that can be treated with antibiotics. Rare cases have been recognized in people in large U.S. cities.

“It’s probably the tip of the iceberg,” Sykes said. “There are probably more unrecognized cases than we know about.”

At the height of the outbreak, some L.A.-area doggie daycares temporarily closed and vaccination rates increased. This caused the outbreak to eventually subside.

For the study, researchers compared 59 confirmed cases from two specialty veterinary centers with more than 15,000 healthy dogs.

Analysis confirmed the infections were caused by Leptospira interrogans serovar Canicola, which is one of the four strains that the canine leptospirosis vaccine protects against.

And while the LA outbreak was centered in high-end doggie daycares, cases also have occurred in homeless encampments in the Northern California communities of Berkeley and Oakland.

“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 the Bay Area show high infection rates in local rat populations, making them the most likely hosts for leptospirosis.

Vaccination is the most effective way to protect dogs and reduce the risk of transmission to people, researchers said.

Major veterinary organizations now recommend annual leptospirosis vaccination for all dogs, researchers said. The bacterial infection is expected to become more common with climate change.

“This is a really important One Health problem,” Sykes said. “It affects dogs and it affects people.”

More information

The U.S. Centers for Disease Control and Prevention has more about leptospirosis.

SOURCE: University of California-Davis, news release, May 26, 2026